Don't know how long my alternator has been holding on because it always has registered what would look like the proper 13.8 Volts on the dash but usually my Klein voltmeter would measure 15.9V while charging and I don't know if that is severely outside normal, or fine.

Recently within the last month or two I've noticed slight light pulsing and I kicked the can down the road now to where it may look like I'm some sort of half *** emergency vehicle. Looking at $150 ish for a Bosch or Denso or about $80 for a tested used one shipped to see if that is actually the problem.

I've Upgraded the grounds on the Alternator with #4 wire with a #4 wire link from that same point by alternator going over to a ground stud that I installed in the body by the battery. I don't know if there is some sort of regulator or rectifier I can install to remedy things or if I'll need to swap alternators or have mine rebuilt locally. Haven't priced rebuilding it.

 

This is a fairly common problem on these old trucks. It's caused by the voltage drop in the circuit from the ignition switch to the voltage regulator. To solve it many people add a relay to the circuit such that the power to the VR and the alternator field comes through the relay directly from the battery. I used #10 wire for this. The power from the ignition switch now just energizes the relay so the battery won't drain while the engine is off.

Edwin

 

Is the meter pulsing or the lights?
My lights pulsated (not the meter) and I tried EVERYTHING. Finally discovered a wire that had been probed and was corroding from the inside out...

 

My truck does this, if I hit the turn signal all the gauges move a bit. I check all the grounds... maybe I have a bad wire as well.

 

Thanks for asking, I meant to include that info. The meter does pulse now. It started when the lights started pulsing not too long ago. It used to read right at 13.8V-14V all the time while engine running.

 

I can't remember how much the meter needle pulsed but it did, which led me to replace the alternator even though it tested ok (and was). But the lights were still bad, like an emergency vehicle...

I cleaned grounds, added new grounds, installed exterior voltage regulator, nothing helped. I gave up and just decided to become a constable or something so my lights would make sense...

One day I was under the hood and on the driver's side fender notice a wire with a spot of bloom on it. Digging in to it, it was rotting in that spot from the inside out. I replaced that section and everything was wonderful again.

 

Last January, I replaced the crowsfoot electrical connection with a common positive post with lugs soldered to the fuse links and screwed to the common positive terminal. that was 22 months ago and some of the screws were loose. I tightened about5 or 6 screws. Well the dash voltmeter is reading 13 again, the lights are not pulsing whatsoever and I can concentrate on injector stuff again.

That crows foot replacement was somewhat of a last minute scramble to get my truck back on the road last year. Hey, a wooden cigar box and a bunch of cheap terminals from del city lasted almost two years with no maintenance! can't complain. Thanks to those that suggested weak ignition circuit. That's basically what it was but with an extra handicap.

Truck accelerates with a little more confidence. My electric pump was powered from that post too.

 

You need to trace the wiring from the battery through the auto shutdown relay to the alternator. Someplace in there is your voltage drop. The 92 93 model years were taken off the ignition switch and put on a relay to solve the problem 89 to 91 with the external regulator had. However created new problems in the process like overcharging which is easily corrected.

 

I think i found the voltage drop in the loose terminal screws. were you talking about something further?

 

Run a separate ground from the VR housing to the firewall.

Assuming you have good battery to frame/body grounds.

 

Glad you figured it out. Electrical probs can be really frustrating.