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Volkswagen Rabbit, Jetta, Scirocco, Convertible: 1975-1984 (A1) Bulb check relay?


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Last Post: Mar 19, 2007 3:04 PM Last Post By: tcovenant2000
82_Jetta_Diesel

Posts: 42
Registered: 09/01/05
Bulb check relay?
Posted: Feb 10, 2007 8:30 AM
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82 Jetta diesel - I'm having an intermittent but predictable problem with my temp and fuel gauges. When the cabin of the car is cold, say around 50 deg. F, the gauges work fine. When the heater warms up the cabin the gauges quit. If I turn down the heat and the cabin cools, the temp light will flash and the gauges will work again.

Some background. I don't see anything about the bulb check relay for my car in Bentley although it does describe it for the 80 rabbit? When I first turn on the key, all the warning lights flash. When the gauges quit and then come back on, only the temp light flashes.
tcovenant2000

Posts: 1,767
Registered: 12/09/03
Re: Bulb check relay?
Posted: Feb 10, 2007 9:47 AM   in response to: 82_Jetta_Diesel in response to: 82_Jetta_Diesel
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With the engine going, the only light that would flash or come on would be the water temp light. It sounds like you're losing power to the whole dash, not just the 2 gauges. You can verify this while driving, by pushing in the clutch and turning off the key, then turning the key back on (do this during a gauge "dead time"). If none of the lights come on then you know you've lost cluster power.
Remove the bezel. There's a 14 pin connector at the bottom of the cluster. Check the contacts for corrosion on pin 2 (ground) and pin 14 (power).
Also check the ground tree by removing all the wires and putting them back on. Do this like 3 times for each wire to clean up grounds.
My '84 has this problem and it's in the wiring where the wire meets the pin. Not sure what to do except solder it.
Thomas
82_Jetta_Diesel

Posts: 42
Registered: 09/01/05
Re: Bulb check relay?
Posted: Feb 10, 2007 8:33 PM   in response to: tcovenant2000 in response to: tcovenant2000
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I tried the test you suggested. When I turned the key back on the seatbelt and oil pressure lights came on. When you mentioned the cluster losing power did you mean everything? All the backlighting, the clock, flasher and high beam indicator still work.
tcovenant2000

Posts: 1,767
Registered: 12/09/03
Re: Bulb check relay?
Posted: Feb 11, 2007 10:26 AM   in response to: 82_Jetta_Diesel in response to: 82_Jetta_Diesel
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Not everything. With the engine off the oil pressure light and battery light should have come on along with the light inside the water temp gauge.
The backlighting, flasher and high beam should also not work.
This sounds more like the voltage regulator that supplies power only to the fuel and water temp gauges is going south on you.
The easiest thing to do for that is pull the cluster and replace it. It's cheap, but on some models may require soldering.
Thomas
82_Jetta_Diesel

Posts: 42
Registered: 09/01/05
Re: Bulb check relay?
Posted: Mar 17, 2007 2:21 PM   in response to: tcovenant2000 in response to: tcovenant2000
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Thomas,

Thanks. I finally replaced the transistor. Well, the problem is still there although it doesn't seem as bad as it was. Any other ideas I could try?

By the way ... the transistor cost $24. Being in electronics I tried to cross match the old one first but no luck. When I got the new one I did the same thing and it is still a valid P/N from the manufacturer. It's $0.60 plus S&H. No much of a markup there!
tcovenant2000

Posts: 1,767
Registered: 12/09/03
Re: Bulb check relay?
Posted: Mar 18, 2007 12:48 PM   in response to: 82_Jetta_Diesel in response to: 82_Jetta_Diesel
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Heh...sorry about that. I should have told you that the 7810 regulator is what you seek. 60 cents sounds about right.
The problem is still there? Then you've got a connection problem somewhere. Likely a crack in the plastic circuit board on the cluster. Might be worth your while to hit a junkyard and get another.
Thomas
82_Jetta_Diesel

Posts: 42
Registered: 09/01/05
Re: Bulb check relay?
Posted: Mar 18, 2007 1:51 PM   in response to: tcovenant2000 in response to: tcovenant2000
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Thomas,

No need to apologize as I really appreciate your help. You mean the L-shaped board, correct? I'll take a look at it and see if I see anything. Thankfully I work in electronics. I have access to some very skilled PCB repair folks. Now, if it has defective parts that react to heat then that's a trip to the junkyard.
tcovenant2000

Posts: 1,767
Registered: 12/09/03
Re: Bulb check relay?
Posted: Mar 19, 2007 3:04 PM   in response to: 82_Jetta_Diesel in response to: 82_Jetta_Diesel
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The L shaped board could be at fault, but so could the whole flexible PC board. It has traces running everywhere. A bit harder to repair, but not impossible. The main problem that's tough is when there's a problem at the edge connector that meets the harness. That is usually a trip to the 'yard.
Good luck!
Thomas

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