Bad Alternator ?

[PaulD]

Can an alternator cause 12V to read on the ground wire ?

[kris]

Originally Posted by PaulD

Can an alternator cause 12V to read on the ground wire ?

I have never seen it do that. What are your symptoms?

[PaulD]

It was one of THE oddest things I have ever seen. I was putting in a new battery, the old + terminal was ok but the neg term was trashed. I disconnected both terminals, pulled the old batt out and put the new one in. I reconnected the + term to the new battery, put the new neg term on and was trying to get the wires out of the old neg term. It hit the new neg term and sparks went flying, later one of the ground wires touched the neg term and more sparks. I thought maybe I had connected the battery up backwards. I drug out the trusty DMM and from the neg post of the battery to the disconnected wire coming from the frame it read like 13.x volts, I was like WTF. I disconnected each of the three wires coming from the + term and found out it was the one from the alt. I finally decided it was dorked up so I was just gonna get it running to get it to the shop. I left the alt wire disconnected and connected up my grounds, then I decided to see what the current draw was thru the alt wir with everything connected, it was only like 12 mA. I reconnected the alt wire thinking that was pretty normal and there were no sparks. Everything works fine now .... go figure

[kris]

Interesting. Is it possible that the alternator power cable might be pinched somewhere? This could maybe put 12v through the chassis. But then I suppose that it would be arcing wherever that pinch was.

[PaulD]

I looked and saw nothing where the wire was damaged or whatever. I just can't believe 10-12 mA caused those kinds of sparks

[FrankVtec88]

To the furthest of my knowledge, 12V should be the reading on the ground wire. You are flowing electrons to the ground, and pretty much the ground is just like another component in the line of many components in your car's electrical system. Therefore, if the system runs on 12V, the voltage at the ground should remain the same. But I'm not an expert, so someone please verify.