Burning out headlights, showing 30+ volts

[darkostoj]

Hey guys, after I burned up my second set of headlights I decided to test the voltage at the headlight leads to see what was going on.

I saw the voltage climb to 30v then I shut off there because I figured something was wrong.

I had a glow plug start box go bad, so I have to assume this was probably the cause of that as well.

How do I go about testing this and fixing it? Does the generator need to be rebuilt?

 

[riderdan]

If it's the 60 amp unit, you can adjust the output of the alternator. Check that you can't adjust it down before having it rebuilt.

The first rely here explains https://www.steelsoldiers.com/showthread.php?106966-HMMWV-Question

 

[papakb]

You didn't state which of the alternators you have on your truck but the voltage adjustment for the standard 60 amp alternator is pretty straightforward. CAREFULLY remove the small metal cover on the connection block. The large 8 gauge power wire is battery power and close to it. There's a small hex head plug you need to remove to gain access to the adjusting potentiometer and you'll need a phillips head screwdriver to adjust it. With your meter on the large output terminal adjust the pot for 28 volts with the engine running. The adjustment is backwards from what you'd expect. Counterclockwise rotation RAISES the voltage, clockwise LOWERS it. You shouldn't need more than about a quarter turn if you do you probably have either a bad regulator or worn our brushes.

Replacing the regulator is pretty easy and can be done in the truck. Disconnect the batteries first. Then remove the 6 screws holding the regulator to the rear of the alternator and pull it straight out the back. There's a couple of slip on lugs that get removed and it comes right off. If you want to replace the brush block it's better to remove the alternator to service it. The brush block is held in with 2 screws. All of these parts can be bought from Southern Automotive (https://southernautomotive.com/cata...d/223?osCsid=5de3f6d4003c7389c336013312ca2577). Make sure to blow out the carbon dust from the old brushes before you put everything back together.

 

[infidel got me]

Alt. is junk....

 

[papakb]

Yes, that may be true but a $60 regulator and a set of $5 brushes beats the heck out of a $500 alternator.

 

[infidel got me]

Not a big fan of the military alt. When they full field/overcharge they wipe out a lot of your electronics if not all. I take them off and throw them on the bottom of my bench. I have 3 or 4 of them now. I replace mine with a delco 21 si alt, which can be purchased at almost any reputable parts store. I've tried adjusting the voltage, didn't change a thing, and finding parts are a nightmare. To me it's easier and cheaper to replace the military alt. with a delco. Done 5 thus far and no problems yet....

 

[tennmogger]

What is the condition of the batteries? Older batteries with higher resistance cells do not load an alternator much and can allow the voltage to drift high. The alternator and regulator may be ok.

Measure the voltage across the two batteries. If either measures over about 14.5, and they are not equal, the higher voltage is probably across a bad battery. If you suspect a bad battery (one has high voltage) you can use a known good battery and jumper it across the bad battery (parallel them). Then check the voltage on the system.

An alternator that's putting out too high of voltage is probably being told to put out too high a voltage by the regulator. Last item I'd suspect bad is the alternator itself. It is obviously capable of generating high enough voltage.

 

[Bill W]

Here is a visual for the volt adjustment if its a 60amp