Alternator ground wire insulation melting

[NathanR]

This can't be good.

Removed alternator because I'm planning to install a new VR...

[clarkd]

Possibly brittle insulation and rubbing resulted in hot and ground wires making contact.

[NathanR]

The whole length of the wire is the same condition, fwiw.

[zippy_gg]

It looks like the hot wires harness has been taped up, which in addition to your melted ground wire would make me suspect a short somewhere.
Can you remove the black tape and see what is under?

[HawgRyder]

Picture illustrates the difference between a ground WIRE and a ground STRAP.
I have always believed in ground straps...they just carry more current....and if the rest of the circuit is correct...they will carry all the amps used in the system.
For your case..I agree...check under the tape...also...check the ends of the red wires...are they just crimped...or crimped and soldered?
When dealing with electrical problems...always go big...if in doubt...make the wire bigger...make the connector cleaner...make the connection tighter.
Good luck
Bob

[timmy2]

Just an FYI, I install a #6 instead of the #8 in the replacement engine harnesses I build.
I see a lot of very crispy main leads on old harnesses.


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[NathanR]

That wire isn't terribly thick. I'll peel the tape back and see what I can see. Timmy2, did you mean the other way around? Wouldn't the lower number be thicker?

[timmy2]

Yes, I typed the wrong number. The Porsche cable is actually equivalent to a number 8.
I'll edit my post.
Thanks. Good luck finding why that cable is/was carrying so much current. I agree with zippy_gg,
probably made contact with the red cable at some time.

[HawgRyder]

Another thought...have you recently given someone a jump start?
If your motor is running at the time he turns his key....the majority of power will come from YOUR alt!! (law of voltage).
When jumping someone....by all means hook up and give them a 5 to 10 minute chrage if possible...but before he tries to start his engine...TURN YOURS OFF!!!
This way the power to boost him will come from your battery...not your alt.
Bob

[Marc Bixen]

We've seen this a few times before at the shop. This is typical of the results from hooking up jumper cables backwards. You're close HawgRyder. It only takes a couple of seconds or less to get this result. I'd remove the ground strap, body to trans and body to chassis and clean the connectors and surface with scotch bright, and replace your battery as well as the alternator. Also while you have it apart, we always solder the wire connectors for reliability.

[timmy2]

The theory of a bad boost is possible, along with the dead short of the cables.
The fact there is tape on the harness that shouldn't be there, leads me to believe the damage may be old.
Peel it off and take a good look at the red cables.


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[NathanR]

All great suggestions -- will check the taped area for sure, and refit a larger diameter wire/strap. The lug on the alternator side is quite small though. May have to think about that.

If the damage was done by a bad jump, it may have been before my ownership as I don't recall ever having used this car to jump another. No telling how long the wire has been like that.


Thanks again!
Nathan

[RDM]

Originally Posted by timmy2

The theory of a bad boost is possible, along with the dead short of the cables.
The fact there is tape on the harness that shouldn't be there, leads me to believe the damage may be old.
Peel it off and take a good look at the red cables.

timmy2,

How many wiring harnesses have you built to correct this problem? Or is this sort of damage repairable?

[manbridge 74]

Originally Posted by NathanR

All great suggestions -- will check the taped area for sure, and refit a larger diameter wire/strap. The lug on the alternator side is quite small though. May have to think about that.

If the damage was done by a bad jump, it may have been before my ownership as I don't recall ever having used this car to jump another. No telling how long the wire has been like that.

I like to use GM (the horror!) ground straps from ye olde junke yarde. The ones from body to frame are short, braided, have small ends, and are plentiful. Also, consider using star washers on all grounds between body/case and ring end . Many more contact points for current to pass through.

[Marc Bixen]

The factory ground strap costs $6.16 pt # 911-612-233-00. Not worth fabricating, I keep one in stock.

[wwest]

Alternator output is self limiting, 90 amps...

Reverse install a fully charged battery or reverse jump a discharged battery and the alternator diodes will be forward biased, TONS of current flow.

[NathanR]

I unwrapped the tape and the big red wire's insulation has crumbled and fallen off.

Anyone know where this wire goes? It's got be either the alternator, the battery, or the fuse block, right?

[timmy2]

NathanR,
The large red cable goes directly to the starter main terminal and from there directly to the battery. Looks a lot like there was apparently a dead short to the ground cable at some time.
The smaller red wire goes to the 14 pin connector at the fuse panel.

RDM, (Dru)
Lots... these wires see extreme cycling in heat and cold etc. after 25+ years they are brittle and fragile and corroded. A number of people contact me after a motor drop and a good inspection of their engine wiring...
Building SC and Mid Year Engine Harnesses

[RDM]

If I had to guess (and I do, since I don't have any Carrera manuals), I'd say the fat one goes to the battery and the thin ones go to the fuse blocks. This end goes to the alternator

[RDM]

Originally Posted by timmy2

RDM, (Dru)
Lots... these wires see extreme cycling in heat and cold etc. after 25+ years they are brittle and fragile and corroded. A number of people contact me after a motor drop and a good inspection of their engine wiring...
Building SC and Mid Year Engine Harnesses

My engine is on my garage floor and I'm trying to decide whether or not a new harness is in my future. Yes, I think about you a lot!

What level of disassembly is necessary to install a new engine wiring harness?