why is alternator wire melting? (1 Viewer)

[cruisermedic]

easy answer its getting hot. not so easy answer is why. so i been having some trouble starting my 75 40 with the original 2f. i had been using starting fluid on the coldest days and it was ok. would run fine once started and warm. well now even on warmer days i need it. so i decide to change my cap rotor plug wires and the coil....spark appeared to be weak. well still trouble starting. bogs way down like not enough juice in battery. battery is a large interstate only a few months old.tested out at 10 volts. while i was craking my brother in law notices smoke from the back of the alternator. the small wire that appears to be a ground is very hot and the plastic end is softening and turning black. this should be a ground correct. right now its is running straight to the neg terminal of the battery. prob not correct. im am trying to fix things as i find them. any idea as to what this wire size should be, should read, and where it originally ran.

thanks, steve

 

[Mark W]

Never seen a ground wire to the alterrnator.

This vintage rig should have two wires from the regulator going into the back of the alt plug. A single heavier wire from a post on the back of the alt carries the output of the alternator. no ground wire.


Mark...

 

[FJforty]

Disconnect the alternator from the rig. Put a charger on the battery and start it up. The goal here is to see how many problems you have. A charger on the battery should keep it around 13.5 volts.

 

[Toyo FJ40]

Is it smoking when you are cranking the starter? Your engine ground might have a bad connection or even missing. There should be a large cable running from the engine to the frame. On my 74 it runs from the starter mounting bolt to the frame. The other thing could be the battery to frame cable has a bad connection at the frame and the system is grounding through the wire from your alt to your battery ground.

Pull the smoking wire off your battery and see if it will start.

 

[cruisermedic]

the wire is on the back of the alternator it is a small wire with a plastic harness. it is melting right at the harness where it plugs into the alternator. it appears that it is only getting hot when the rig dont want to start right away and longer cranking happens. i changed th coil cap rotor and plug wires, should have got new plugs cause the 5 and 6 were definetly wet and nasty. cleaned and checked gap and re-installed. rig fires up instantly. let run and check the wire no warmth felt. alternator is putting out steady 14 volts. and battery seems to be holding as well.

will check ground strapos when light out and can see better. freaking cold here in michigan right now.

thanks for the info. ill update asap.
steve

 

[Pin_Head]

There is a stock ground wire between the voltage regulator and the E (earth = ground in the US) terminal of the alternator. If this melts it usually means that the ground strap between your engine and the frame is missing or has a bad connection. That can also explain why you are having trouble starting.

 

[Mark W]

I would have to look int he schematics to claim that I really remember that this is a ground to the regulator. But I think I agree with you.

And the lack of a ground strap sounds like the winning answer to me too


Mark...

 

[LAMBCRUSHER]

I've seen a ground cable w/ no visible damage or exterior corrosion be bad. No continuity between the ends of the cable- corroded inside out! Had me stumped for a couple of days. I agree, look for grounding issues upstream from you alternator.

 

[nspctr1]

Yep, when I finished my 3 year resto on my 75 I had a little trouble starting it. Turned out the ground cable from the battery to the frame was bad. Externally you couldn't tell that anything was wrong with it but when I took it out to clean it up and check the insulation for scrapes it just fell apart in 2 pieces. Kinda weird...

 

[Pin_Head]

I would have to look int he schematics to claim that I really remember that this is a ground to the regulator. But I think I agree with you.

...

This E wire is white with black stripe and is present on all stock cruisers with external voltage regulator that I have looked at. It is also shown on all the schematics, but on the early schematics ('71) it isn't obvious that it is a ground. On the later schematics, it is explicitly shown as a ground wire. There are very few ground wires on cruisers, but they are all white with black stripe. Apparently, Toyota thought that the ground between the alternator and regulator was so important that they didn't want to rely on the chassis attachment as a ground. If the chassis ground is good, the VR and alternator will work fine without the E wire, so it is redundant. If the ground strap between the engine and the frame is missing or bad, the E wire is often the best current return path for the starter cranking wire, which is why this wire is frequently found smoked.

 

[cruisermedic]

ok so rig ran afew days and then just lost it again. got to the point that the battery seemed to be dead and the thing just cranked so freaking slow. battery tested good. checked ground strap. bad. replaced it with nice new big wire with clean ends on newly scraped engine and frame. crossed fingers....turned key.......she cranked over faster than ive ever seen. fired up almost immediately. ran it a bit and sounded to be smoother. parked it out side and let it sit till the temp dropped and drop it did. got down into the single digits and i thought for sure id not get a start but i pulled the choke and turned the keyt and it fired right up. been running great for a ferw days and no problem starting. amazing how important a ground strap is and what it effects.

thanks for the help,

steve

 

[LAMBCRUSHER]

Yeah, funny how circuits need to be "complete"! I beat my head on the fender of my old ford for a day and a half trying to figure out that one. Lesson learned- when doing things w/ electricity, you can't always use your eyes to see. (which is good, because I am a color blind electrician!) Good work on that BTW.

 

[nattybumppo]

Thanks for this thread. My 77 has been doing the exact same thing. Time to look for the missing ground. Lesson learned: just do what "Crash" suggests.