M35a2 keeps blowing headlight

[Bobweb]

My driver side headlight keeps blowing. Any suggestions on what the issue could be? I took apart all the connections and checked for bad wires. They all looked ok. cleaned ground to the frame, re-assembled. Stayed bright for one run, next time I turned the service/drive selector on it blew again. I am not
Much of an electrician. Any help would be appreciated. Thanks

 

[ldmack3]

Did you confirm the voltage at the connector was correct and stable?

 

[Bobweb]

No, what should it read?

 

[Barrman]

It reads like a wiring issue for that one side. However, the rubber isolators for the headlight panel are there for a reason. There is also a note in the 1964 TM about making sure the idle speed is high enough for just this reason, blown headlights because they got shaken to death. 850 is stuck in my head.

 

[Bobweb]

Ok, I’ll give it a look and report back

 

[glcaines]

I had a similar problem with one headlight on an M35A2 I used to own. I went through three Chinese manufactured headlight bulbs, all on one side, in about two months. I believe they were leaking air because when they failed, they flashed and turned black. I then found an NOS Sylvania headlight bulb and never had another problem. The other side already had a U.S. made bulb.

 

[Bobweb]

That almost sounds exactly what happened to me. When I bought mine, driver side was dimmer than passenger side, but would turn on/off consistently, without fail. I went to adjust the beam height and cracked the headlight glass. Purchased a new one/installed and blew immediately. Ordered a new one, installed, drove once and then blew again. The pictures are the third new one I have bought after the original I received with the truck . I want to figure out what’s going on before I install this one cause it’s starting to get expensive!

 

[HDN]

I just looked up that listing. It looks like they're shipping surplus sealed beam headlamps. I'd think they'd be good to work with your truck without issue, so I'm thinking it's either an electrical problem or the idle is set too low like @Barrman mentioned. Your voltage should read around 24 volts at the lamp contacts. The truck, when stock, should be 24 volts everywhere.

 

[Bobweb]

I really appreciate all of you guys. Thanks for the knowledge. In the morning I’ll start checking voltage and report back

 

[fleetmech]

remember, thats 24volts nominal, so you should see a slight variation of 1-2 volts higher if the truck is running/ charging.

 

[GopherHill]

Get a headlight shell/reflector that uses H4 bulbs of the 24 volt variety. They are out there on Amazon and other places. You just make a headlight plug to Packard adapter. They are pretty vibration resistant and MUCH cheaper.

 

[G744]

Don't torque the retaining ring screws past the 'snug' point.

DG

 

[Bobweb]

Don't torque the retaining ring screws past the 'snug' point.

DG

Roger that

 

[Bobweb]

Ok im back. Tested and got 24.86v

picture of the blown headlight

grounds have been cleaned at the frame

wires are rough but no metal showing

any other tests you guys can recommend? I’m looking at the tech manual under trouble
Shooting but not having much luck

 

[WOLF DOG]

That almost sounds exactly what happened to me. When I bought mine, driver side was dimmer than passenger side, but would turn on/off consistently, without fail. I went to adjust the beam height and cracked the headlight glass. Purchased a new one/installed and blew immediately. Ordered a new one, installed, drove once and then blew again. The pictures are the third new one I have bought after the original I received with the truck . I want to figure out what’s going on before I install this one cause it’s starting to get expensive!

I think you got some bad headlamp replacements. Several years ago I recall hearing about a bad batch of lamps being distributed at MV rallys and shows, don't remember the brand. I've experienced the same scenario but mine were both sides. Also I feel that if you were having a voltage surge, it would be blowing out all the lights that were turned on when the surge occured. However with these older trucks being simple 24v systems (no electronics), I don't really see where a voltage surge or spike could come from. A bad ground won't create a spike in voltage.

 

[Bobweb]

I think you got some bad headlamp replacements. Several years ago I recall hearing about a bad batch of lamps being distributed at MV rallys and shows, don't remember the brand. I've experienced the same scenario but mine were both sides. Also I feel that if you were having a voltage surge, it would be blowing out all the lights that were turned on when the surge occured. However with these older trucks being simple 24v systems (no electronics), I don't really see where a voltage surge or spike could come from. A bad ground won't create a spike in voltage.

Well, I think I’m going to hold my breath and plug the new one in. If it blows again, I’ll find a new person to order from or go the direction that gopher hill recommend

 

[WOLF DOG]

Bobweb, after thinking about this a few minutes, I think you could get a higher voltage than safe for your lighting if the voltage regulator is malfunctioning. However as said before, it would effect all operating lights, not just one.

 

[Bobweb]

Bobweb, after thinking about this a few minutes, I think you could get a higher voltage than safe for your lighting if the voltage regulator is malfunctioning. However as said before, it would effect all operating lights, not just one.

When I got the truck, the driver side was always a bit dimmer than the passenger side. Any reason for this other than a failing element in the bulb? Could that be the voltage reg going bad?

 

[WOLF DOG]

When I got the truck, the driver side was always a bit dimmer than the passenger side. Any reason for this other than a failing element in the bulb? Could that be the voltage reg going bad?

I don't so Bob, the voltage regulator controls voltage to all bulbs. They would all be dim if the voltage regulator's output was low and your batteries would go dead

 

[Bobweb]

I don't so Bob, the voltage regulator controls voltage to all bulbs. They would all be dim if the voltage regulator's output was low and your batteries would go dead

I appreciate it thanks, I’ll hook the new lamp up in the morning. Fingers crossed