I have my antilock light on, and some very low voltage at idle. When the truck is at high rpm's the light pulses, and so does the speedometer. The voltage is abnormaly high then as well.

I'm not sure if the alternator is dying, or there is some other voltage regulator type thing going on, as I'm at work and have not had the chance to check it out.

Anyone had this happen?

There are three different amperages in the available alternators, does anyone know which will be in my 91 250?

(I posted this in help! as well) My apologies to anyone who might have had to read it twice.

 

my service manual says theres only a 120amp for the 91s... there is an external voltage regulator in the center of the firewall. think autozone will test your alternator for free and if thats good you probably need a regulator.

 

I have an 89 w250. I was plagued with electricl problems & dash lights freaking out & wild fluctuating voltages. The problem was bad grounds all over the vehicle. I ran jumpers everywhere & all the problems went away & never came back.

 

I finally chased the problem down. The thing that looks like a voltage regulator is an SMEC,(single module engine control). This does the voltage regulating on 91's. They switched to a PCU in '92.

They suggested checking all of the grounds and connections, and sure enough that's what it was. I love free fixes!! Thanks for your ideas guys.