Headlight

[Cyrus]

Are there anyway to run 12 volt headlights with a 24 volt system? Thanks, Cyrus

[Lifer]

The short answer is "yes." You'd have to wire a voltage reducer into the headlamp circuit in order to do it, but it can be done. My question is: why bother? The 24-volt headlamps are still available and, even though they're a bit pricey, they tend to last way longer than the 12-volt variety.

[gwalker]

actually if you compare specs 24v bulbs are a lower wattage than 12v ones not a whole lot but some ,I dont know why they made them that way.

[mattveeder]

If you do infact get a voltage reducer and run the 12 volt lamps you will have to do the same to all of your bulbs. I must say that in my mind it seems to make sense that if you use one voltage in one place in your truck you should operate on that system for everything.

[M376X6]

Are there anyway to run 12 volt headlights with a 24 volt system? Thanks, Cyrus

Yes, there is. There is some detailed information on just this subject over at Steel Soldiers right now. Both low and high beams in a lamp use a common ground output connector. Determine the wattage of your 12 lamp and use the appropriate ohmage 75 watt resistor in each of the lamps ground leg. You won't need to mess with any other bulb or lamp as they can remain 24 volt and work just fine that way. There are both domestic and import 24 volt headlamps that are both wire terminals such as is in our trucks and also standard three conductor connectors that are identical to a normal cars pigtail. These 24 headlamps that use a standard three conductor connector are much cheaper than the waterproof type wire connectors that are standard military. A few years back I bought a government lot of headlamps that were 24 volt but they turned out to be the three prong connector type used on regular cars. I cut out some of these plastic conectors from some junkyard cars and wired them to fit the waterproof connectors in the headlamp shell. They've worked great for a number of years.

Regards,
Bryan Sage

[M-Thrax]

As mentioned by Bryan you could put a resister on #16 wire, this wire supplies power from the light switch to the dimmer switch ( mounted on the floorboard) which supplies feed to the hi/lo beams. Someone on the SS site also recomended putting the resister on the headlight ground instead of #16 but either would work. I've never had a issue with 24v headlight(s) going bad so I've never opted to try using 12v instead. I have used a "Vol-Ta-Drop" resisters ( J.C. Whitney) that I modified on my deuce trailer light connector so I could pull my car trailer with and never had a (trailer) bulb blow.

Vol-ta-drop http://news.webshots.com/photo/11021764 ... 2824GluidP

Vol-ta-drop modified http://news.webshots.com/photo/11021764 ... 2824rlDhyg

[M376X6]

As mentioned by Bryan you could put a resister on #16 wire, this wire supplies power from the light switch to the dimmer switch ( mounted on the floorboard) which supplies feed to the hi/lo beams. Someone on the SS site also recomended putting the resister on the headlight ground instead of #16 but either would work. I've never had a issue with 24v headlight(s) going bad so I've never opted to try using 12v instead. I have used a "Vol-Ta-Drop" resisters ( J.C. Whitney) that I modified on my deuce trailer light connector so I could pull my car trailer with and never had a (trailer) bulb blow.

Vol-ta-drop http://news.webshots.com/photo/11021764 ... 2824GluidP

Vol-ta-drop modified http://news.webshots.com/photo/11021764 ... 2824rlDhyg

The reason I wasn't mentioning going to the power feed wire from the light control switch to the dimmer switch is that at that point to handle the power you're looking at very low ohmage resisitor and very high wattage rating in the area of 125 to 150 watts to keep the surface temperature down to a non instant fire starting level. Also not to mention they are really large. These large wattage low ohmage resisitors are incredibly expensive while the 75 ohm resistors are very reasonable. There is the option of taking the two resisitors (75 watt nominal 4 ohm) you would put in the ground legs of the lamps and putting them in parallel on this same dimmer switch feed wire. The major drawback to this method or even the single high wattage method MThrax has pointed out is that when one of the lamps should finally burn out due to age or a hard hit, the voltage is increased to the remaining lamp and it almost instantly burns out as well. But, for the few seconds the remaining lamp stays lit, it will be really really bright. Seriously, if you're looking to go the 12 volt lamp in a 24 volt system stay with discreet resisitors(resistors in each ground leg) this will work reliably. But also be aware, where a 24 volt lamp operates at a nominal 50 to 55 watts, when you drop a resistor in series with each 12 volt lamp to run them on 24 volts, you're now using 100 to 110 watts for each headlight. This is double power or amps that is normally drawn through a 24 headlamp system.

Regards,

[M376X6]

I see where somebody mentioned a special wiring harness for converting to a 12 volt system. I don't want to rub somebodies rubarb the wrong way here so I'll try to eplain what the concept is. Most wiring in an M series such as our M37s is what is called 14 AWG or gauge. This wire is rated at around 15 amps for regular ac applications such as houses factories etc. In vehicles pushing 20 amps through a 14 gauge wire is no big deal but best to keep the current at minimum or below 15 amps. The problem is that as you push more current through a wire it begins to drop voltage and actually acts as a load. A load generate heat. Hence when it really conducts too much current, say by way of a short, it melts the insulation off. Most loads or items needing power in a M series are tied to 14 gauge wires that can easilly handle the current flow. Here's where you need to be aware of what is termed a current budget. Two loads, say headlights. Both are 50 watt, one is 12 volt, the other is 24 volt. In order to get the 50 watts per headlamp the 12 volt load must use around 4 amps of current. The 24 volt load only needs around 2 amps. The 14 gauge wiring will handle either 12 or 24 volt headlights because even the 12 volt lights will use only 8 amps. Taillights and the wirng that goes from the tailights to the trailer connector are even safer because generally the current to run brake lights, marker lights etc, is even less than headlights. Where you might run into problems is where the current to run these various loads comes from. Say the wire numbered 10, generally this is a 12 gauge wire, easilly handling 20 amps. But when you begin to total up the added current for a 12 volt system some of the major power supplying wires could get overloaded. Remember, even a taillight at 12 volts will draw twice the current as a 24 volt taillamp. The circuit breakers that protect the wiring in our M37's care only about amps, not what voltage or watts you're using. Be mindful of how you're loading each particular wire and how exactly you're feeding this wire and all the wires that are in common connection with this major source. It may all seem smoke and mirrors but it is actually pretty straight forward. If you have questions or concerns let me know. I'll be happy to help you out, and for a really reasonable hourly fee.

Regards,
Bryan

[M-Thrax]

Bryan
I forgot that was you ( somebody) at the SS site with all the great info and insight on doing this conversion. I did not think about the heat output as my reducers for the trailer connectors were mounted to the back frame.
Regards
Bill W

[M376X6]

Bryan
I forgot that was you ( somebody) at the SS site with all the great info and insight on doing this conversion. I did not think about the heat output as my reducers for the trailer connectors were mounted to the back frame.
Regards
Bill W

Hi Bill, I've used that method on a trailer that was 12 volt bulbs. Made a box that had a military trailer pigtail with a connector for the civilian trailer harness for a fellow who wanted to pull a trailer with his Duece. Worked great. I kept the trailer side marker lights and the two driving taillamps on the same circuit so that if one (read When) did go out the load was distributed among the other lamps so the voltage rise wasn't too great. Fella was very pleased.

Regards,
Bryan

[ELBUFO]

Please don't run me outta town on a rail, butt.... The previous owner of my very green beasty attempted to convert the lights to 12v. A hack job "par excellence". Being the cheap ### I am, I opted to re-wire myself as all of the old rubber insulation was toast.. What he had done is to "center tap" off the first 12 battery and hook up to a civy pull switch, and cut and splice. I am following suit, but doing it properly. (Wire size, fuse blocks etc.) I know that what I have done is heresy, but it gets the M on the road safely and cheaply, and with wiring I can trust. I made sure to wire it in a manner that enables me to go 24V all the way by simply jumping the 12v fuse block input to the 24V. On the down side...The second battery will be over-charged. Since I don't use the lights often, swapping the batterys around every month or so will be necessary. (good time to clean battery box.) It is a strange coincidence that both my M and my cash are the same color....John