Quote:
Originally Posted by ShinyC10
1986 c10 p/u
I have attatched a few pictures below. The wiring diagram is my setup no down to the T with exception of the BATT connection. I have a single 4g wire going from BATT to a 40amp maxi fuse and to the jblock. Recently, that 40amp maxi fuse blew and keeps blowing fuses every time I turn the truck on. The initial problem was the BATT stud was somewhat loose on the inside of the case so I opened it up and replace it with another stud from and old alt. The seemed to fix the problem till I drove it then it blew the fuse again. Got back home, popped the hood and put another fuse in and ran a few tests (remaining pictures in the post) and all of them show way higher numbers than what I wanted. Next step, I did a short test with a test light. Took all the fuses out and nothing seemed to be shorted out till I pulled the power accessory circuit breaker (little metal like fuse on the top right of the fuse box). That seemed to turn the test light off. I'm at a loss and need some insight.
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Well no replies yet so let me see if we can unravel this mystery. I quoted your post so I can bold the things I have questions about.
1. How are you getting power to the cab I assume off the J block since you only have 1, 4 gauge wire from the alternator. Same with the 8 gauge wire off the starter solenoid which also serves as the battery charging wire.
2. Does this mean that you blow the fuse just by turning the key on or does the truck have to be running. This is important to know, because if it's blowing just by turning the key on, it means that the circuit is shorted .
It also figures that the circuit is not shorted, because it is hot without the key on, so it would blow the fuse anytime the battery was connected.
3. If it's blowing while the truck is running, Which I suspect, it means that the maxi-fuse cannot handle the amp surge draw when the electrical loads kick in, and you may need to replace it with a rated fusible link like the one shown in the diagram.
You really don't know if the BATT stud on the alternator was shorted to the case (ground), before you fixed it. Do a continuity check on it and wiggle it around while you are checking it because the engine motion and vibration could cause it to short to ground while it was running.
While we're here you should check all the power wires to be sure they can't touch grounds while the engine is running and if the insulation is good on them. Example: any wire or cable that could be touching the exhaust.
Your two tests with the voltmeter are not much help because they only show voltage drops on the two wires you tested, and .2 volts is not much. Also were they taken with the engine running or Key off or key on.
The best thing you could do is put an amp meter on the alternator output line, and see how many amps are going to the maxi-fuse with the engine running at about 2K, while you turn on the accessories.
4. I'm guessing that the power accessory CB is not a factor because it probably doesn't come into play until your relays are closed by being switched on. How did you check it? engine on or off. Key on or off.
5. Another thing, did the engine die when the fuse blew or did you just see that the alternator quit charging. It would have quit charging when the MF blew but if you had a huge draw on the battery it would have blown the fusible link in the battery feed wire to the J block.
This leads me to believe that the alternator might still be shorting.
That's about all I've got until until I hear more from you.