Headlight / Blackout switch

[Jack605]

My M37 did not have the original headlight switch and it has been converted to 12volt. How hard will it be to reinstall the original switch and will it handle the increase in current over the original 24 volt system. Most of the wiring in the truck - well to put it simply the wiring is a mess I think someone ripped out the wiring and tried to rewire.

[JStinson]

Are you wanting to mix a 24v switch in with your 12v system? My spidy senses tell me that you shouldn't do this.

Without replacing the entire system, I guess your option is to get a step up converter and rewire the light system to make it 24v. I don't want to discourage you from doing anything you want to do...but this sounds like a nightmarish project to undertake. Not to mention costly (see link). Also, when you're done you'll end up with a mix and match electrical system that only you understand. The next owner will have some serious problems when he or she needs to replace things but doesn't understand the system.

http://www.altestore.com/store/DC-to...nverter/p1058/

To be fair, I might be overstating the problems. Anyone else have an idea about this?

[Jack605]

The problem with using 12 volts on a 24 volt system is the current draw, I can use contactors to make sure the current though the 24 volt switch does not burn them out I was really hoping that the switch could handle the added current (twice what the 24 volt system would draw). I am pretty sure I am re-wiring the front end of the truck, I am having a hard enough time following the wiring due to the current settup and this will allow me to have clean wiring.

[Kaiser2boy]

I may be wrong but as I remember ohms law states that if you put two batterys in parallel the voltage will stay the same but the amperage output will double.

If you put two batterys in series the end voltage will double but the current will be the same as a single battery.

This being true the current in the 24 volt system should be the same as a 12 volt system all thing being equal.

The trick you face is isolating the two systems. Just tapping off the center pole on the battery will give you 12 volts but can lead to feedback and power drain on your system. My truck has a 12 volt heater and I lost hair trying to figure out a way to isolate it when the truck was turned off. I finally came up with a contactor and a heavy diode to stop feedback and battery drain. It works just fine.

[Jack605]

Ohms law is Current equals Voltage divided by resistance. With Resistance being a constant on the truck when you half the voltage 24 down to 12 you double the current, or better said current and voltage is inversly proportional. I am worried about doubling the voltage threw the switch, of course now that I think about it is resistance a constant? Is the resistance of a 24 volt headlight the same for a 12 volt headlight?

[JStinson]

I should have put a disclaimer in my post stating that I know very little about electricity, and actually nearly set fire to my M37 several years ago. Smoke was involved.

[Jack605]

Understand, that is what I am trying to avoid (smoke). My worse electrical mishap was wiring up a motor/generator wrong and blowing a 200 amp fuse, luckily it was only the fuse that was damaged.

[Kaiser2boy]

Its getting fuzzy fast.

Yes if you cut the voltage with the same resistance the amp draw will go up. However if he is switching all his lamps etc to 12 volt stuff it should ballance out. If he is doing some sort of mix all bets are off.
Even if he is mixing lamps the amount of difference in amp draw should not hurt the switch unless there is a direct short and thats what fuses are for. Those switches were built back in the 50s when made in America ment something. Its not like now with everything being made in China and to the barest minumum.
All that said , do one or the other not a mix it will only get messy. As far as I know switching to 12vdc only makes buying lamps cheaper. It adds nothing to the performance of the truck.

[Kaiser2boy]

I should have put a disclaimer in my post stating that I know very little about electricity, and actually nearly set fire to my M37 several years ago. Smoke was involved.

Funny story. When I was in electronics school we had to wire up control panels for motor controls etc.
There was one guy there that was just not getting it. The instructor came over and said to him after looking at his lash up. He said " wow Johnson you have quite a BBF generator here". Johnson asked what a BBF generator was. The instuctor said BBF stands for BLINDING BLUE FLASH GENERATOR. I try to avoid building them.

[n1vsm]

Wiring Options

I was in the same position as you when I first got my M37 - someone did a hack-job trying to convert to 12V. I found it was cheaper & easier to switch back to 24V.
You'll have to see if your starter, generator/regulator or alternator, guages, and distributor are 12 or 24 V. Mine were all still 24V hacked to 12, so the choice was almost a no-brainer.
I replaced all wiring with harnesses from vintagewiringofmaine.com and would do so again in a heartbeat.
I've made a few electrical mods along the way, but the original system is robust when it is in good shape.

[Charles Talbert]

An original 3-lever type switch will function fine in a 12-volt system, we've used many that way. The only issue I wonder about is whether you still have the cannon plug connector in the hacked harness so you can hook it up to a new switch??

Good advice; if the wiring is bad, the ending may be sad. Fix it before you have a sad ending resulting in a burned heap of scrap metal.

[Jack605]

I looked, the connector is missing so I will have to purchase one of those as well. I am hoping to find a connector without the wires I can wire it up my self it is just a matter of leaving enough wire and I want to buy a fuse block and mount it in the truck as well thinking about mounting it in the engine compartment just for ease of access.

[DavidGB]

24volts

Yes, there are more things built for 12 volt systems than 24 and the same item in a 24v version is typically more expensive than its 12v twin, but the 24v system is more efficient. Given two identical circuits, same wire size and length, there will be less line loss in the 24v circuit. Or, you can use smaller gauge wire and save on the cost of the wiring. I lived on board one particular boat for eight years that had 12v and 24v DC systems as well as 120/240 AC. In the boating world as a boat becomes larger/longer it is typical to find DC systems of increasing voltage. This saves considerably on wiring costs. Lengths are not as much of an issue with the shorter runs in a vehicle except where large loads are concerned. If you have any equipment with large power needs the 24v system will handle it either more cheaply or more safely. If you try to run 12v versions of an item on wiring sized for 24v versions you risk creating a fire hazard or premature failure of the item. I am not saying this would happen but that it could happen.
DavidGB

[powerwagontim]

Hi Jack,
I have some take-off canon plugs for the headlight switch. I also have some good take-out switches if you need them. My email is distinctiverestoration@yahoo.com if you are interested in them.
Thanks,
Tim

[Kaiser2boy]

Not to be a spoil-sport about all this huba huba over wire capacity etc but 12 or 24 volts the wiring will be just fine. You are not flying the thing to the moon. Chances are you may never really use all the lighst at all. And if you did what will it be for an hour or so maybe or just to see if they work.
I have a Motorhome built by Gulfstream on a Ford 350 frame with a 460 cu in engine. The wire harness was made in Mexico and it has the thinist crappyest wire you can imagine. It is like 18 guage and it runs from the front all the way 24 feet to the back . It was built in 1997 and I use it a lot . It has many more lights on it than any M37 with all the clearance lights and it has never had a problem, not one with any wire burn out or any other problem . The Dodge wires are not made in Mexico and are not going to melt down due to an amp or two more or less. The head light is the only thing that has any real draw and like I said how many times do you drive your M37 with all the lights on.