Fried alternator; truck won't start.

[Norcalsully]

After suffering a bad ground, I fried the positive lead to my alternator. Full melt down: smoke and melted wire coating. I replaced the alternator and positive feed. The truck won't start, I turn the key and get absolutely nothing. Battery has juice, starter has juice, line to the alternator is hot. My '70 step side definitely needs a new harness but in the interim any ideas to get her started?

All help is definitely appreciated. Thanks?

['68OrangeSunshine]

Did you replace the Fusable Link from the Positive cable to the passenger side Fender Terminal? Usually there's only one, but my '71 GMC Jimmy has another Fusable Link on the drivers side too.

[vdawg]

http://www.madelectrical.com/electrical-tech.shtml

[Jurassic-1]

Another overlooked area is the junction block next to the battery on the fender. The large red wire feeds the main fuse box. I had a similar problem. My truck would not always start especially after it was driven on hot days. I could jump the starter and it was good. I cleaned the connection at the junction and it works great.

[leftybass209]

You had a bad ground, fried some wires, and admit you need a new harness; it's time to get out the multimeter and take your time checking and looking at everything.

You dodged a bullet that your harness didn't catch on fire and cause more damage. Personally I'd take that as a hint that instead of rushing to get it up and running again with more potential fire hazards, to run over it with a fine tooth comb to prevent your whole truck from looking like that toasted positive lead.

You can look into m&h wiring. They create factory look and fit harnesses with upgrades if you need. You can purchase a harness at a time to lighten the load.y engine harness was fairly cheap, and modified for hei.It was a clean easy install that didn't suck my wallet dry. I refurbed the rest of my harness wires, replacing, soldering, and heat shrinking as needed. I have less than $200 bucks in my whole harness, and I'm confident it's solid and hazard free, because I looked at every single wire, from tip to tip.

Took about 12 hours.

Best of luck!

[67 chevelle]

I would say you had a short , not a ground issue ,, is the purple wire hot in the crank position ?

[cleszkie]

Originally Posted by 67 chevelle

I would say you had a short , not a ground issue ,, is the purple wire hot in the crank position ?

X2. If you lose a ground, current doesn't flow.

[MARKDTN]

Originally Posted by leftybass209

...You dodged a bullet that your harness didn't catch on fire and cause more damage. Personally I'd take that as a hint that instead of rushing to get it up and running again with more potential fire hazards, to run over it with a fine tooth comb to prevent your whole truck from looking like that toasted positive lead....

I could not agree more. You do not want to have a burnt-to-the-ground truck because you were too cheap to fix it right. Please don't just put a Band-Aid on this. 'Lectric Limited is also a good source for harnesses. They aren't cheap, but that is a nice looking truck. Do it right, do it now, and you will be much happier.

[Norcalsully]

Thanks for the replies. I pulled the trigger and got the American Autowire complete upgrade.

[Tork?]

Originally Posted by '68OrangeSunshine

Did you replace the Fusable Like from the Positive cable to the passenger side Fender Terminal? Usually there's only one, but my '71 GMC Jimmy has another Fusable Like on the drivers side too.

I had similar condition and it burned up the fusable link.

[ElKotze]

That AAW kit is really worth every penny. And you learn a lot about your trucks electrical system. Plus, with the step-by-step instructions it's a pretty easy job, just take your time. Good luck.

[legotech7]

Good post, I have a similar problem. My battery had some what low voltage after checking it with a volt meter. Charged it up, try to start it, and it cranked slow, I noticed some smoke from the engine bay, Yikes!..... rushed out disconnected the battery. I noticed that the negative wire from the alternator was fried at about a few inches from the mounting point. Ok , so I replaced the burnt piece with a new splice. Tried to start it but that neg. wire gets very hot. I traced the other side of the wire where its mounted, next to the radiator, cleaned the connections and tried again still gets very hot. Did I fry the alternator, or could there be another issue?... What am I missing? Would appreciate some help!......

Thanks.....

[Xeen]

I wish I had more experience with wiring so I could offer some good advice.

[VetteVet]

Originally Posted by legotech7

Good post, I have a similar problem. My battery had some what low voltage after checking it with a volt meter. Charged it up, try to start it, and it cranked slow, I noticed some smoke from the engine bay, Yikes!..... rushed out disconnected the battery. I noticed that the negative wire from the alternator was fried at about a few inches from the mounting point. Ok , so I replaced the burnt piece with a new splice. Tried to start it but that neg. wire gets very hot. I traced the other side of the wire where its mounted, next to the radiator, cleaned the connections and tried again still gets very hot. Did I fry the alternator, or could there be another issue?... What am I missing? Would appreciate some help!......

Thanks.....

Is this your alternator It's the only one I know of with a negative wire. It's the externally regulated stock type and should be converted to the internal type 12 SI.

[legotech7]

Here's a pic, you see the yellow wire I had to splice ti the ground. Thats the alternator I was using with no issues until now . A bit more detail,.... I just replaced the transmission the truck with a new rebuilt one. I took care not to disturb any wires around it. ( starter, etc.. ) but I could be mistaken. The only wire that is getting hot is that negative wire from the alternator. I did notice that there were no ground straps from the engine to the frame or the fire wall, nor did the trans have one when I took the old one out. Could this have been the problem? Or could this be a problem? Anyway I'm have the battery and the alternator tested tomorrow, but I was hoping to get some help here and see if anyone else has run into this issue... Again thank to all....

[CST10]

Originally Posted by Jurassic-1

Another overlooked area is the junction block next to the battery on the fender. The large red wire feeds the main fuse box. I had a similar problem. My truck would not always start especially after it was driven on hot days. I could jump the starter and it was good. I cleaned the connection at the junction and it works great.

Ditto on this one. Happened to me.

[VetteVet]

Originally Posted by legotech7

Here's a pic, you see the yellow wire I had to splice ti the ground. Thats the alternator I was using with no issues until now . A bit more detail,.... I just replaced the transmission the truck with a new rebuilt one. I took care not to disturb any wires around it. ( starter, etc.. ) but I could be mistaken. The only wire that is getting hot is that negative wire from the alternator. I did notice that there were no ground straps from the engine to the frame or the fire wall, nor did the trans have one when I took the old one out. Could this have been the problem? Or could this be a problem? Anyway I'm have the battery and the alternator tested tomorrow, but I was hoping to get some help here and see if anyone else has run into this issue... Again thank to all....

Your number one ground should be from the negative on the battery to the engine block because the largest current draw on the truck is the starter. This means that the alternator should not need to be grounded so you can pull the yellow wire off the alternator. If it runs to the engine block as an additional ground you won't need it. If it has a poor connection to ground you will get high resistance and heat buildup in the yellow wire.

It's also possible that you have a couple of blown diodes inside the alternator which are causing shorting issues to ground through the yellow wire and causing it to overheat. Do a diode check between the large terminal on the back of the alternator and the alternator body. If you read ohms both ways then the diode or diodes are blown and the alternator will have to be replaced.

[Xeen]

One thing I would suggest is head out to harbor freight and buy yourself a heat shrink wrap kit and a heat gun so in the future if you have to do any wire repair you can be sure it is done right.
This is inexpensive insurance against moisture intrusion and corrosion and as an added bonus it looks pro.

[bigmac73]

I use the liquid electrical tape , works good as well

[legotech7]

Thanks guy's I will double check my grounds... Vettevet, I will try your suggestion and remove the additional ground from the alternator and will do a diode test and see what happens, but I just took the alternator and had it tested at Advanced Auto, and it turned out OK, but could it still be working even if it fails a diode test? Would adding additional ground straps from the engine to the frame be beneficial or would it be too much?..... Thanks again...

[VetteVet]

Originally Posted by legotech7

Thanks guy's I will double check my grounds... Vettevet, I will try your suggestion and remove the additional ground from the alternator and will do a diode test and see what happens, but I just took the alternator and had it tested at Advanced Auto, and it turned out OK, but could it still be working even if it fails a diode test? Would adding additional ground straps from the engine to the frame be beneficial or would it be too much?..... Thanks again...

Yes your alternator can charge with a bad diode in it, but usually it won't charge at the full rate, and when you shut down the engine it will drain the battery. This does not appear to be what happened in your case if you replaced the yellow wire and it did not burn it up again.
Additional ground straps would be beneficial and you can never have too many grounds.

[legotech7]

Well, I think I solved my problem... I did eliminate the ground wire from the alternator, But added two new ground straps; one from the engine to the frame and another from the frame to the body... Boom, she started right up. I also noticed that my lights are brighter. I guessing when the PO replaced the engine he never bothered with the ground straps. Thanks everyone here for your help, I love this forum.......

[57larry]

glad you found the issues. good looking truck

[legotech7]

Thanks Larry, work in progress, but I love it..................