Blown Alternator Wire

[CoachH]

I just replaced the generator in my daughters '54 chevy truck with a one-wire 100 amp alternator (Summit Racing® Alternators SUM-811001). It has the stock 235 motor in it. After installing it we tested the alternator and everything checked out fine. We took it for a ride today and it ran great. But when I pulled over to let her drive, it struggled to start when she turned the key over and before it kicked over it started smoking. I popped the hood and it fried the alternator wire. It was toast from the edge of the battery terminal half way up the wire towards the alternator. It was 8 gage wire as per the recommendation that came with the alternator. Anyone have ideas why it melted the wire? im guessing maybe something shorted it out by the battery? I saw a few sites online that recommend 6 gage wire for an 100 amp alternator, but the paper that came with it said 8 gage so i didnt think that could do it.

Anyone have any ideas?

Thanks

[mud.man.rj]

Is your truck electrical neg ground or positive ground, alt w be neg ground as newer systems. I'm sure your up to date w a neg ground system but just asking.
Mudman.

[mongocanfly]

could you tell if there was a dead short on the wire were it might be arcing on something?...looks like a hot to ground fried wire

[CoachH]

hate to say it but Im not sure. Im new to the hot rod world and until today I didnt know there was such a thing as a positively ground system. When I bought the truck it was converted to 12 volt. It still had a generator. is is possible it was still hooked up as positively ground? is there a way to check to see?

[CoachH]

Tried to find somewhere that it might have arc'ed but didnt see anything.

[mud.man.rj]

If your neg cable normally goes to the block then it's a neg ground system like you thought, so time to figure out what fried the wire, 8 over a 6 gauge would slowly melt the main wire under a higher load like say battery being mostly dead but not fry it like yours did, looks like a dead short or battery has a dead cell and alt is running wide open, have to start by making sure battery is fine first then check thru the wiring to make sure it all looks correct maybe even have to new alt checked at a shop last resort, could be a bad alt, prob not but have to start somewhere right.
Mudman.

[mud.man.rj]

One last thing that could happen if you had a poor ground wire, under sized ground wire or not enough proper grounds so pos wire w take all the load. Thing is your going from a prob 25 amp generator to a higher output alt, so need both wires, pos/neg sized correctly.
Mudman.

[joedoh]

that looks like solid core house wire. if it is, its not made for a high vibration environment and the insulation is not made for the temps underhood.

if its not, I can only reiterate to look for any areas where it grounded out.

[CoachH]

Thanks guys for the quick replies. Im gonna check for a short tomorrow. The battery is in one of those drop down battery holders, and it seemed to be very close to the positive battery terminal when I put it in. So I'll see if it shorted out there. I will also check the wire that was used. I bought it at a hardware store instead of an autoshop. Could that be it? I thought 8 gage wire was 8 gage wire, but maybe it should have been something specific to automotive needs?

[dsraven]

once you get the ground type figured and label the area near the battery for future boost starts etc, likely a neg ground if it was already converted to 12v, then check the foot pedal for the starter (you said stock so I am assuming here) to ensure it isn't sticking on and keeping the starter engaged for awhile after the engine starts. that can cook a starter pretty quick and cause a huge draw next time you use the starter. check the terminals on the starter while you are there. check the terminals on the battery to ensure a good clean metal on metal connection. make sure the battery is fully charged and have it load tested. nothing fries a new alternator quicker than an almost dead battery. a good idea to take the alternator with you to the parts store and have them check it as well. after a hard charge or misconnection you never know if the alt is still good unless you have it checked.

-check to ensure you have a good solid metal on metal ground connection from the battery to the engine block and truck frame and truck body. a large cable from the battery to the frame and engine block and a smaller cable to the body, enough capability to run lights power equipment in/on the truck and stereo etc. even take existing cables off and shine up the area and the cable end then install with clean bolt and a star washer between the bolt head and the cable terminal. then spray a little paint on it to help with corrosion or some electrical connection anti corrosion grease.

-check to ensure you have a good connection on the positive battery cables as well. if your battery is under the floor ensure you have sufficient cable size for the run of cable length and current draw from the starter.

-check to ensure the positive cable is not rubbing/shorting on anything anywhere from the battery to the starter. check all other wire circuits as well. look for melted or dripping cable insulation. if you have a trailer plug check that as well. all the circuits should be fused but you never know unless you wired the truck yourself. stick your head up under the dash and look around for anything that can rub, especially around stuff like wiper linkage, pedal linkage, door hinges etc. turn the aux circuits, like heater, lights and wipers on and check for large draws. do you have power door locks or windows that you may have used? a/c? wiring that runs under door sills or carpet-unseen areas?

-if battery is under the floor ensure it is secured well so it can't move around and possibly short out

-if battery is under floor check to ensure there is nothing that could move during the flex of the truck frame/cab and short a positive cable somewhere

-check to ensure the alt wiring is correct by manufacturers standards.

then, once all rewired and checked, try again. start it up and check alt output. it should charge at around 14-14.6 volts max. turn on all the accy and see if it keeps the voltage up. if you have access to a load tester you could apply load and see what the alt does for voltage and amp outputs. of you have a 100 amp alt you should get at least 100 amps from it when testing. some alts won't "turn on" until idle is increased so ensure you do that as well before starting your tests.

[1project2many]

There are two wires in the photo. Were both wires originally one wire or is that two separate wires? I'm looking at the area at the end of the melted section on the top wire. Was that spot laying on the positive battery cable or on a potential short like the exhaust manifold?

[CoachH]

Yes, it is one wire cut in half. We broke down on the road and I crawled under the truck to cut the wire off as close to the positive terminal as I could (battery is underneath so I had to reach up to get to it). It was completely fried. Then I cut it half way towards the alternator. Thats the part the is 100% fried. The 2nd half went to the alternator and wasnt damaged at the spot it connects to the alternator bolt. Its the section of wiring in the picture that is only half way burned.

[4544speed]

Just wanted to add my 2 cents. I agree with the advice you have gotten so far. IMO a good investment is the "how to wire your street rod" from Speedway motors. Best 8 bucks you will spend on electrical and making accessories/ lights work. It has 6/12V conversion info and alternator/generator info - not model specific. Copper wire is copper wire but one item that changes is the insulation on the wire and the other is the flexibility based on the amount of strands/size of the strands. You can buy tin coated copper (think welding wire) which is more resistant to corrosion. As for the lugs, try to crimp them properly. Don't just lay it one the ground and flatten it with a hammer. If you don't have crimpers, try to emulate a hex crimp which is the most effective. I do agree this looks more like a shorting issue but you may have fried something else so you may need to troubleshoot.

[_Ogre]

ogre has a similar 1 wire alternator hooked up with 8 ga wire for the last 30,000 miles, i don't think wire size is your issue
from the looks of the wire insulation it was a short issue starting at the point of good/bad insulation
try to reinstall the old wire without connecting it to see where the good/bad insulation point was

[Russell Ashley]

Originally Posted by _Ogre

ogre has a similar 1 wire alternator hooked up with 8 ga wire for the last 30,000 miles, i don't think wire size is your issue
from the looks of the wire insulation it was a short issue starting at the point of good/bad insulation
try to reinstall the old wire without connecting it to see where the good/bad insulation point was

All information above is good, but I think this is the right answer in this case. I think you will find that it was melted through by touching the hot exhaust manifold or was pinched between two metal parts. I would use automotive wiring this time.

[franken]

A fusible link at the battery side would have made this a non-issue, other than figuring out the FL cooked, and finding the short..

[51chevytruck]

The site "Mad Electrical" has a ton of good information on wiring.

[mr48chev]

As I usually do more often than not I have to agree with Ogre. That wire shorted out just about where the end of the burned part is. You will find a spot in that area where it arced to metal. In that short period of time that means it was laid against something that got hot (exhaust) or pulled over something with a sharp edge that cut into the insulation.

Add to that you absolutely need stranded automotive wire rather than single strand house wire. Single strand won't handle the vibration. Add to that it would be wise to put some R type wire holders every so often to keep the wire from moving around and rubbing on something.

[CoachH]

Thanks for all the information!! I fairly certain we narrowed down the problem to the connection to the main batter terminal. The drop down battery box has relatively sharp edges and Im guess the wire rubbed on that and ultimately grounded out.

I've heard mixed opinions on whether you should wire the alternator to the positive bolt on the starter or directly to the battery. Is it ok to wire it to the starter?

[mongocanfly]

either way will work...

[_Ogre]

ogre moved the battery behind the pass seat
it was a lot easier to hook the alt to the starter
same 12 volt +

[mr48chev]

As Ogre said connecting it to the stud on the starter solenoid is fine and preferred actually.
That is where the power feed to the rest of the truck should be tied in anyhow.

Personal experience and not all good says that the less wires you have running to the battery under the floor the better off you are.