Crazy electrical problem

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May 1, 2009
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I've been fighting electrical gremlins for a couple of weeks now (no headlights in spite of 12v at plug, similar problem with turn signals). By chance I discovered tonight that when I disconnect the negative battery terminal, I still have + 9 volts from the positive battery terminal to the chassis (and about 3 from the negative battery terminal to the chassis). What can cause this?

I suspect a short, just not a large enough one to burn out the mythical fusible link.

When checking the hot side of the fuse box,with all the fuses out, none have continuity to ground. When checking the cold side of the fuse box, the ignition fuse (B/Y wire) is shorted to ground. I disconnected it from the coil and still it is shorted to ground.

So my conclusion is that the B/Y wire is shorted to ground somewhere.

Before I pull the harness out, does this make sense to everyone?
 
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The B/Y wire goes to other places besides the coil like the throttle solenoid which would be very low ohms. Search and find the schematic. If you think there is a wire shorted to ground then run a new one, out the door if nessesary to test your theory. Find the problem before you tear into it.
 
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Even with that fuse out, the chassis is still positively charged so there must be another problem correct?

I've been staring at the diagram for days.
 
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What can cause this?

Trying to measure voltages on an open circuit can cause this.

The voltages you measured don't mean anything. Make sure all the wires and plugs are connected and the appropriate switch is turned on. Then if you measure a voltage it will mean something.

Most of the fused circuits have switches, so you won't see a ground until you turn the switch on.

There is no fuse on the ignition wire. The engine fuse has several B/Y wires that run other things, like the idle fuel solenoid.
 
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Adax,

I had a similar problem with my headlights and it ended up being the switch. I opened it up, cleaned it all out and re-assembled. After doing all that I found that it was the plug itself that was not making a good connection. Bent a couple thingies in the plug and all was good.

The fact that your turn signals are also not working is troublesome though. It would make sense that if you have a problem with one, then it's probably the same problem with both, which goes back to a ground, right?

Good luck!
 
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To quote Carroll, curiouser and curiouser.

Thanks for the input. Let me get back to the original problem to see if that helps.

I measure 12v at the headlight plugs (both) and the Hi/Lo switch works correctly.

When I plug in a light, nothing happens - I've cleaned the connections and have dielectric grease on them.

I removed and cleaned the switch thoroughly and it works correctly according to my meter. The switch plug has +12 at the red wire as it should. Now, If I connect that red wire (it is hot supply to the switch) to the light with a jumper, nothing happens (yes, the other terminal is grounded appropriately). So the problem is before the switch and it seems to be that when the circuit sees a load, voltage drops to zero (or there is very little current to begin with). I can light the headlight when jumpered off the fuse.

The turn signal problem is the same: measuring +12 everywhere, all switches working, but no light when a load is applied. (If I jumper 12v from the hot wire at the flasher, it will not light the headlight.)

I'm running out of diagnostic tests.

AC
 

Blue77FJ40

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Are you sure that the headlamps are not blown?

Have you jumpered a ground for the turn signals to see if they are/are not properly grounded?
 
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Yes, ground the ground. Pull a ground jumper to you device from the battery terminal, and then test for a circuit...I'm leaning toward a bad ground to your chassis
 
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I measure 12v at the headlight plugs (both) and the Hi/Lo switch works correctly.

When I plug in a light, nothing happens -
The turn signal problem is the same: measuring +12 everywhere, all switches working, but no light when a load is applied.
AC

This is telling you that you have a bad (high resistance) connection somewhere up stream of the lamps to the fuse block. When you plug in the lamp, you have a complete circuit. If you have zero voltage at the lamp when it is plugged in, it is because the bad connection isn't letting enough current flow. When you unplug it, you have voltage because because there is no flow other than tthat which the meter is seeing.

Plug the lamps in and keep following the circuit back to the fuse block and measure the voltage. you will find a point where the voltage jumps up to 12V and the bad connection is just after this point.
 
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Plug the lamps in and keep following the circuit back to the fuse block and measure the voltage. you will find a point where the voltage jumps up to 12V and the bad connection is just after this point.

Makes sense, thanks. I'll work on it tonight but I think based what I've done so far it is between the fuse box and the headlight switch connector plug. At least for the headlights.

AC
 

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