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GMC Owner
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1,114 Posts
Discussion Starter · #1 ·
So last night I am driving down a back road and have my brights on and all is good. Then I pass a car, shut off my brights and pull up to a stop sign. I roll down my window and notice the lights dim, then roll it up and they dim again, put the signal light on and they dim with the light. So i turn the corner and notice the voltage is jumping from about 13-15, increasing with rpm and then dropping when it shifts. So i play with them windows again and this time the lights inside the cab as well as my headlights flicker. Then I try my brights again and every light in the cab shuts off and the radio resets. So I shut off my brights quickly and everything comes back on. When the interior lights were off I got a couple lights on the dash but I shut the brights off so fast I couldn't tell what they were. Other than that no check engine lights or battery light came on. So I turn around to head back home and I noticed the voltage is constant at 14 again. So I play with the windows and the brights and everything works fine. All this happened in one driving cycle. I didn't stop or shut it off at all.

Then all day today everything is working fine. Then tonight I got out and start it and pull up to a stop sign. Again I notice the lights dim when I put my signal on. I look at th voltage and it is moving again. Only this time going as low as about 9 volts at times when I was stopping or slowing down. So I drive to my girlfriends and park it before I start playing. I try the brights and the truck dies. So I get out and try to lock it. The lights flash, but no honk. So I check and the doors didn't actually lock. So I lock them with the power lock switch on the door panel and all is fine. I walk away and about 20 seconds later the horn honks 3 times from when I tried to lock it before. So I try locking it again and the horn honks and the doors lock again like nothing was happening.

I don't know what is happening. It sounds to me like an alternator or voltage regulator. The only think that may have messed it up is that I washed the motor earlier in the week. Only with a garden hose, not a pressure washer and I even covered up the alternator with a bag.

Another question I have is whether I can put the bigger alternator on. I believe that these come with a 105 and 145 amp alternator. I think mine has the 105 amp now, but I am planning on putting e-fans on and stuff so it would be nice to have the bigger alternator.
 

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HOT AIR BALLOON OWNER
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14,932 Posts
I'm not going to read all that.

Put a volt meter on the lug and see if you have power... then trace it to the Red Power Box... then to the battery. If so, then get it load tested... ONCE YOU VERIFY THE GROUNDS.

If still acting up, scoop up a 145A. It fits fine, just need longer belt... and if you're doing one belt, replace the A/C belt while in there.
 

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481 Posts
make sure all your cables are tight and clean (no corrosion etc) if all is good, have the battery and alternator tested.
 

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GMC Owner
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1,114 Posts
Discussion Starter · #5 ·
So I tested the alternator and battery at my dads store today. The alternator didn't clearly fail the test but it did seem like it might be giving a little bit of fairwell warning. So I threw a 145amp on it and it seems to be fine. Oh and I left the ac belt b/c I replaced them both a month ago. I did of course replace the serp belt with the longer one.
 
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