Alternator ground question

[iwannadie]

Im trying to sort out some electrical problems that I wont go into here, just focusing on the alternator ground.

With the car off, alternator out and battery unplugged;

Using my multimeter set to continuity, I touch the ground plug at the Alt. and any ground (negative bat cable, ground under the fuse box, next to the fuse, etc). The digital readout shows .456 or around that, .4xx and the multimeter does not buzz.

If I test from the alternator ground plug to the Alt. fuse, the readout doesnt change and it buzzes.

Going from the Alt. fuse to any ground point, it again reads .4xx and does not buzz.

Everything else Ive tested using continuity, the mulitmeter always buzzes and the readout doesnt change. Is something wrong with my Alt. ground after the fuse or is that normal behavior when testing the continuity there?

If what Im doing even makes sense, Im trying to learn lol.

 

[90T04]

I think you have the "alternator ground plug" confused with the battery stud connection. The only ground on an alternator is the case itself.... Its grounded to the engine directly. You should have a low resistance reading from the alternator battery terminal to the alt fuse and to the battery positive. You should also have low resistance from the alternator case (when installed) to the negative battery terminal.

 

[iwannadie]

I think you have the "alternator ground plug" confused with the battery stud connection. The only ground on an alternator is the case itself.... Its grounded to the engine directly. You should have a low resistance reading from the alternator battery terminal to the alt fuse and to the battery positive. You should also have low resistance from the alternator case (when installed) to the negative battery terminal.

Ah right, battery stud it is then.

So, if the resistance is high (.4xx) then its got to be a problem with the wiring or what else is in between?

 

[iwannadie]

Ah, wait I was confused I guess lol.

Just tested the Battery stud connection to positive battery terminal, shows good continuity.

 

[90T04]

ok ya you got it figured out:icon_bigg

 

[jetjock]

While resistance testing is good for basic wiring checks it's pretty much useless for charging system work. What it comes down to is your meter is not capable of measuring the low resistances that impact circuit performance, especially in high current circuits.

Voltage drop testing is the way to go. I have yet to work on one of these cars that didn't have excessive resistance somewhere the charging system even though it appeared to be working and resistance checks were OK. Study up on that. It's a valuable technique that can be used to find all sorts of problems an ohmmeter can't.

 

[iwannadie]

While resistance testing is good for basic wiring checks it's pretty much useless for charging system work. What it comes down to is your meter is not capable of measuring the low resistances that impact circuit performance, especially in high current circuits.

Voltage drop testing is the way to go. I have yet to work on one of these cars that didn't have excessive resistance somewhere the charging system even though it appeared to be working and resistance checks were OK. Study up on that. It's a valuable technique that can be used to find all sorts of problems an ohmmeter can't.

Thanks for the info, Ill start reading up on that next