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Old 04-12-2019, 05:31 PM
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Default Don't know where to begin

Yesterday I started up my 72 GTO, let it warm up and checked the timing. Decided to advance it from twelve to fourteen just to see if it would run better. Checked the vacuum and it's at about 19 inches. Closed the hood and go for a test drive. Less than a mile away from my house the car died, I mean TOTALLY died. Lost ALL electricity. So far, I see nothing that's melted down or looks of failure. I didn't find any blown fuses. I did smell SOMETHING that wreaked of electrical short, though it was very faint.

Any ideas where to start? I had Triple A flatbed he car back to my house.

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Old 04-12-2019, 05:46 PM
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Did you have head light or starter still crank?
Start looking the harness over, something burnt up
Is the car an automatic?

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Old 04-12-2019, 05:57 PM
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check wire path to starter for crusty wires.

a classic for somebody ( not mee) has been the fuse block bolt being loose and the engine harness backed out.

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Old 04-12-2019, 06:09 PM
mgarblik mgarblik is offline
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Based on the title of your thread, the place to begin is at the beginning. Everything starts at the battery, so start there. First perform a complete visual inspection of the underhood electrical system. Battery cables, negative to the engine. Battery lead to the alternator and starter. Use a test light or a DVOM would be better. Should have 12.4V minimum to the ALT and starter main lead. Then check what does and does not work. If the entire electrical system is dead, no lights, no horn, wipers, blower motor, dash warning lights, it has to be one of the few main power or ground leads. If some stuff works and other stuff does not. report back so you can get some more direction. Good luck. It is almost certainly a SINGLE problem when many circuits go dead at once.

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Old 04-12-2019, 06:11 PM
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I've had a couple of fairly new batteries totally crap out all of a sudden late. As he said check from the start.

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Old 04-12-2019, 06:16 PM
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Check the bulkhead connectors at the firewall in the engine compartment that attach to the fuse block inside the car. BTDT.

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Old 04-12-2019, 07:00 PM
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Factory wiring harness?

I've seen fusible link wire blow out from old age. No short, no overload, just what they're made out of gets stiff, corroded and crusty. Just poof and they're gone for no apparent reason.

Clay

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Old 04-12-2019, 07:00 PM
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Thanks guys for your quick reponses. I just found the culprit that started it all. A splice in the 12v ignition wire to my HEI grounded against the dipstick tube. Still looking for the solution as I have NO electrical at all. The car is automatic, and, no the lights, horn, nothing electrical works. So my question now is what is the primary point of electrical distribution as I believe that's where the problem is. I have a 660 jump box that I hooked up after disconnecting the battery, and still no go.

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Old 04-12-2019, 07:09 PM
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Check the fusible link wire. Don't know exactly where they're at on the 72.

Bolted down with the starter + cable
Back of alternator
At horn relay

Should be one of those places. And they do blow out when you have a short

Clay

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Old 04-12-2019, 07:22 PM
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Ok, just checked the bulkhead connector inside and out but saw nothing unusual there. Tomorrow, I will pull the starter and see if the battery cable has been compromised. Since that's the only place that the battery is directly connected to, the problem may lie there. I haven't been able to find any fusible links.

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Old 04-12-2019, 07:32 PM
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Quote:
Originally Posted by pont3 View Post
I haven't been able to find any fusible links.
It's a type of wire. The wire can blow out and the insulation stay intact. It'll stretch like a rubber band when it's blown.

Clay

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Old 04-12-2019, 07:57 PM
mgarblik mgarblik is offline
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That 12V feed to the HEI that you found shorted is protected by a fuseable link as mentioned above. I am not sure where it is located. When you find it though, it is very important that you replace it with the same amperage fuseable link wire that it came with. Do not splice regular wire in it's place. Your only other option would be to replace that wire with a proper amperage in-line fuse which would not look stock but would provide protection. BTW, a REAL parts store like a NAPA or an independent should have fusable link wire. It's doubtful anyone under 40 at an Oreily's, AutoZone, AdvanceAuto or CarQuest will have any idea what you are asking for. You will just get the "year make model ritual followed by the blank stare". Good luck.

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Old 04-12-2019, 08:11 PM
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Most of the fusible link type wiring is in the loom that connects to the alternator. Runs by the valve cover and intake. The main wire from alternator to the starter is the only source of power to everything usually.
(except the starter gets its power from battery cable, but the neutral safety wire needs 12 volts from the alternator wire to crank)


It is usually a bunch of red wires soldered together a few inches back of the alternator. Have to take the loom covering off, tape maybe? plastic covering maybe?


Probably be noticeable if it is there.
(like burnt or melted)



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Old 04-12-2019, 08:14 PM
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P.S.
Had a battery cable come loose on starter on a power shift and it shorted out against header. Instant dead. Like around midnight out in country.



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Old 04-12-2019, 08:18 PM
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A BIG THANK YOU to all of you as you have given me tips that I would never have thought of. And I've owned this car since 1987 and thought I knew every inch of it. Since I probably should replace the entire underhood wire harness, would the new one include all these fusible links?

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Old 04-12-2019, 08:25 PM
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Quote:
Originally Posted by Skip Fix View Post
I've had a couple of fairly new batteries totally crap out all of a sudden late. As he said check from the start.
Did you check the battery itself? I've had the same experience as Skip. Battery totally went dead for no apparent reason. No voltage at all across the battery terminals.

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Old 04-12-2019, 08:36 PM
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I cant find a good location, but its between the starter and the alternator. Follow the wiring from the starter up to the alternator and it has the links spliced in, the RED wire coming out, ends up at the large wire at the back of the Alternator. The Fusible Links then go to the Bulkhead Connector.

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Old 04-13-2019, 12:27 AM
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Quote:
Originally Posted by pont3 View Post
Since I probably should replace the entire underhood wire harness, would the new one include all these fusible links?
If your harness is in decent shape...I'd just replace a blown fusible link if that's the problem. And yes the fusible links are part of a new harness.

I've had to replace several that were bolted down with the battery cable on the starter solenoid. And like John said, you've got the ones behind the alternator that go inside the car.

Different makes and models had them in different locations. But they are there to protect the whole harness in the event of a short. Several circuits don't go through the fuse box and rely soley on the fusible links to prevent total melt downs.

Clay

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Old 04-13-2019, 06:51 AM
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This is schematic for 72:
Attached Thumbnails
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Old 04-13-2019, 07:05 AM
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If you have access to a service manual, page 12-40 discusses location and replacement. I snipped the page for you and attached below. It says the link is a loop of smaller gauge wire along the driver side valve cover, where it breaks out near the alternator.

I hope the pic isn't too small to be functional. I also included the underhood wiring schematic that shows the link.
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