Moisture In The Sealed Lamps?

[Tim Powell]

Hey Crew.
I've got a question. On occasion our M37 sits outside on display. Hot or cold and a few times in the rain.
Several times I've noticed condensation in the lights on the inside of the lenses. I was told on a military
vehicle there is always a very small amount of electric current running thru the wiring to keep the
electric system warm and dry?? Came from someone I really trust. Anyway, I've added a master
disconnect switch to my electrical system. Could this be the case of my moisture problem? I'm thinking
about drilling a small hole (1/8") in the bottom of the sealed lights to let the air temp equalize and maybe
eliminate this problem. Could this be why so many old lights are rusted and corroded beyond repair?
I tried this one time on a sealed CB radio antenna base on a Freightliner I drove and it seemed to help.
I do not plan on running the truck underwater so that's not a worry.
A Penny For Your Thoughts!

Flying Eagle Penny.jpg (9.67 KiB) Viewed 3311 times

Thanks In Advance!

[Carter]

I doubt the " keep the wiring warm and dry " story, not in any manuals I have read. As for moisture in the lamps, that is a reasonably common thing, the lamps are sealed against water not humidity however as the interior warms with the bulb illuminated or the hot sun shining on them the air expands but later as the unit cools a vacuum is formed drawing in outside air and the humidity it contains. In 1966 when I was a member of the 574 Ord. Bn. @ Ft. Knox we had several of the Dodges assigned to us and during preventive maintenance time we would have to remove the doors and dry the lamp interior almost every week. I have no idea if drilled holes in the lamp underside would help or not.

[rickf]

Are you talking about the sealed beam headlights? They are in a vacuum so drilling a hole would instantly blow the light. I have never seen moisture in a headlight. As far as the warm and fuzzy thing, you might want to ratchet the trust factor down a bit for that friend. He is probably still chuckling about that one. It would take a LOT of amperage to keep the wires warm so the answer is NO, there is no power running through the electrical system when it is not turned on. A switch is a switch, on is on and off is off. If you are talking about moisture in the gauges the yes, it is quite common and it drys out as they warm up in the sun or heat. I have hear of drilling a hole in them and I guess as long as you do not plan on going under water it will not harm them, the moisture is obviously getting in anyway. Might as well give it a faster way out.

[just me]

You can always throw dessicant bags in the housings to help alleviate the condensation.

[Tim Powell]

Hey Guys!
OK, I know better than to drill a hole in a sealed beam headlight. 42 years of driving a truck, at least give me a little credit.
I'm talking about the marker lights. Parking lights? Blackout lights? Not the headlights.
I do believe the desiccant might help. Gonna' drill my hole in one light and see if it helps. If so then the rest.
"A desiccant is a hygroscopic substance that induces or sustains a state of dryness (desiccation) in its vicinity. Commonly encountered pre-packaged desiccants are solids that adsorb water. Desiccants for specialized purposes may be in forms other than solid, and may work through other principles, such as chemical bonding of water molecules". Sorry, couldn't resist.

I am also going to call my Buddy and get the story about the current running
thru the wiring again and see if I can post his reply. Most of you guys know him.

[just me]

There is no current running through any wiring if the circuit is switched off. If there was, the circuit would be on! (And your battery would be dead in the morning.)

[Tim Powell]

Hey Crew.
Ok, I just called "Vintage Wiring Of Maine" to follow up on my earlier questionable theory. (the dog ate my homework)
Also, Carter (long time no see!) by "doors" you mean what an old truckdriver would call the lens?
All I remember is "somebody" said "ohm" and wiring? My rememberer ain't as good as it used to could.

Military Lamp Assembly

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[just me]

Drilling a small hole in the bottom of the housing usually won't hurt anything. Make sure it is small enough that bugs won't get in and big enough that surface tension won't defeat the purpose. If the hole is in the bottom of the housing, and it is sealed otherwise, fording operations won't allow much ingress of water.

[Carter]

It has been a while Tim, glad to hear from you.

In the drawing the door is numbered 5 and in the second shot the part number is listed

[MSeriesRebuild]

The early style light fixtures have always had this problem, almost every one we open up has serious interior rust going on. All the trucks we build here get either the later style M Series composite lights or some other type lighting for clients who do not care about all the mil spec lighting functions. We have found that the later style military fixtures typically do not have the condensation issue. LED versions are also available now in the mil spec composite housing, this is the very best option if you want to stay with the mil spec lighting. Cuts any maintenance to near 0, and longevity is outstanding. You can pretty much install and forget the LED's as long as it is done correctly and all wiring, switch, etc., is good.

[PoW]

LED's sure are the rage, but I prefer real incandescent lamps.

They 'look' a lot less obnoxious to me.

A little tobacco bag of desiccant crystals in the housing will keep rust in check pretty well.

PoW

[just me]

Amen to that. I despise LED rear lighting in cars. It bothers my eyes. And with no persistence I actually find it harder to see flashers, strobes and brake lights. And as for headlights, they are bright as hell at the lamp and make for an uncomfortable amount of glare for oncoming drivers. They put a lot of light right in front of a vehicle, but don't put anymore usable light down the road. Or if they do by measurement, it gets washed out by the back glare of the hotspot right in front. I saved the little "Do Not Eat" bags from electronics I buy and put them in my lights. (Too much money and too high quantity to buy them from the usual sources)

[MSeriesRebuild]

LED's are actually the best all around lamps, I understand what you are saying and to each his own. I learned a few pointers quickly when we started to use then in our rebuilt trucks, they MUST be installed and aimed correctly in order to compliment the driver and oncoming traffic. I totally get that many of them you experience in night driving do exhibit glare and blind oncoming drivers, I can't use my glasses when driving at night because of it. I fully believe the reason for most of that is caused by all the universal and Chinese "will fit" lighting products that are out there and sold as retrofits. They may not fit a given vehicle as the original design, along with DIY installations done with little or no attention paid to correct aim. All these factors in combination can produce lighting that really isn't too good.

[rickf]

I put the military LED headlights in my M-151 and I love them. It took a little bit to get them adjusted, I would get my GMRS radios out and give one to a friend and we would go out on a dark road, him at one end and me at the other and drive towards each other. If they were blinding him I made adjustments until they were good for oncoming traffic and surprisingly that also made them better for me. It put a lot of the light out front and out the sides with a sharp cutoff line that reaches out pretty damn far ahead, much farther than standard headlights. High beams!!!!! On flat ground you can see reflectors at a mile easily and everything around you is lit up. They may not be original to the period but if I am driving at night these old eyes need all the help they can get and that trumps original any day. I am going to run the old style original tail lights in mine with the gamma goat lenses but when not in a show or parade I will also have a set of LED tail lights mounted for safety so people on cell phones might actually see me.

[MSeriesRebuild]

I put the military LED headlights in my M-151 and I love them. It took a little bit to get them adjusted, I would get my GMRS radios out and give one to a friend and we would go out on a dark road, him at one end and me at the other and drive towards each other. If they were blinding him I made adjustments until they were good for oncoming traffic and surprisingly that also made them better for me. It put a lot of the light out front and out the sides with a sharp cutoff line that reaches out pretty damn far ahead, much farther than standard headlights. High beams!!!!! On flat ground you can see reflectors at a mile easily and everything around you is lit up. They may not be original to the period but if I am driving at night these old eyes need all the help they can get and that trumps original any day. I am going to run the old style original tail lights in mine with the gamma goat lenses but when not in a show or parade I will also have a set of LED tail lights mounted for safety so people on cell phones might actually see me.

You have found the same result we have; when correctly adjusted, they do not blind oncoming motorist and you do have good light a lot farther ahead than with original sealed beam elements. All our clients that have them really like them, of course we have already handled proper adjustment, so they only see the positive benefit. Another improvement is way less current draw, the generator thinks it's on vacation.