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rlutterb
Samba Member
Joined: January 10, 2006
Posts: 1417
Location: Carrollton Ohio
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 Posted: Sun Jan 11, 2015 12:12 pm Post subject: 72 bus dash light problem |
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I have a 1972 bus with dash light problems. When I turn on the headlights the gas gauge pegs to full. when I put the headlights on and use the instrument panel dimmer switch and turn it all the way down the gas gauge works but when I brighten the instrument panel lights all of the way the dash lights get brighter but the gas gauge Pega two full. I have checked all wiring from the light switch and it all is in the right spot with the correct grounds. Bany thoughts on what is causing this? I am thinking a bad headlight switch.
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kreemoweet
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Joined: March 13, 2008
Posts: 4115
Location: Seattle, WA
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| Posted: Sun Jan 11, 2015 12:41 pm Post subject: |
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| rlutterb wrote: |
| ... it all is in the right spot ... |
Well, it obviously isn't, eh? 'Cuz if it was, then it would be working OK.
The gas gauge is not connected to the light switch in any way, and
a bad light switch would not affect the gauge reading (assuming correct wiring). Look closely at your wiring diagram and check again.
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busdaddy
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Joined: February 12, 2004
Posts: 53052
Location: Surrey B.C. Canada, but thinking of Ukraine
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| Posted: Sun Jan 11, 2015 1:11 pm Post subject: |
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Is the ground wire connected between the spade on the cluster shell and the tab on the body near the wiper motor?, are both ends clean and tight?
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Vince Waldon
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Joined: November 07, 2010
Posts: 451
Location: Edmonton, Alberta
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| Posted: Sun Jan 11, 2015 1:17 pm Post subject: |
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Yup.. most likely something you think is grounded... isnt. 
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SGKent 
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Joined: October 30, 2007
Posts: 42820
Location: at the beach
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| Posted: Sun Jan 11, 2015 3:14 pm Post subject: |
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| busdaddy wrote: |
| Is the ground wire connected between the spade on the cluster shell and the tab on the body near the wiper motor?, are both ends clean and tight? |
thst was my initial thought but then I couldn't make that work in my mind.
The wiring diagram for a 1972 shows S-11 fuse power coming in to the alternator warning lamp, turn signal warning lamp, oil pressure warning lamp, and the gauge.
On the return side each warning light goes to its own ground (oil pressure switch, light high low relay, VR etc), and the gauge goes to ground through the gas sender only. There is no connection that I can see between these lights/gauge and the dash cluster backplane.
Walk me thru the voltage flow as I can't make it work nor can I figure out his problem.
http://www.thesamba.com/vw/archives/info/wiring/bus_8_71_1700.jpg
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busdaddy
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Joined: February 12, 2004
Posts: 53052
Location: Surrey B.C. Canada, but thinking of Ukraine
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| Posted: Sun Jan 11, 2015 4:27 pm Post subject: |
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What I'm thinking is the collective resistance of the dash light bulbs is powering the back of the cluster when it has no ground path, the fuel gauge also uses that same ground to regulate it's voltage internally (the vibrator is built in on early models), turning up the dash lights changes the fuel gauges base voltage and odd readings occur. Of course he could just have a wire on a wrong terminal as well, wouldn't be the first time.
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Lil Lulu
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Joined: December 08, 2007
Posts: 1790
Location: Mouth of the Columbia
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| Posted: Sun Jan 11, 2015 5:54 pm Post subject: |
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I had similar problems with my '72. I found that although the grounds looked good, they were in fact not grounding. Cleaned and shined all the connections and problem solved. They were just corroded and crusty.
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rlutterb
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Joined: January 10, 2006
Posts: 1417
Location: Carrollton Ohio
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| Posted: Sun Jan 18, 2015 9:39 am Post subject: |
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| busdaddy wrote: |
| Is the ground wire connected between the spade on the cluster shell and the tab on the body near the wiper motor?, are both ends clean and tight? |
That ground wire was missing. Seems to have fixed it. Only thing I see now is that my gas gauge no longer reads full it reads like it's almost empty so I'm off to the gas station to see if that is accurate or not
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rlutterb
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Joined: January 10, 2006
Posts: 1417
Location: Carrollton Ohio
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| Posted: Thu Feb 12, 2015 1:32 pm Post subject: |
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Ultimatly it indeed was the missing ground wire connected between the spade on the cluster shell and the tab on the body near the wiper motor.
It all works fine now. Gas guage jumps occationsally but I think that is the sender in the tank.
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1973 Super Beetle project
1978 VW convertable
1987 El Camino
1995 Miata M
2015 Chevy Silverado |
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