Graduate Electrical mystery

1016 Views 5 Replies 4 Participants Last post by 930cabman, Nov 16, 2020

ChiefBre9

Discussion Starter · Nov 15, 2020

I recently bought an '86 Graduate, with low miles, and begin to repair/replace all the bulbs. At that time, the lights
connected by # 9 fuse worked fine. This circuit has the RF parking light, engine bay light, RF side marker, & LR tail light.
However it blew the 7 amp fuse, and I thought it was a direct short. I have been unable to identify the short. The RF turn signal & rear work fine, and I took the entire RF assembly out, bench treated it, put it back & checked on the car & all there works fine. Multimeter shows 7 amps current, blowing the 7 amp fuse. So, do I install the 16 amp fuse now, or keep checking each area where there could be a short? I found that several of the blade connectors had corrosion, so cleaned them with contact cleaner & a nail file. Help! ChiefBre.

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pescara

· #2 · Nov 15, 2020

You have a + that is connected with earth somewhere.

Check all the terminals again, check the lamps. You may have a slightly bare wire (age, friction) that is in contact with the body. Wires under the hood (for engien bay) for example.

Usually, 10 A fuses are there.

Good luck

Chris

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ChiefBre9

Discussion Starter · #3 · Nov 16, 2020

pescara said:
You have a + that is connected with earth somewhere.

Check all the terminals again, check the lamps. You may have a slightly bare wire (age, friction) that is in contact with the body. Wires under the hood (for engien bay) for example.

Usually, 10 A fuses are there.

Good luck

Chris

Exactly what I thought; but it is still a mystery as to why it worked correctly for a few months & then...I suspect that the yellow/black wire(hot lead for that circuit) is either chafing somewhere, OR somewhere behind the fuse box it is loose
& touching ground. I checked the ampere draw on the LF parking light; it was about .6 of an amp. I am sure there is no ground between the spade connector behind the RF headlight, since I separated these & no short. So, it has to be in the engine bay light(unlikely since it is all exposed),. or the side marker at RF(but I have removed the bulb & checked the wire along its length) so now down to LR side marker or LR tail light.

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pescara

· #4 · Nov 16, 2020

With the voltmeter , on the "sound function for continuity", check if there is electrical continuity between the "+" wire and the ground. For each "+" wire. The voltmeter shouldn't make noise. If so, then you have the damaged wire.

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Jim G

· #5 · Nov 16, 2020

When replacing the bulbs in the taillight bulb holders. Its easy to push the copper strip that goes along the side of the bulb down into the strip that touches the center of the bulb. Which cause a short.

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930cabman

· #6 · Nov 16, 2020

Welcome to the world of our beloved "electric gremlins", all the while your Alfa is 35 years young. Given the number of electrical connections with our spiders it's a miracle they work at all. Take your time and go through them one by one, following the wiring/connections. It sounds as though you are on the right track, just keep moving forward.

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