Strobing lights when idle

Jonathan Ellender · October 21, 2016

Hello all!

new to the forums; got a 98 K1500 (Z71) just picked it up and going through creating a shopping list; one thing i notice was the lights can be dash lights or floor lights on the 4x4 shifter seem to strobe in rhythm of the engine.

Also notice the fuel gauge as well as the voltage gauge will tend to bounce too in the same rhythm. Mainly at idle... was going to replace either the voltage regulator or the alternator.

Anyone seen something similar to this any test i can do to be sure which it is or what not?

Thanks!

barry G · October 22, 2016

I went through my 96, just to go modern.

100% LED...except hot headlamps. I like them in maine in the ice and fog.

problems..

plug wires ..especially the short ones in the back.

top of tranny needs to stay clean.. that creates a loop with minerals.

LED has been incredible... I went so far as to go with electronic relay as the whole thing is now LED.

all weirdness stopped.

the analog gauges will bounce at times, that is their design. Accepting a rhythm is indeed wrong however.

The alternators on these do not play games much. They are either broke or working.

Very smart.. I like these models.

there is an update if to go brand new.

look for "ts16949" in the ad.

Jonathan Ellender · October 23, 2016

I found ground strap is half cut through possible grounding issue thinking about replacing the alternator just to be safe; it has a Delphi on it but nothing to tell me what amperage it is; is there a site i can go to like some dodges have where you can put in the VIN and get all the information on the truck ?

I'm not seeing anything on this truck that tells me which option it has; i need to also replace the pullies and such and need to know that information to order the right size anyways lol..

It has the 5.7 L. 350 Vortec

StepsideGMC · November 1, 2016

Open up your glovebox, the RPO codes will tell you what equipment the truck is spec'ed out with. They're the 3 digit codes, tell you everything from your rear end to what trim options it has...will also tell you if you have a heavy duty alternator or not.

Jonathan Ellender · November 1, 2016

I was looking at those codes; the only matching code came up as 100 amp alt. So I went ahead and got a 105 as that's all i could find; 5 amps difference should not hurt and the belt drive set i got was for either 100 or 105 amp alts since it seems only the 140 amp version is different drive pully.

Jonathan Ellender · December 7, 2016

So this is what I found..

1. Bearings in the altenator or one of the brushes was bad made a racket when free spinning by hand.

2. Ground wire from battery to the fire wall was junk; almost all the way broken but was not the problem.

3. Found the hot wire from battery to the terminal on alt was almost broke through actually when i removed the boot to unhook it it broke the rest of the way.

Replaced that along with tensioner that was a gates (Does not look anything like the gates i bought though) was toast; idler pulley and new belt.

that took care of the amp gauge jumping all over the place and also all lights are steady now instead of strobing.

the one thing i have left is when using turn signals there is a drop in amp gauge as the blinker ticks the gauge ticks along with it.. its sitting right about 14ish cant say if its 15 or 16 its reading but its higher than what i see on Fords and Dodges.. but it drops almost to the 14 mark as it blinks.

Ideas? I soon will be putting 2 small amps in the truck so gotta work out what ever is going on.

Alt i replaced was Remy Gold 105 amp alt. as i could not figure out which it was so i figured 100 /105 should be close enough it shouldn't hurt anything.