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Amskeptic Samba Member
Joined: October 18, 2002 Posts: 8568 Location: All Across The Country
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Posted: Mon Dec 22, 2008 10:23 pm Post subject: Double Relay Explained. . . In Color! |
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[url=https://www.thesamba.com/vw/forum/viewtopic.php?t=334340&start=0&postdays=0&postorder=asc&highlight=]Double Relay Explained. . . In Color![/url] |
Relays allow you to switch heavy duty or far away devices with light duty switches.
In the case of the rear-engined VW, we get to instruct the starter to turn over the engine with a very light wire telling the starter relay to hook up the heavy duty battery cable with the equally heavy duty starter motor wire.
The convention with generic German car relay numbering is that the power supply wire is designated #30, the destination wire is #87, the instruction wire is #86, and the ground wire is #85.
Relays
http://i187.photobucket.com/albums/x133/73VW1800/Tech/IACRelay.jpg
In German car wiring diagrams, #30 is used not only on relays, but any time a wire is "hot". If your battery is hooked up and charged, expect full voltage at any #30 terminal you happen across. #15 is found wherever you get battery voltage when the ignition key is turned to the "on" position, that would include the #15 terminal on your ignition coil. #50 is used for any wire that receives voltage when the key is at "start."
So here is our generic, simplified double relay diagram with conventional numbering just for us. All the double relay does is two things:
1) Supply voltage to the fuel injection system when the ignition is on.
2) Supply voltage to the fuel pump under two specific instructions,
a) when starting,
b) when the engine has informed the relay that it is now running under its own power.
Simplified
http://i187.photobucket.com/albums/x133/73VW1800/Tech/DoubleRelay1.jpg
Alas, it cannot be so simple. You will also see only little adherence to the German electrical system numbering conventions at the double relay itself. But if you compare the colors used in the above generic diagram to the colors below in the actual current path diagram of your Volkswagen L-Jetronic fuel injection system, you will see the simple functions of the double relay. The ignition circuit is colored in green and it instructs the *power* relay to provide voltage to the injectors, via the voltage dropping "series resistors", and the Electronic Control Unit. The starting circuit is colored in pink. It runs the *fuel pump* relay which supplies voltage to the fuel pump, and the Auxiliary Air Regulator.
Off
http://i187.photobucket.com/albums/x133/73VW1800/Tech/DoubleRelayOff.jpg
Let's run you through the sequence: First, we turn on the ignition. Power relay gets energized and the ECU and series resistors have voltage. The engine is not turning though, so we certainly don't need a fuel pump just yet.
Ignition On - Engine Off:
http://i187.photobucket.com/albums/x133/73VW1800/Tech/DoubleRelayOn.jpg
But, as soon as we turn the ignition key to "start" we need fuel pump and we need some cold starting assistance. (the ignition side is energized as above, but I have darkened the display to keep you focused on the starting side) With the ignition key at #50, voltage is supplied to the starter which is now turning over the engine. Voltage also continues to the double relay where the fuel pump relay is energized and connects supply voltage to the fuel pump and the Auxiliary Air Regulator (it only needs voltage to energize a timed heater). You will note (!) that there is another circuit that is energized OUTSIDE of the double relay function, the 86a > 86 terminals are "bussed" and voltage goes down to the cold start valve quite independently of anything going on inside the double relay. The cold start valve is limited to operating only when the starter #50 circuit is energized, and it shuts off when the Thermo Time Switch cuts the ground path. Like the Auxiliary Air Regulator, the Thermo Time Switch only needs voltage to energize an even faster timed heater than the AAR's.
Starting:
http://i187.photobucket.com/albums/x133/73VW1800/Tech/DoubleRelayStart.jpg
When the engine starts, we release the ignition key. The starter circuit drops out. The CSV and TTS are cut off as well. And inside the double relay, the fuel pump relay is going to want to drop out as well. . . . but, it doesn't. Thanks to the Air Flow Meter, which has determined that the engine is running all by itself, the power relay voltage that has been supplied to terminal #88a to the AFM all of this time, now gets to return to the fuel pump relay through 86b, illustrated with a shocking blue/red striped wire. There is a diode inside the relay that prevents the AFM voltage from running out to try to engage the starter and cold start valve, so all that happens is that the fuel pump and AAR are allowed to continue to run only so long as the AFM is reading air flow. If you stall the engine, well, consult "Ignition On - Engine Off" diagram.
Engine Running:
http://i187.photobucket.com/albums/x133/73VW1800/Tech/DoubleRelayRun.jpg
Actual wire colors and locations are unfortunately not nearly so beautiful as depicted. This might be a good thing. All wiring in the L-Jet fuel injection system is white. Vehicle wiring is color-coded.
Actual Wire Colors:
http://i187.photobucket.com/albums/x133/73VW1800/Tech/DoubleRelayWireColors.jpg
Now this is disappointing. After that nice elegant distribution of terminals in a logical way in all of the above diagrams, I have to show you the actual layout. It looks willy-nilly, but it is what VW/Bosch had to do to separate the vehicle harness from the fuel injection harness, and still get all the tracks and bus bars laid out inside the double relay. The view of the relay underside is as if you laid it on its firewall "back" side. The plugs are oriented as if you just pulled them off and stared down at them. The left plug is the vehicle harness, you can see multi-colored wires. The right plug is all white wires leading into their harness. People get confused trying to read the terminal designations on the relay and then transposing the correct terminal number onto the correct plug "slot", so here I have labelled both the double relay terminals and the plug terminals.
Plugs
http://i187.photobucket.com/albums/x133/73VW1800/Tech/DoubleRelayPlugs.jpg
Note that with the correct wiring colors on the preceding diagram, you can catch that blue/red wire on the left and know instantly that it is the fuel pump supply wire coming from relay terminal #88d. From here on out, you will know that if your car refuses to start readily when cold, you can double check the red/white wire from the starter solenoid #50 terminal to make sure it is sending voltage to the double relay #86a where it buses right back out from #86 to fire up the CSV Cold Start Valve.
Enjoy. This is not terribly complicated stuff, just annoying when wires and terminals get all bunched up and you can't read designations. More to come. . .
Colin
(if your specific bus has slightly different terminal designations, do not panic. For example, the late '78-'79 buses grounded the relays internally instead of the outside wire trapped under the bracket screw. '76 buses had an electrically-controlled EGR that borrowed off the double relay. The entire series resistor pack was deleted when they discovered that they get the same voltage drop within the wires to the injectors, roll with it) _________________ www.itinerant-air-cooled.com |
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regis101 Samba Member
Joined: July 28, 2005 Posts: 2078 Location: Livermore, Ca
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Posted: Mon Dec 22, 2008 10:56 pm Post subject: |
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Very Nice.
I'm looking at the schematic(s) in the Bentley. Our 78 Cali uses the 11 pin relay. I see 12 pins on the drawings. The difference being 85 and 85a which are grounds. No big.
The 79 Cali uses a 13 pin. Pretty much the same except for power taken to the injectors for cylinders 1 & 2 and 3 & 4.
(roll with it) quote, unquote
Thanks, _________________ Peace, Regis |
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evanwilliams4u Samba Member
Joined: December 16, 2008 Posts: 88 Location: California
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Posted: Mon Dec 22, 2008 11:12 pm Post subject: |
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Nice drawings. It's a real talent to be able to bring life into wiring schematics, and helpful too! _________________ 1978 Stock Westfalia Deluxe |
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Wildthings Samba Member
Joined: March 13, 2005 Posts: 50338
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Posted: Tue Dec 23, 2008 12:46 am Post subject: |
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In the second drawing labeled L-jet Double Relay Simplified the cold start valve is wired wrong. It is not fed power off the relay at terminal 88d , but gets its power from the trigger circuit (#50) for the relay at terminal 86, as shown in the more detailed drawings. |
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greenbus pilot Samba Member
Joined: March 14, 2008 Posts: 1285 Location: Wisconsin: Rustbelt, USA baby!!
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Posted: Tue Dec 23, 2008 12:48 am Post subject: |
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Wow Colin, very nice! At last, an easy to read explanation all laid out in color.
So, when is your book gonna be out? _________________ Sent from a white van down the street. |
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asafk Samba Member
Joined: April 15, 2008 Posts: 81 Location: Israel
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Posted: Tue Dec 23, 2008 1:28 am Post subject: |
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Looking at the wiring diagram of the '78 L-jet, I see a resistor in line with 86b. I don't see it in the very helpful drawing you've made. what do I miss? (I usually miss something... )
Asaf. |
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Amskeptic Samba Member
Joined: October 18, 2002 Posts: 8568 Location: All Across The Country
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Posted: Tue Dec 23, 2008 1:31 am Post subject: |
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Wildthings wrote: |
In the second drawing labeled L-jet Double Relay Simplified the cold start valve is wired wrong. It is not fed power off the relay at terminal 88d , but gets its power from the trigger circuit (#50) for the relay at terminal 86, as shown in the more detailed drawings. |
Ya rope em slowly, Wildthings. That picture was just to get the conceptual flow established, that is why I used INCORRECT terminal numbering as well. . .
Colin _________________ www.itinerant-air-cooled.com |
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Amskeptic Samba Member
Joined: October 18, 2002 Posts: 8568 Location: All Across The Country
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Posted: Tue Dec 23, 2008 1:41 am Post subject: |
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asafk wrote: |
Looking at the wiring diagram of the '78 L-jet, I see a resistor in line with 86b. I don't see it in the very helpful drawing you've made. what do I miss? (I usually miss something... )
Asaf. |
As I mentioned to Wildthings, I am most interested in people getting the concept down, and seeing how the factory answered the question, "how do we get the fuel pump to run during start and run only after the engine has proved that it is running?"
I didn't think that was the place to chase down the arcana of resistance to not only limit the current through the AFM 36/39 contacts to help them last longer but also setting the threshold for the diode as per this thrilling aside:
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Diodes are components that allow current to flow in only one direction. They have a positive side (leg) and a negative side. When the voltage on the positive leg is higher than on the negative leg then current flows through the diode (the resistance is very low). When the voltage is lower on the positive leg than on the negative leg then the current does not flow (the resistance is very high). The negative leg of a diode is the one with the line closest to it. It is called the cathode. The postive end is called the anode.
Usually when current is flowing through a diode, the voltage on the positive leg is 0.65 volts higher than on the negative (the resisted) leg. |
_________________ www.itinerant-air-cooled.com |
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Amskeptic Samba Member
Joined: October 18, 2002 Posts: 8568 Location: All Across The Country
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Posted: Tue Dec 23, 2008 1:46 am Post subject: |
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greenbus pilot wrote: |
Wow Colin, very nice! At last, an easy to read explanation all laid out in color.
So, when is your book gonna be out? |
Man, I am in the thick of it. I wonder if it will have a market if we continue to suffer this economy. Jobless and bored? Read this book about that classic car you don't want to sell with EZ On The Eye Illustrations. I dunno. Still working on it. Want it done!
Colin _________________ www.itinerant-air-cooled.com |
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Wildthings Samba Member
Joined: March 13, 2005 Posts: 50338
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Posted: Tue Dec 23, 2008 2:25 am Post subject: |
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Seems like posting a conceptual drawing that is incorrect is kind of like roping a fence post. Causes that conceptual flow to come to a stop pretty quick. |
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aeromech Samba Member
Joined: January 24, 2006 Posts: 16961 Location: San Diego, California
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Posted: Tue Dec 23, 2008 8:15 am Post subject: |
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Amskeptic, thanks for the great posting. i could have used that a couple months ago. |
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dan macmillan Samba Member
Joined: October 19, 2003 Posts: 3110 Location: Northern Ontario, Canada
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Posted: Tue Dec 23, 2008 9:00 am Post subject: |
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Quote: |
Wildthings
In the second drawing labeled L-jet Double Relay Simplified the cold start valve is wired wrong. It is not fed power off the relay at terminal 88d , but gets its power from the trigger circuit (#50) for the relay at terminal 86, as shown in the more detailed drawings.
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Wildthings wrote: |
Seems like posting a conceptual drawing that is incorrect is kind of like roping a fence post. Causes that conceptual flow to come to a stop pretty quick. |
Give the guy a break. He has taken what many consider to be a mystery and broken it down so anyone can understand it.
It is an over simplified version of the actual circuits used to illustrate the CONCEPT of how it works. Yes it is wired wrong BUT it will accomplish the same thing as the correctly wired diagram other than the fact that the CSV will recieve power at all times with the key on. The TTS will shut down the CSV as it warms up. [Moving the CSV circuit to term 50 of the starter and adding a diode in between term 50 and term 84 {of the double relay simplified drawing} would make it electrically correct. However. that is not necessary as the next diagram clears it up and his description makes it easy for people to follow.] The terminal designations are that of a standard relay. Keep in mind that the concept drawing uses easily obtainable, low cost, standard bosch relays. Using his description and diagrams one could easily build their own double relay for under $20.00
Amskeptic, you have done an excellent Job of describing the operation of the double relay. I am sure it will help many people understand it. _________________ Licensed Automotive Service Technician
Licensed Truck and Coach Technician
Licensed Heavy Duty Equipment Technician
CFC/HCFC/HFC A/C handling and installation license
Alignment specialist
66 Modified Manx,68 Kyote,74 Thing,74 Beetle, 76 Transporter,75 self made Double Cab,65 Meyers Manx,78Westy,68 Ghia, 79 Bradley GT2
Current projects:
Built for others:69 Manx Clone |
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theizzardking Samba Member
Joined: June 13, 2008 Posts: 2097 Location: seattle
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Posted: Tue Dec 23, 2008 9:26 am Post subject: |
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very nice! but i'm just thinking to my self actual wire colors is kind of a relitive term as i wonder how many of my wires are og! hahaha! still very well written and clear graphics good job! _________________ "Democracy is two wolves and a lamb voting on what to have for lunch.
Liberty is a well-armed lamb contesting the vote." - Benjamin Franklin
'71 westie "the wanderer" |
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busdaddy Samba Member
Joined: February 12, 2004 Posts: 51130 Location: Surrey B.C. Canada, but thinking of Ukraine
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Posted: Tue Dec 23, 2008 9:53 am Post subject: |
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Great post Colin, trying to explain electrics to some people is like describing color to a blind man and this really helps. _________________ Rust NEVER sleeps and stock never goes out of style.
Please don't PM technical questions, ask your problem in public so everyone can play along. If you think it's too stupid post it here
Stop dead photo links! Post your photos to The Samba Gallery!
Слава Україні! |
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WhirledTraveller Samba Member
Joined: January 09, 2008 Posts: 1399 Location: Cambridge, MA
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Posted: Tue Dec 23, 2008 9:54 am Post subject: |
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Thank you Colin!
Reading this post has suddenly resulted in an ah-ha moment for me. You know one of those moments where your brain suddenly connects totally separate facts into a revelation. I think I may have found the source of several of my troubles.
My '77 Bus fuel pump runs continuously with the ignition on. I've always known this and never really thought much about it.
Seperately, I've been having other issues... idle is poor until warmed up, and there's a hesitation when accelerating if I try to drive away right away, but then after a long highway drive it will sometimes die randomly at stops. Recently I took a long road trip and my MPG dropped each leg - 1st tank 17.5 mpg, 2nd tank 15.5 mpg, 3rd tank 14.5 mpg. Outside Temperature was dropping each leg also, and pulling into home with 11 degrees F outside the bus would occasionally die randomly at idle, then start right back up again. Exhaust smells rich at idle. I've replaced the Temp Sensor II, no change.
So now - looking at your diagrams - It occurs to me that if the fuel pump is always running due to incorrect starter wiring then the cold start valve may also be energized through the thermo-time switch. The TTS should shut the cold start valve off after 8 seconds BUT it's not intended for continuous use. It might let some current through, particularly if the temperature in the engine compartment is very low I'd imagine it would cycle on and off as the TTS turns on, heats, shuts off, cools, turns on etc, randomly killing my engine with extra fuel. _________________ 1977 Westy, Automatic. Big Valve heads, CS Cam. |
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Lionhart94010 Samba Member
Joined: January 04, 2005 Posts: 1417 Location: SF Bay Area / Silicon Valley / So Cal
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Posted: Tue Dec 23, 2008 10:54 am Post subject: |
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Very nice explanation :0) thanks for the effort /contribution!
Noting to add, but want to follow this thread… _________________ Current VWs 71 T2 Westy SO-72/6(Miami), 71 Crew Cab, 2015 GSW TDI
Other owned VW’s 59, 68 1500s, 69 & 71 Bug’s; 72 & 73 S-Bug’s; 67 Westy, 67 Deluxe, Other 71 DC, 72 KG GT that now lives in Australia, 12 JSW TDI, 2015 GSW TDI, 2023 Tiguan
VW technical information sights
thesamba - www.ratwell.com - www.shoptalkforums.com/ - www.vw-resource.com - http://www.type2.com/
http://bobhooversblog.blogspot.com/ - www.aircooled.net/gnrlsite/resource/articles.htm |
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busman78 Samba Member
Joined: August 17, 2004 Posts: 4522 Location: Oklahoma City, OK
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Posted: Tue Dec 23, 2008 1:25 pm Post subject: |
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I am not a FI type of guy but I do applaud Colin's drawings, not everybody out in the VW world is a 100% know-it-all and thank god not as arrogant as dan. |
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onion456 Samba Member
Joined: September 09, 2006 Posts: 674 Location: Houston, TX
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Posted: Tue Dec 23, 2008 1:42 pm Post subject: |
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allow me to be off topic by being more on topic- colin i think your drawings are outstanding- these and also i saw one about double-clutching- exceptional work. as an electronics kinda guy, i often do explanitory drawings or write-ups, and i understand the work that goes into it. yours are top notch. _________________ '76 Sage Green Westy 2.0 FI
'76 Creamsicle 7-passenger 2.0 CS FI
'85 Tan Westy |
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germansupplyscott Samba Member
Joined: May 22, 2004 Posts: 7093 Location: toronto
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Posted: Tue Dec 23, 2008 2:22 pm Post subject: |
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please people, don't let the thread get out of control.
wildthings, dan, this has nothing to do with your vehicles or your expertise.
it's about some cool drawings that colin posted. i think they're cool, yes. if the drawing of the relay has the wrong number of terminals or a wire in the wrong spot i'm sure colin will fix it. _________________ SL |
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onion456 Samba Member
Joined: September 09, 2006 Posts: 674 Location: Houston, TX
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Posted: Tue Dec 23, 2008 2:41 pm Post subject: |
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i see the 'simpified' drawing to show how a generic relay, when energized, will supply power to the various devices. his drawing shows that terminal 87 of the generic relay to be the heavy duty terminal. (as referenced by the preceeding drawing, explaining a generic relay)
it was probably unnecessary to number the terminals at all, since it is just a simplified drawing, like a block diagram. the more detailed drawings below show the correct terminal numbers, as those are not a generic relay, but the VW dual relay we know and love/hate.
makes sense to me
on the other hand lol, regarding the CSV and TTS, i was under the assumption that the TTS controls ground for the CSV; that the TTS is a temperature controlled switch that interrupts the ground circuit for the CSV. if the TTS is open, theres no ground connection and the CSV cant fire. this is not really shown in the drawing, it looks like they are sharing a ground connection. i dont know that its really necessary to fix the drawing, as the focus of the drawing was the dual relay and not the components, but if you were inclined to fix it, its just a small detail. _________________ '76 Sage Green Westy 2.0 FI
'76 Creamsicle 7-passenger 2.0 CS FI
'85 Tan Westy |
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