How do tell what the ouput of my alternator is? Thanks for any help.

 

Real simple test for this. First you get the engine running about 3000 rpms, then you get your hands good and wet. Firmly grab hold of the negative batter post, with your right hand ,and then with your left, carefully reach around the running alternator and push your finger on the output post of the alternator. Just kidding.

If your 1990 is stock, it is a 2g alternator. You can see an external fan right behind the pulley on a 2G. Think most of that year had 70 amps max. Some models had heavy duty systems. There might be a tag on the alternator showing the max output.

It is a lot easier to answer the questions if you give more info. Like year and engine size, and why you are asking about the max output. Got electrical problems? Thinking about loading up on lights or stero equipment? The plug connection on the 2G is a problem for many people, and has caused a number of fires. I would not load it any more that the factory load. Pretty simple to convert this to a 3G latter model alternator. Google will find you several good write ups about doing just that.

Good luck Frank

 

Thanks for the help Frank and sorry about the lack of info. The truck has a 302 in it and I am going to put a couple of driving lights and a couple of fog lights on the front. Will 70 amps be enough? I know I should at least go up to bigger wire for the lights right?

Thanks Kyle

 

I played around with an amp-probe to see how much my truck was actually using. Best I could tell with everything electrical turned on, and the rpm's at driving spped, I was using about 25 amps. The balance is available for whatever you need, but you don't want the alternator working at close to it's max ouput all the time. Since the lights won't be used all the time, and they won't be used in heavy traffic, when engine speed is low, the 2G should produce enough to do the job.
You really need to check the plug on your alternator. Any sign of loose connection or melting of the plastic around the metal connections, or any thing that doesn't look good, is a sign of an impending problem. Replacement 2Gs usually come with a new plug that is soldered into your harness, just in case.
Be sure and use a relay to turn your lights on. Heavy wire to the relay and to the lights, but you can use lighter gauge to do the switch. Don't foreget to use a fuse for each circuit. The wire gauge will determine the fuse size.
Here is a good article about upgrading the 2G to a 3G. And the graph at the bottom shows how many amps a new alternator produces at different RPMs. The alternator rpm is different that the engine RPMs. For example if you have an 8 inch crank pulley, and a 2 inch alternator pulley, at 1000 rpms on the engine, the alternator is spinning 4000
http://fordfuelinjection.com/index.php?p=75
Good luck Frank