12volt headlights vs 24 volts.

[m376x6]

Ground Legs

Yes, one in each of the ground legs on the headlamps. Normal headlamps have three wires or connectors. One is a ground or common for the low and high beam elements. For other bulbs that may use the body or housing for ground to the frame you would have to use a resistor for each wire. For instance, civilian taillights, you have a parking or drive element and in the same bulb you may have a brakelight element. Of course military housings use bulbs that have individual elements.

 

[jeli]

RE: 12 or 24 volt M37

Theoretically can you run 12V headlights in series on a 24V system?

 

[CGarbee]

Re: RE: 12 or 24 volt M37

Most folks I know who want to run 12v headlights do so because they think that they are less expensive. Considering how infrequently I have burnt out a bulb in 24v systems compared to the ones in my 12v stuff, I don't think that that is true from a life cycle standpoint. Certainly, keeping the truck stock 24v all the way through makes things much easier from a trouble shooting perspective (if needed) down the road...

I really like Hella E-code H4's... I have them in "everything"... Instalation notes including part numbers are located on my site at:
http://www.garbee.net/~cabell/headlights.htm


As far as the question of running a pump for a plow:
I know of one person who fabricated a bracket and added a 12v alternator and battery so that he could have a second electrical system, one for the pump one for the rest (stock).
I know one other person who installed a dual voltage alternator (bunch were on GL auctions last week...) and a third battery to accomplish the same results.
Of course, one could possibly find a replacement 24volt pump/motor and swap out the existing 12v one and run the entire truck on 24volts...

Meanwhile, congrats on having the truck.

 

[m376x6]

Series or Parallel, To Be or Not To Be

No, unfortuneately you can't. you can on single element bulbs but because the headlight has two elements that go to one ground internally there is no way run two wires to one headlight and then run those two separate wires over to the other headlight and series the discreet elements. It does sound good in theory though. You can do that on fan and wiper motors as well as single element bulbs like those we use on the military vehicles. I've done that on occassion as in a pair of backup lights I had on the M376X6, I've since gone to 24 volt lamps and rubber housings.

Regards,
Bryan Sage

 

[m376x6]

Holy Toledo!

Wait a minute. A much more important issue is who is the hood ornament on that truck????????? OOOH MY GOD, and where can I get one?

 

[jeli]

Re: Series or Parallel, To Be or Not To Be

No, unfortuneately you can't. you can on single element bulbs but because the headlight has two elements that go to one ground internally there is no way run two wires to one headlight and then run those two separate wires over to the other headlight and series the discreet elements. It does sound good in theory though. You can do that on fan and wiper motors as well as single element bulbs like those we use on the military vehicles. I've done that on occassion as in a pair of backup lights I had on the M376X6, I've since gone to 24 volt lamps and rubber housings.

Regards,
Bryan Sage

So it will work if you were willing to give up either high or low beams. If you were stranded with two blown headlights and no 24v replacements available it would get you home.

 

[m376x6]

Re: Series or Parallel, To Be or Not To Be

No, unfortuneately you can't. you can on single element bulbs but because the headlight has two elements that go to one ground internally there is no way run two wires to one headlight and then run those two separate wires over to the other headlight and series the discreet elements. It does sound good in theory though. You can do that on fan and wiper motors as well as single element bulbs like those we use on the military vehicles. I've done that on occassion as in a pair of backup lights I had on the M376X6, I've since gone to 24 volt lamps and rubber housings.

Regards,
Bryan Sage

So it will work if you were willing to give up either high or low beams. If you were stranded with two blown headlights and no 24v replacements available it would get you home.

That and some wire and connectors. Disconnect the ground wire from the harness at inside fender well from one of the headlights, connect your wire to the ground wire from this headlight and run it over to the other headlight. Disconnect both the high and low beam wire and connect your jumper wire to the same wire you left connected to on the first headlight. Since this is an emergency hookup using 12 volt headlights, disconnect the other wire on the first headlight also. If you should accidently hit the headlight floor switch you won't burn out the other element in the first headlight. You're very thoughtful to bring this up so folks can see it and maybe benefit from it. I have seen trucks whose regulator went out and they didn't catch it in time and it took almost everything out. Stupid bulbs and gauges don't seem to want to work for long at 32 to 35 volts or more.

Regards,

 

[Bill W]

RE: Re: Series or Parallel, To Be or Not To Be

Yeah yeah yeah Jeli, but what about the hood ornament on your avatar

 

[jeli]

RE: Re: Series or Parallel, To Be or Not To Be

Hot Chick of the day a month or so ago. Funny when I saw that pic I looked right past her...for a moment.

 

[Bill W]

RE: Re: Series or Parallel, To Be or Not To Be

"I looked right past her...for a moment."

Yeah me too
I think its a 135 or a 211...isn't that sad

 

[M-37Bruce]

RE: Re: Series or Parallel, To Be or Not To Be

Tuesday Weld? (typo)

 

[m376x6]

Re: 12 or 24 volt M37's

You would need two 50 watt 4 to 5 ohm resistors to operate your 12 volt headlights on a 24 volt system. I would recommend 75 watt as they will last longer under the load.

One in each ground leg?

Just now caught your question. Yes a resistor in each ground leg of the headlights. Typical headlights have three posts or connectors, one being the dims or low beam, and the second for the high beams or brights. They share the ground or return leg or post internally and go out of the headlight as one connector. This way using either brights or dims they will be dropped to handle a 24 volt system through a 12 volt headlight. Since the two headlight s are independent you will need a resistor in each ground leg.

Regards,

 

[cranetruck]

RE: Re: 12 or 24 volt M37

The voltage drop across a resistor depends on the current thru it, you know, V=I*R, don't think HI and LO beams will give you the same voltage drop.....

 

[m376x6]

Re: RE: Re: 12 or 24 volt M37

The voltage drop across a resistor depends on the current thru it, you know, V=I*R, don't think HI and LO beams will give you the same voltage drop.....

Actually they're close enough that a single resistor will do the job as it has for me many times in the past. You have to remeber typical voltages vary greatly in a vehicle. Headlights as well as many automotive elements that are primarilly resistive are very forgiving and will tolerate variances in both voltage and respectively current. The wattage differences are slight, what actually makes the difference you see in a low and high beam from them is the position of the respective elements. Headlights have distinct patterns that help them achieve their light distribution through reflection off of the back as well as grids molded into the lense. The formula that is refered to here is one of many that are called Ohm's Law. They deal with different ways to determine voltages, currents, power or wattages, and resistance.

Regards,