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veedubmulisha
Samba Member
Joined: November 26, 2010
Posts: 2
Location: california
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 Posted: Fri Nov 26, 2010 8:04 pm Post subject: a jumpy needle |
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| my tach is wired right. its grounded proper, the negative to the coil and hooked to power. its set for a 4 cylinder. yet the needle is jumpy.. i added a resistor like in autometers tips. its still jumpy. any idea why? |
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Bierboy
Samba Member
Joined: June 17, 2009
Posts: 819
Location: East Moline, Ill.
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| Posted: Fri Nov 26, 2010 9:21 pm Post subject: Re: a jumpy needle |
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| veedubmulisha wrote: |
| my tach is wired right. its grounded proper, the negative to the coil and hooked to power. its set for a 4 cylinder. yet the needle is jumpy.. i added a resistor like in autometers tips. its still jumpy. any idea why? |
I added the diode (NOT the resistor) as suggested in this thread, and that took care of my nervous tach...
_________________
"Otto" -- my '68 vert
Bi-State VW Club
VVWCA
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PapaG1954
Samba Member
Joined: October 06, 2007
Posts: 73
Location: Fort Lauderdale,Fl.
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| Posted: Sat Jun 20, 2015 10:28 am Post subject: TACH INSTALL |
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| Discount Auto Parts has Bosch Tachs in two sizes with either black or white faces... |
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PapaG1954
Samba Member
Joined: October 06, 2007
Posts: 73
Location: Fort Lauderdale,Fl.
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| Posted: Sat Jun 20, 2015 10:31 am Post subject: Jumpy Needle |
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| Jumpy needle could be caused by grounding the unit too close to the dashboard where all your electricity is... |
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Disaster06
Samba Member
Joined: March 22, 2017
Posts: 543
Location: Huntington Beach, CA
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| Posted: Thu Jun 15, 2017 1:28 pm Post subject: Re: Installing a Tach |
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Sorry to revive this old thread but I have a 68 bug, how do I tap into the light circuit?
Also, I have a kill switch in the cab already, which is wired to the negative side of the coil. |
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ashman40
Samba Member
Joined: February 16, 2007
Posts: 15982
Location: North Florida, USA
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| Posted: Thu Jun 15, 2017 1:59 pm Post subject: Re: Installing a Tach |
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| Disaster06 wrote: |
Sorry to revive this old thread but I have a 68 bug, how do I tap into the light circuit?
Also, I have a kill switch in the cab already, which is wired to the negative side of the coil. |
By "light circuit" I assume you mean the speedo illumination circuit? This is controlled by the headlight switch. The circuit has a built in dimmer (potentiometer) in the headlight switch knob to control the brightness of the lamps in the circuit.
Looking at the trunk-side of the speedo you should see two bulb holders at 02:30 and 09:30. These are connected in series by a grey/red wire. This is the illumination wire from the headlight switch. Test this wire as a power source for your tach's light circuit. I say test, because you may find that it is too dim for your liking. If so, you can alternately tap one of the parking light wires coming off fuse #7 & #8. These are constant 12v while the parking lights are ON. There is no control over the intensity of the lights, they are either ON or OFF.
NOTE: the speedo illumination wires are NOT fused. Be careful when working with them. Short the grey/red wire to ground while the parking lights are ON and you will usually "toast" your headlight switch.
If your kill switch already runs directly to your ignition coil (-) terminal you can use this wire as your tach pickup. Just connect your tach to the wire that runs to the ignition coil and not the wire that runs to ground. As long as your kill switch is OFF (OPEN) the tach will make use of this circuit.
_________________
AshMan40
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'67 Beetle #1 {project car that never made it to the road  }
'75 Beetle 1200LS (RHD Japan model) {junked due to frame rot}
'67 Beetle #2 {2019 project car - Wish me luck!} |
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Disaster06
Samba Member
Joined: March 22, 2017
Posts: 543
Location: Huntington Beach, CA
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| Posted: Thu Jun 15, 2017 3:14 pm Post subject: Re: Installing a Tach |
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Awesome.
Thanks! |
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runamoc 
Samba Member
Joined: June 19, 2006
Posts: 5599
Location: 37.5N 77.1W
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| Posted: Thu Jun 15, 2017 5:56 pm Post subject: Re: Installing a Tach |
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Be sure and put a diode on the 'input pulse' wire to the tach! White stripe on diode towards the tach. 1N4000 up It will 'smooth' the needle.
_________________
Daily driver: '69 Baja owned 44 yrs - Plan B: '81 Rabbit Diesel LS Deluxe - Plan C: '72 Ghia
Yard Art: 2 Sandrails
Outback: '69 Ghia - '68,'69,'70,'72 Beetle - '84 Scirocco, GTI - Pair of '02 Golfs-
VW Wiring = It's just wires |
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Disaster06
Samba Member
Joined: March 22, 2017
Posts: 543
Location: Huntington Beach, CA
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| Posted: Thu Jun 15, 2017 6:10 pm Post subject: Re: Installing a Tach |
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| runamoc wrote: |
| Be sure and put a diode on the 'input pulse' wire to the tach! White stripe on diode towards the tach. 1N4000 up It will 'smooth' the needle. |
Where can I find one of those? Autozone? Or electronic specialty shop?
Are they expensive? |
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Disaster06
Samba Member
Joined: March 22, 2017
Posts: 543
Location: Huntington Beach, CA
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| Posted: Thu Jun 15, 2017 6:12 pm Post subject: Re: Installing a Tach |
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Never mind, just found them online for like .75 cents. Do they wire inline with the wire with a butt connector or something?
Sorry I have limited wiring experience. Essentially car stereos, haven't really done resistors or diodes though |
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runamoc
Samba Member
Joined: June 19, 2006
Posts: 5599
Location: 37.5N 77.1W
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| Posted: Fri Jun 16, 2017 5:09 am Post subject: Re: Installing a Tach |
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| Quote: |
| Do they wire inline with the wire with a butt connector or something? |
Yes, inline (series). I installed a diode that was 'laying around'. I was impressed at how steady the reading was after the install. Learned about here on Samba. 
_________________
Daily driver: '69 Baja owned 44 yrs - Plan B: '81 Rabbit Diesel LS Deluxe - Plan C: '72 Ghia
Yard Art: 2 Sandrails
Outback: '69 Ghia - '68,'69,'70,'72 Beetle - '84 Scirocco, GTI - Pair of '02 Golfs-
VW Wiring = It's just wires |
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garyt
Samba Member
Joined: June 14, 2015
Posts: 763
Location: Burgundy
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| Posted: Sat Jun 17, 2017 10:54 am Post subject: Re: Installing a Tach |
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| I have mine in the engine bay, seems to me useful there when timing and doesn't spoil the dash. Has worked fine for about six months and was cheapo. |
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Disaster06
Samba Member
Joined: March 22, 2017
Posts: 543
Location: Huntington Beach, CA
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| Posted: Sat Jun 17, 2017 11:02 am Post subject: Re: Installing a Tach |
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| garyt wrote: |
| I have mine in the engine bay, seems to me useful there when timing and doesn't spoil the dash. Has worked fine for about six months and was cheapo. |
i have a digital multimeter that shows dwell and rpm for when i am working on the engine bay, I just wanted something so I could get a feel for where the engine should be shifted. my speedo doesnt really show true as i have smaller tires up front so those little notches in the speedo dont really work for me. I can shift by ear but would like to have a tach anyways.
Just installed today, ended up putting it under the dash to the right of the ash tray. looks great and didnt even have to use a diode, it has minimal fluctuation. |
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runamoc
Samba Member
Joined: June 19, 2006
Posts: 5599
Location: 37.5N 77.1W
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| Posted: Sun Jun 18, 2017 6:15 am Post subject: Re: Installing a Tach |
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| Quote: |
| minimal fluctuation |
Put a diode in and you won't even have that. 
_________________
Daily driver: '69 Baja owned 44 yrs - Plan B: '81 Rabbit Diesel LS Deluxe - Plan C: '72 Ghia
Yard Art: 2 Sandrails
Outback: '69 Ghia - '68,'69,'70,'72 Beetle - '84 Scirocco, GTI - Pair of '02 Golfs-
VW Wiring = It's just wires |
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Disaster06
Samba Member
Joined: March 22, 2017
Posts: 543
Location: Huntington Beach, CA
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| Posted: Sun Jun 18, 2017 7:47 am Post subject: Re: Installing a Tach |
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| Haha. I think the fluctuation is from the engine itself. You can hear it |
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Randy in Maine
Samba Member
Joined: August 03, 2003
Posts: 34890
Location: The Beach
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| Posted: Sun Jun 18, 2017 10:01 am Post subject: Re: Installing a Tach |
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| The VDO tachs are really sensitve to "stray voltage" and that is the purpose for the diode. |
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Disaster06
Samba Member
Joined: March 22, 2017
Posts: 543
Location: Huntington Beach, CA
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| Posted: Sun Jun 18, 2017 10:42 am Post subject: Re: Installing a Tach |
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| Ah. I just got a Bosch off amazon. Does the job! |
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