Had a short, now electrical system keeps shutting down

[G-Rob]

Hey guys, I was working on my car late one night, did a bonehead move and forgot to disconnect the battery and was removing my one wire alternator and it rotated off its bracket and hit the valve cover. So the positive terminal hit the valve cover and caused a short. Sparks flew, and the insulation on the wire leading from the junction box to the battery caught on fire. Got that put out and replaced the wire. Haven't hooked up the alternator yet as it is part of a bigger project that I am undertaking.

Once I replaced the wire, I wanted to see if the car had power from the battery. It did but as I put load on it ie. headlights or starter motor, they would operate for about 1 second and then all electrical shuts down. It will eventually come back on after a few hours to full power, but will then shut off again if I put high load across the system.

i have no idea what this could be. It's almost like a safety switch of circuit breaker is triggering because I have been through the wiring diagram and cannot for the life of me see anything that would shut the entire system down.

All fuses in the fuse box are fine.

I'm wondering if I fried the battery and it has a safety switch in it. I just don't know what else it could be. It's not behaving like a short per se, more like a safety system.

Any help would be appreciated.

Thanks,

Rob

[G-Rob]

Forgot to mention its a 1969 Camaro.

[G-Rob]

Okay so spent more time with the car and started adding loads until I had all the lights including the headlights on. Everything seemed okay. Then I shut it all down and the motor turned over.

I am going to clean the battery terminals and check all wiring for shorts because I really don't want this to re occur on the open road. But I still don't know what the root cause is of this. Any suggestions on wht to look at would be appreciated.

[sccacuda]

The dead short of grounding the alt is the same as laying a piece of metal across the battery terminals. You are trying to fully discharge the battery, at whatever amps it had, to ground, instantaneously. The positive cable from the alt carried WAAYYY more amps than it was rated at and melted, but it was trying to return to battery ground, so the ground from the engine/chassis to the battery ALSO carried that load. Might want to check all your ground wires.

[G-Rob]

Thank you. I will check them further. I checked the main one from the battery to the block and it appears okay.

[astroracer]

Craig nailed it. I would pull the main grounds and replace them even if they look alright. Running that kind of current through a small cable will tend to "cook" the wiring inside. Even if it looks okay it can create a large resistance in the wire itself. At least check the resistance in the cable with one you know is good.
Another thing to consider is the battery itself. Shorting it like that puts a tremendous load on the battery cells. They are trying to dump ALL of their charge at one time which creates a lot of heat and gas discharge. I would check the battery cells to verify you haven't lost one or two.
Mark

[G-Rob]

Okay I will attempt to replace the main grounds. As for the battery, I have checked it with a multimeter and it is putting out 12.6v but that said, I am wondering if I fried it myself.

The whole event probably lasted about 5 seconds but as you know time slows down when you are in full crisis mode so who knows how long it really lasted.

Thanks for the continuing advice.

[G-Rob]

Just tested the resistance of the main ground from battery terminal to engine block and it read between 0.0 and 0.1 ohms.

[sccacuda]

Just tested the resistance of the main ground from battery terminal to engine block and it read between 0.0 and 0.1 ohms.

Your testing large gauge cables with micro volts from a DVOM to get a resistance reading. That works to tell you continuity. A voltage drop test, and if you have a shunt for you DVOM, an amp clamp might be more accurate to let you know the circuits ability to handle load. Make sure you are loading the circuit (headlamps on, starter engaged, etc...) when testing. Don't forget that these test should be performed on the ground circuit as well. People always forget that 12v DC systems need power and ground to be complete circuits and the both sides of the system handle the same loads. Whatever size the power wire, the ground wire must be the same gauge.

[G-Rob]

First off I appreciate your comments Craig as this was my concern on the main cables - even though they read 0 ohms with a very small current, what would they read with normal loads - so I will test them with a load on them.

Second, the wire from the alternator to the junction box had it's insulation melted in several places in addition to the wire from the junction box to the positive battery terminal. I have replaced both wires but did not get the car buttoned up for testing yet. That will come this evening.