I had my 91 F 250's electrical system checked the other day after I had to replace the starter and both batteries. The check showed 122 amps output from the alternator. I pulled the alternator today and had it checked at two different place; both times it cam out ok. I also had the voltage regulator checked and it came out ok. What could be causing this? I probed the wiring from the alternator to the starter relay and over to the glow plug controller and it all ohm'd out to zero. Where else should I look?

Thanks in advance.

 

Put it all back together, and check the voltage on one of the batteries with the engine running with a good voltmeter. You should read 14-14.5v. If it's much higher than 15v, then you are over charging, and the first thing I would check is to make sure the regulator has a good ground where it's bolted.

 

If you have a 125 amp alternator, 122 amps would be good.

There are several different ways to test alternators.
And there are many different amp ratings available.

If they were testing to max output, depending on the alternator that is probably a good output.

When you have to worry is when you get an answer like this from the guy testing the alternator.

Well your batteries need charged.
The alternator is putting out 14.3 volts and 7 amps at 2000 RPM.

Then you have to reply, well the alternator is a 150 amp unit, so if the batteries are low, why is it only putting out 7 amps?

All the best test equipment in the world is worthless if the person running it don't know what the test results mean.

 

Thanks guys. The alternator is putting out between 14 and 15 volts and 122 amps. The alternator is a 100 amp unit. I will re check the ground at the voltage regulator. One other note is I had to replace both batteries and the starter burned up. Once I replaced those then I had it tested. Another issue is the trans. I have to take it and have it diagnosed because it went out. Any chance there is a problem with the electronics in the trans and it's causing this?

Thanks again!