Charging System Troubleshooting--Blown Ignition Light Fuse?

[patrickt]

1) If you have a MSD "Noise Filter" capacitor installed, that will indeed hold a small charge after you've disconnected the battery. Always flick on your lights, or hold the horn button down for a second or two, after disconnecting your battery.

2) You do not need to remove the dash. Just remove the half dozen dash screws and you can get your fingers down behind the top of the dash to remove the fuel gauge. Then fish the wire through the hole in the dash, plug it back in, and reinstall the gauge.

3) Remember, fuse #3 runs your wipers, gauges, and heater. If you can get the car to run and charge properly with the "bypass fused wire" running to the I terminal of the VR, with fuse #3 out, then you positively know the short is along one of the two feeds coming off of fuse #3. One of those feeds goes to your heater (that is the light green wire coming off fuse #3), the other is the White/Green wire coming off of fuse #3 that eventually becomes the solid green wire. The short is along one of those two avenues.

[patrickt]

Actually, run a fused 12v+ line to the Green Wire, which you will cut, at the ignition light. That way you can see the ignition light come on, and then go out, when the system starts charging properly. That's a better test.

[ACHiPo]

Originally Posted by patrickt

1) If you have a MSD "Noise Filter" capacitor installed, that will indeed hold a small charge after you've disconnected the battery. Always flick on your lights, or hold the horn button down for a second or two, after disconnecting your battery.

2) You do not need to remove the dash. Just remove the half dozen dash screws and you can get your fingers down behind the top of the dash to remove the fuel gauge. Then fish the wire through the hole in the dash, plug it back in, and reinstall the gauge.

3) Remember, fuse #3 runs your wipers, gauges, and heater. If you can get the car to run and charge properly with the "bypass fused wire" running to the I terminal of the VR, with fuse #3 out, then you positively know the short is along one of the two feeds coming off of fuse #3. One of those feeds goes to your heater (that is the light green wire coming off fuse #3), the other is the White/Green wire coming off of fuse #3 that eventually becomes the solid green wire. The short is along one of those two avenues.

Patrick,
It seems the voltage regulator was eliminated as a possible cause since replacing the electro-mechanical VR with an electronic VR did not fix the issue of fuse 3 blowing.

Given that does it still make sense to run a separate wire?

I tried dropping the dash without pulling the steering wheel and it won't drop low enough to get my hand behind it, so I'm pulling the wheel.

Will check back after I get the fuel gauge put back together.

Evan

[patrickt]

Originally Posted by ACHiPo

Given that does it still make sense to run a separate wire?

Yes, because you want to get the car running and charging normally first, and then search for the short on the line you've eliminated. If running a fresh, clean, fused 12v+ line to the ignition light makes the light come on, and then go out after the car starts charging (because the current through that ignition light excites the VR in to working), then you just move on to finding the short on the eliminated line. That will not be hard to do.

[ACHiPo]

Originally Posted by patrickt

Yes, because you want to get the car running and charging normally first, and then search for the short on the line you've eliminated. If running a fresh, clean, fused 12v+ line to the ignition light makes the light come on, and then go out after the car starts charging (because the current through that ignition light excites the VR in to working), then you just move on to finding the short on the eliminated line. That will not be hard to do.

Patrick,
Thanks. Ran out of daylight (and positivity) yesterday, so took a break. I'm talking to Bob this morning. Since I've eliminated the VR, alt, tach, and fuel gauge from previous testing, it seems to me it's got to be the heater or wiper circuit. Will post what I find out and next steps.

Evan

Originally Posted by patrickt

Wait 'til he sees my bill.

PS put it on my tab