stumpshot

I've been having a run-on problem on the 75 for a week or so. Pull the alt wires and it shuts down. This is on a brand new, not rebuilt, alternator. The old alt was ok, just old. Since this was a new unit
I didn't have to core. Took the new alt back, told them it was back feeding and they gave me another one. Took it home---no good. Still running on. Put on old alt---problem gone.
Try returning this new one another time? Don't have any proof it's backfeeding except what I tell them. I really don't mind changing alts but how many chances do you give these guys?

croaker

1 Your old one connects the same way?

7T1vette

Quit buying junk at "The Zone".....

stumpshot

Croaker. Yep same as it ever was.
Other guy. I don't buy parts at "the zone". This is a reputable, natuonwide parts house. The old alt I got from them is 7 years old and still works like a champ.
Thanks for the help.

BP 77

I purchased one about four years ago and then replaced it twice under warranty. Current one is three years old now. Also purchased from a national parts retailer.

until you get a good one is my answer

juanvaldez

Is it a new Chinese alternator or a new AC-Delco alternator?

The13Bats

How many in a batch can be bad? All?

GUSTO14

If it were me and I had a functioning alternator, I would purchase a rebuild kit for it and rebuild it myself.



The only things that typically wear out on a functioning alternator are the bearings and brushes. Shouldn't take more than an hour to change them out, 30 minutes if you've done it before.

Good luck... GUSTO

TimAT

Some MSD ignitions need a diode in one of the wires to the alternator. MAybe you need one.

stumpshot

Thanks for all the replies and advice! I'll check into a diode and I think I will kit the new one just for grins and see what happens.
Thanks again.
Stump

JayRay

Bad fusible link?

Metalhead140

As above, if you run and msd (or some electronic ignitions) you can have a run on issue if you don't have a diode in the lamp feed to the alternator. I had to do this on my Vette when I put in an MSD dizzy/coil/6al in place of the hei. I also had to do it on my f250 when I installed an electronic dizzy in place of the original points dizzy, and fed the ignition from a relay.

terrys6t8roadster

Jegs sells a rebuild kit for under $40 , it has everything in it. Part number 10140. T

MotorHead

Yup this is the problem, pay 50c for it and use the forty bucks on something else

7T1vette

Very interesting. Diode prevents 'back-feeding', I assume.

Do the MSD installation instructions describe the need for that diode? I would think that little 'issue' would have a big, bold RED note box on the instructions!

Kacyc3

It doesnt do this with the old alt. installed, just the new one correct?

TimAT

Yes they do-- that's how I found out about it.. And it stated that it was not needed in all applications.

theandies

Diodes only let current flow in one direction and not in the other. Think of it as an electrical check valve.

I have an MSD 6al box but I don't remember installing a diode and I don't have the run-on issue. My 6al has been installed for 15 years. Good to be me I guess.

OP - I'd just rebuild what you have. Cheap and easy.

pacecar620

The diode only allows current to flow in one direction.

buns

The diode is usually only required if you have a charge light indicator, as opposed to an ammeter or a voltmeter.