atb

This is on the '79 track car.

12v at starter and alternator, but not at the jumper post under the hood.
Tom M. suggested running a jumper cable from the lug on the alternator to the jumper post and the starter cranked over fine with a twist of the key.

Its such a large gauge wire that I find it hard to believe that it is broken through. I'm thinking maybe it's just shorted out?

Anyone experience this situation before? I'm presuming its a single heavy gauge wire that's a straight shot from the alternator to the jumper post, but the wiring diagram is a little ambiguous. It shows a single line coming off the alternator and then splitting into three, but doesn't specifically show the jumper post.

Thanks for any help.

jcorenman

No, it's got to be broken or open connection somewhere... a short to chassis would dump the battery current to ground, enough amps to melt the cable and make lots of smoke. It is a direct connection from the alternator to the jump post, part of the cable that comes out through the timing-belt covers on the driver's side. There's got to be a problem somewhere along there.

Good hunting!

dprantl

Isn't this the harness that goes through the timing belt on the driver's side and across the front of the engine to the jump post? I would think if it shorted to ground, it would only be for an instant as it would try to become a welder until it melted a break.

Dan
'91 928GT S/C 475hp/460lb.ft

Lizard928

Most likely that you have a break at the alternator.

GlenL

I suggest it's corrosion at the ends. Between the connector and the cable or the connector and the stud. Very hard for the cable itself to go bad.

Dave928S

I've pulled that one out on my 82 and I'd be thinking a connector (or very close to the end) issue too.

Tom. M

It's not unlikely that it could be broken....here's a pic of mine before Chris F rebuilt it....the frayed part was right where it went through the tbelt cover...excitation circuit, starter solenoid wire, amongst others were affected...

atb

That is downright ugly Tom.
I'm trying to avoid pulling and replacing the wire. Maybe, if there is a break, I can soldier and shrink wrap. I'm going to try to get out there for a couple of hours in the late morning.
Would very much like to get this beast running so I can get it caged.

Alan

Replacig the wire is the best bet - unless the issue is at an end and you don't have to shorten too much. Do not repair a break in the middle of the wire - bad idea...

Alan

IcemanG17

I vote for the wire being busted.....

underdog928

I had a similar problem during my 2010 summer WP/TP/Intake refresh project.

Here: https://rennlist.com/forums/928-forum/568589-frayed-cable-how-do-i-fix-this-fixed.html

The combination of soldering the frayed wires and wrapping them in self vulcanizing silicone tape seems to have done the trick. It's been over a year and a half and no problems. (that I know of)

Once you take the wiring harness apart and find the problem, you might be able get away with an easier fix than replacing the entire cable harness.

Strat_928

I was going to replace that action in mine myself after reading it can be source of problems from time to time. I was going to replace it with a larger gauge at the same time. But I bought too short of a length and need to re-measure.

It is not that expensive, so I agree you should replace the wire and put new ends on and be done with that section.

atb

Idiot maneuver. Took a hard look at the rear of the alternator when the car was in the air before getting started this morning and saw the jump post lead was on the field winding terminal. Moved it over and the car cranked right up. Total rookie move. Would not have believed it had I not seen it with my own eyes. Sometimes, I wonder what I'm thinking when I work on my car.

BTW, thanks to everyone who volunteered responses - and for presuming that I had done it right the first time.

Bill Ball

That's not even near the middle of the screw-up scale. Nothing burned up or exploded.

dprantl

And not even a blood sacrifice...

Dan
'91 928GT S/C 475hp/460lb.ft