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Old 05-16-2012, 08:06 PM
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mach4 mach4 is offline
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Quote:
Originally Posted by desmo View Post
Unplugged headlamps, didnt fix the problem.
Speedometer still dies when headlamps are on...actually dies on either of the two switch positions when tuned clockwise.
Ok we can pretty safely rule out anything related to the source of the problem being power draw. Because it happens without any appreciable draw, it most surely has to be something related to wiring - a short or a ground.

I don't have a wiring diagram for your car, but assuming that the '85 and '86 were similar in design, the only thing that is common with the cluster where the speedo is and the lights is the high beam indicator.





You didn't specify whether it only happens when the high beams are on, so you should check that. And it's worth doing a couple of things. First pulling the high beam indicator light. This won't help if the short is in the power side of things, but it would if it was on the ground side - it's worth a try. Second pull the fuse F9 (or the equivalent one for your car that handles one of the high beams and the indicator lamp). I would also pull (one at a time) the other fuses F7, F11 and F13 to see if the problem is associated with one of these circuits. Also try high and low beams for each of the configurations to see if you can find anything that is different that will provide a clue. As a last resort you could cut the WT/BU wire but certainly pulling the fuse F9 (or whatever it is on yours) would have the same effect, so save that for absolutely last.

That's all I've got for now...

If you've got an electrical manual, I could look further.
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300 sdl unique speedometer problem-hd-lt.jpg  
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