Electrical?

Hey everybody maybe someone can help me here, I have a 99 silverado, 5.3l Z71. This morning got in my truck, it started up fine, I then noticed instrument cluster and radio lights were flickering/surging but voltage was at 14v. Put it in reverse and the voltage dopped to about 12/13v like it was about to die gave it gas and it shot back up to normal. So I'm driving and everything electrical goes out and comes back on. Battery flashes, security light flashes, abs brakes come on and off, gauges fluctuate. And noticed it was doing it every 4 seconds. Radio doesnt stay on after i turn the truck off either as it normally does. Doesn't do any of that while sitting idle only while driving and my truck never actually stops running which doesn't make me think alternator is going bad. I know it's hard to diagnose electrical but just looking for a direction to start looking first. Thanks!

P.s. posted last year about a clunk while turning left, change the differential fluid and hasn't done it since! So thanks for that help!

Check Batt cables at both ends for tightness. Check for corrosion. If corrosion is found it's best to replace the cables. The Ign Switch could be an issue also.

The alternators on these trucks have a built in solenoid and voltage regulator. It's most likely the alt. I've had the same issue on my truck, a 2000 Silvy. In fact, many have had the same issue. All that I have seen, the alt is the culprit.

The alternators on these trucks have a built in solenoid and voltage regulator. It's most likely the alt. I've had the same issue on my truck, a 2000 Silvy. In fact, many have had the same issue. All that I have seen, the alt is the culprit.

the alternator does not have a solenoid. this is a typical GM alternator design. voltage regulator is built in as is the norm.

I have dissassembled these many times.

explain what solenoid your refering to and its function .