I have a 92 F-150 Supercab V8 5.0 w/AC. My alternator gauge is jumping around. Drops to 10 at idle, goes up to between 12 & 14 when moving w/AC, snaps to 14 wo/AC on. Battery is ok (12V). Had it checked and I'm told it's ok.

How do I find out what amp rating I have? Parts store has several to choose from (from 70 to 99). And how do I know if the regulator is with the alternator?

Thanks

 

Read the Batt...with and without the truck running...

 

You will either have a 75 or 80 amp alternator, regulator should be internial unless someone has rigged it otherwise and look like this on the back.

 

I'll look at it as soon as I can. Thanks for the help.

 

An abnormally low curb idle has the same symptoms but would clear up after increasing engine RPM just above idle.

 

Do you have a multimeter? A voltage drop can be performed between the battery post (not the clamp, so it can be tested at the same time) and B+ of alt. to ensure alternator cable has a good connection to the battery, as illustrated below.

 

 

Wow!! Good stuff. I will try this when I get home today.

Thanks again