M818 24volt to 12volt trailer lights

[jd-ford-hd]

I searched this forum more than once for the best method to pull civilian trailers with 12 volt lights. Never came up with ideas other than dead-end links, LED bulbs, 24volt relays and voltage convertors. This is what I did to get 12 volts to my trailers. If this setup has been thought of and posted on here before, I apologize to the individual in advance. I have six trailers that will be pulled with my M818 from the fifth wheel. None of them are military trailers. I dont think anyone should utilize this just because I did, I am just showing a simple and inexpensive alternative that works. I used the original trailer slave cable as a sacrificial cable to supply the current the resistor board. A replacement can be easily plugged in if the need to pull a military trailer exists.

This is the resistor used, available at O'reilly's

Aluminum plate used for heat dissipation


Mounted to the rack


Old slave cable visible with new cable attached


For 12v pintle trailers a plug is added to rear fender mount


Check voltage with load applied




14.53 volts is close enough


Ammo can upside down to keep rain out keep air flow


Almost looks like part of the truck painted!






Three circuits plus ground are all that are needed for most trailers. Left turn, Right turn and marker/tail lights. Brake lights and turn signals are the same circuits.

 

[oilcan]

Coulda just swapped the bulbs and built a plug adapter.

 

[tm america]

i like the idea of using the resistors i used relays for my 24 to 12volt trailer set up .how much were the resistors.with the resistor set up you could make it into a cable that plugs right in no need to modify the truck or trailer wiring you could make em with the ammo can with a magnetic mount so it could be attached to the truck or trailer just make the cables long enough to reach either way.i bet there would be a line of guys wanting to buy them.nice job

 

[jd-ford-hd]

Coulda just swapped the bulbs and built a plug adapter.

I own six trailers that are pulled by two Mack trucks most of the time and the M818 occaisionally. Swapping bulbs are for people with one truck and one trailer combos. LED's are too expensive and are a favorite target of thieves.

 

[jd-ford-hd]

i like the idea of using the resistors i used relays for my 24 to 12volt trailer set up .how much were the resistors.with the resistor set up you could make it into a cable that plugs right in no need to modify the truck or trailer wiring you could make em with the ammo can with a magnetic mount so it could be attached to the truck or trailer just make the cables long enough to reach either way.i bet there would be a line of guys wanting to buy them.nice job

Thanks for the compliment. The resistors were $4.50 each and are permanent!!

 

[nk14zp]

Good looking setup.

 

[tm america]

ya switching bulbs is ok if you only have one trailer you're gonna pull .and if you're only gonna be pulling it with your deuce.but what about when you're gonna use a friends trailer or his truck to pull your trailer you would spend more time switching bulbs that towing .

 

[tm america]

where did you get em from thats cheaper than relays .

 

[jd-ford-hd]

where did you get em from thats cheaper than relays .

O'reilly's is where I found them. Should last a lifetime unlike relays.

 

[tm america]

only thing i didnt like about resistors is most of them dont have a very big capacity do you know the rating on the ones you got

 

[jd-ford-hd]

only thing i didnt like about resistors is most of them dont have a very big capacity do you know the rating on the ones you got

I dont know the rating. This resistor is an automotive item made to do exactly what I did with it. I experimented with different loads to establish the exact number of resistors needed. The trailer marker lights were the heaviest load so required the fewest resistors. Weird, huh? The more load put through a ballast resistor, the greater the resistance value becomes. Instructions in the box will guide you through determining the number of resistors required. They can be wired in parallel or series to obtain practically any amp load or voltage reduction needed.

 

[4trans]

do your fifth wheel trailers use air brakes and if they do you have it set up that the fifth wheel trailers hook up electrically the same way they do on the macks you use

 

[jd-ford-hd]

do your fifth wheel trailers use air brakes and if they do you have it set up that the fifth wheel trailers hook up electrically the same way they do on the macks you use

Yes all have air brakes. This mod was done to accomplish the same electrical circuits that are used on the macks that I have or any other civi truck for that matter. Thanks.

 

[jwaller]

this is all you need. simply dial up whatever voltage you want and it's all done.

infinetly adjustable between 6 and 32 volts.

 

[4trans]

may i ask where you can find one of those? Thanks to both of you because i was wondering the most efficient method for pulling civi trailers with a military tractor

 

[jwaller]

may i ask where you can find one of those? Thanks to both of you because i was wondering the most efficient method for pulling civi trailers with a military tractor

I havent a clue where you will find another. it's got a nsn on it but this is the only one I've ever seen. even the transportation company doesn't have them.

 

[4trans]

Is the nsn readable and if it is would you mind posting it?

 

[Civilianfarmer10]

I am building a similar setup with 24 volt relays. Everything was purchased from ebay for around $100.00. I bought a small waterproof electrical box but I wish I would have thought of an ammo can. That would have givien it a more authentic look. One difference I am going to try is that I am going to run the brake light circuit from the switched side of the brake pressure switch instead of using the turn signals. This way the civilian trailer brake lights will operate like evey other civilian trailer.

 

[jd-ford-hd]

jwaller you are torturing 4trans!

"This is all you need" "I have no clue where to find one"

 

[Hammer]

Big bucks.
UTC 2412 B USA Trailer Converter