lights pulse bright and dim while truck runnin?
 

while the truck is runnin even after it warms up the dash light, head light marker light and even the lights in the radio pulse at any rpm. checked power at grid heater and there is no power goin to it so its not cycling on and off. new battery have clean conections voltage regulator only a year old and alt is only 4 months old. the voltage gauge has slight movement in it. grounded block to firewall block to frame and battery to frame and block. any one got any ideas i could try

those regulators are junk. i keep one in the glove box all the time.

yeah mine does the same thing. Where is the regulator even at?

It should be on the fire wall on the passenger side. that is where it is at on mine anyways. That sounds like it is your problem

That and the body ground is crap on these trucks. Replace the ground wire from the battery to the core support a good heavy gauge wire.

when in doubt ground it out I learned that the hard way :)

i have a 91 too and my is doing the same thing where exacty is it located?

I replaced my alternator with 1 from PA performance, internal regulator and bolt up.
voltage is rock steady now.

the reg is usually on the fire wall just above the rear valve cover , 2 wire connector with hold down spring , unplug the connector and lights will dim but will be steady , if so reg is junk

I had a similar issue and then went through several regulators. I even replaced the Alternator and crank sensor in pursuit of my issue. Never did get it truly fixed, but at least it charges again.