Holy Melting Ground Strap!

[BoxDaddy]

My buddy finally got his CUCV that he always wanted and it is awesome.
It is a retired fire department truck from a local rural department.
It seems to be in excellent condition.
When he got it home from the auction, we charged up the batteries and it fired right up.

after warming up for about 30 min. and driving a total of about 10 miles, it suddenly turned off.
when it stopped, we smelled burning and immediately pulled the keys and disconnected the batteries.
The negative cable going to the body from one(front) of the 2 batteries was smoking and melted, the fusible link going from the driver side alternator to the small distribution block on the drivers side was also melting.

after replacing the ground strip and fusible link, we can't get the batteries reconnected due to major arcing and sparking.

we inspected all the battery cables and fusible links, they all look good.

ARRGGGGGGG!!!

Someone help! Please point out the obvious problem I'm surely overlooking.

 

[4bogginchevys]

compare the wiring on your alts to the schmatic, i bet the problem is there

 

[BoxDaddy]

24v Diagram

I have the FSM for the civilian models. I'm familiar with the 12v 350s and 454s, but this is the 1st 24v 6.2 I've been lucky enough to play with.
I believe that the wiring is correct, because it was running, and running strong.
That's why I'm thinking that a wire has worn thru and is now grounding out.

What is the solenoid type thing that pops out of the grill on the passenger side?
It has some high current wires running to it...
any components that could cause something like this when they fail?

 

[srodocker]

how much you win it at auction?

 

[POOR WHITE BOY]

Sounds like a bare wire grounding out some where

 

[DirtMagnet]

Do the batteries test OK?

 

[ralbelt]

On passanger side of grill is the slave port, used to jump a dead vechicle from another 24V military vehicle.

 

[Crash_AF]

Can you post some pics of the damage? Might help with diagnosis.

As was posted earlier, the thing on the passenger's side is for starting dead vehicles without opening the hood. The high current wires run directly to the firewall terminal busses and there are no components in the connector that could fail unless it is physically damaged.

To melt the negative cable at the core support, it sounds like there is a dead short in one of the high amp wires. There are only a few of them in the truck. The two that are not immediately noticeable are the slave port and the starter feed.

You should pull off the cables at the terminal block and check them with an ohmmeter to find out which one is shorted to ground, then trace it back to the problem.

Later,
Joe

Edit: Just to make sure we're on the same page, is this truck still 24V or has it been converted to 12V?

 

[BoxDaddy]

good deal?

how much you win it at auction?

I believe he got it for 1100-1200.
Sounds like a smoking deal to me...
Did he do good?

 

[BoxDaddy]

Still 24v

Just to make sure we're on the same page, is this truck still 24V or has it been converted to 12V?

It's still 24v, and he intends on keeping it 24v.
Any reason not to keep it 24v?

 

[Scarecrow1]

Is there a possibility the alternator is over charging and causing the melting . I would put a volt meter on it to be sure ....

 

[Somemedic]

Follow the starter cable from the battery down to the starter. Had the same thing happen while I was on the move. Did some welding... bad bad bad...

 

[BoxDaddy]

Good responses! Thanks! Keep em coming

I'm planning on testing both alternators and taking the multimeter to the starter cable this evening to eliminate all those as the possible gremlins.

Keep the brainstorm going, anything else I should check while I'm at it?

I will post my progress... and hopefully the cure this evening

Thank you all for all the helpful responses!

 

[4bogginchevys]

hey bud, I couldn't open the "diagram" you sent me because of some pop up blocker or some thing.....hope it wasnt important! I would un hook the slave cables to rule them out first. In my old 79 civi truck I had the same ground melt off, the battery jumped up and welded itself to the bottom of the hood when I went over a bump.......not the same scenario i'm sure but your current battery hold down situation might warrant some scrutiny. keep us posted!
BTW.... check the ground strap on passenger rear of engine, that one may have burned off too.

 

[BoxDaddy]

I knew it had to be something stupid!

There was apparently some sort of a 24v accessory mounted on the rear of the truck.
I know this because a super heavy cable was zip tied along the frame all the way back.
Whatever it was back there was long gone, and the cable was crudely cut and setting on top of the frame. While we were bouncing around on a dirt road, it grounded out and welded itself to the underside of the bed!

Alternators tested good, but one battery was toasted

All better now. Cable removed and all damaged wires replaced.

All except for the fusible link going to the drivers side alternator. What size link do I need to put in there?

Thanks again for all the help!

 

[4bogginchevys]

I dont think you can buy fusible links like that anymore......but you can buy fusible link wire in the proper guage per application, cross the rating on that to an inline fuse and i bet that would work.....glad it was something dumb!

 

[BoxDaddy]

I read somewhere that you're not supposed to use an inline fuse in place of a fusible link.

Anyone know why?

If I could use one wouldn't it have to be something huge like 125A to handle the spikes from a 100A alternator? (I don't even know if they are 100A, excuse my ignorance)

I know there's an electrical guru out there who has some answers. Come to the rescue!

 

[Stan Leschert]

Fire Dept... fitting! Check all of the 24 V cables for abbrasion. That would be the first place to look for your impromtu arc welding. Fusable links are still available and never try to replace them with a fuse or circuit breaker. They were designed for very different jobs. If that branch of wiring is no longer required, just disconnect it until you find a need to restore it. Just make sure that you label it. Sorry about the battery, Mil spec ones aren't cheap. Check the TM for the right size of F/L. GM should still have some stock.

 

[BoxDaddy]

Found a source for the fusible links.
The alternator needs a link that goes from 8ga to 12ga.
Tonight she will be back to 100%.

 

[BoxDaddy]

All better
Thanks for all the help!