Thread: Wiring a Military Surplus Hummer

Has anyone ever wired a Military Surplus Hummer with emergency equipment? I had a department call me today and said they just bought one of the military surplus Hummer's and want me to outfit it with a lightbar, siren, and mobile radio. Should be fairly easy, but I do know they are 24 volt systems. My other question is, which battery is used to hook the emergency equipment power to?

We had to help my buddies with that also. We advised to tap in between the two batteries and ran it though fire wall. But we where wireing up CBs for my buddies combat unit. We sent a bunch of CBs to them and they asked how to wire them in. that is what they did and worked great.

Deleted due to accidental double post.

They are 24 volt, we installed go lights, sirens, power inverters and other stuff over seas. Granted some equipment was 24 volt equipment that we installed. But what we did was created a buss bar in the battery box off of one of the batteries for 12 volt only and 24 volt. Worked very well for us. If I can find my pictures of this set up I will post them up on here. I worked in the communications section and we installed all kinds of stuff on the Hummers in our unit over there.

The current military M998 Hummer (and the previous ones, as far as I know) are 12/24 volt systems and already have a 12 volt bus as standard.

I was working on the "new" uparmored 1151s which did not have the buss bars in them and we added them this was 06-07.

I believe the battery with the ground going to the frame is going to be your 12 volt batter. On my departments Chevy CUCV, we ran a large hot wire from this battery to a junction and fuse block.

Originally Posted by CenTexPSE

I believe the battery with the ground going to the frame is going to be your 12 volt batter. On my departments Chevy CUCV, we ran a large hot wire from this battery to a junction and fuse block.

I have never worked on a M998, but I own 3X CUCV trucks still original 24v. The front battery as stated above with the ground is 12v and what you hook up to for 12v appliances. You can also connect to the front of the second battery that is coming from the fist battery, that is also 12v. Keep in mind that this is the CUCV setup, not the M998 pictured below.

I thought the military had to destroy the Hummvees at the end of their use as part of the contract between the gov't and AM General. Or can local gov't still purchase them?

You can purchase an older model humvee from a few places. They are readily available as well as parts availability. I do believe that gov't agencies such as police, fire, and ems can purchase the newer retired models as long as they agree not to sell the vehicle to the public at the end of its use with the organization.

Never, ever take the route of getting 12vdc from a 24vdc system simply by tapping only one battery. It will create an un-level battery system with one battery reading lower than the other, thereby failing the batteries by over boiling the battery with the higher voltage and the low battery will always be undercharged. Contrary to what people thing, voltage doesn't travel and "even out" between the two batteries like one would expect with two fuel tanks. The only fix for this is to add a 12vdc alternator with a dedicated 12vdc battery or install a 24vdc to 12vdc converter.

Tapping such a system will result into headaches down the road. Not might, will.

For further reading, I've found this...

12-volt and 24-volt systems

I did some more reading, and this is what I found:

"Your transmission (4L80e) is already 12 volts. The HMMWV A2 has a dual output alternator that charges both 12 and 24 volt circuits. Your transmission taps off one battery and sends 12 volts to a bi-voltage relay next to the brake switch. When keyed on-the 24 volt relay then powers all 12 volt circuits. The transmission computer is fed through the two vehicle speed sensors (VSS) that are mounted on the transmission case, and sees input from these two sensors, a 12 volt powered brake switch, and throttle position sensor." (12v 24v dilema [Archive] - Pirate4x4.Com Bulletin Board)

"The REDARC series of Charge Equalisers (CE) are designed to operate 12V equipment from a 24V system, without the need to buy another 12V battery. The CE Charge Equaliser allows you to 'tap' into the 12V from the lower battery of your 24V system without flattening the lower battery or overcharging the upper battery. REDARC charge equalisers are available in 3, 10, 20, 30, 40 and 60 Amp models. The CE Charge Equaliser is a relatively inexpensive, simple way of getting pure DC battery voltage to run 12V equipment from a 24V system." (CE Series Charge Equaliser | Redarc Electronics)

"A major decision for those converting a military vehicle to a fire truck concerns the electrical system. The military vehicle will be 24 volt and most fire appliances require 12 volt. The HMMWV’s are no exception. Project 56C guides you by showing how to add a separate 12 volt electric system, keeping the 24 volt one for the vehicle and using the 12 volt for add-ons. Appendix A provides a schematic for wiring the system. (http://www.roscommonequipmentcenter....cts/rec56c.pdf)

or heres an idea... How about using 24v equipment? nearly everything thats available in 12v is available in 24v

Originally Posted by iCrash

I thought the military had to destroy the Hummvees at the end of their use as part of the contract between the gov't and AM General. Or can local gov't still purchase them?

I just acquired a HMMWV for my police department from the DoD through their 1033 program (for free). The DoD maintains title to the vehicle and because it is a tactical vehicle that may not be FMVSS compliant, it MUST be returned to the DoD when finished. Has nothing to do with an AM General contract. Fire Departments getting HMMWVs from the Agriculture Department have the same restriction. From what the DRMO folks tell me, the same thing happened when Jeeps were replaced with HMMWVs. I just saw two Jeeps in a DRMO somewhere in the South, and they can't be sold to the public for the same reason.

Originally Posted by cory y

or heres an idea... How about using 24v equipment? nearly everything thats available in 12v is available in 24v

Our department doesn't have the cash to buy 24 V equipment for our "new" HMMWV, but we do have a number of old bars that will likely end up on that vehicle.

If you don't want to install a second alternator, you can use a battery equalizer, such as the units from Vanner.

These are used on most big buses and some trucks. Check Fleabay.

Originally Posted by iCrash

I thought the military had to destroy the Hummvees at the end of their use as part of the contract between the gov't and AM General. Or can local gov't still purchase them?

They used to strip 'em bare and rebuild them, due to armor and other crap being so high. They also do this with the M1A1 and M1A2 Abrams tank. Saves a shi* load of money. But you can still get them stripped around here (no doors, no armor, no engine/tranny, etc.), just the body.

Originally Posted by SoloRTP

If you don't want to install a second alternator, you can use a battery equalizer, such as the units from Vanner.

These are used on most big buses and some trucks. Check Fleabay.

That is the route we chose for our HMMWV. Plenty of room in the battery box to mount it and we got one (new, unissued surplus) free from the DoD.

Literally just google "24v to 12v convertor". It will give you hundred of online stores and plenty of options. We have one installed on an old chevy surplus to run a full Whelen edge and code 3 siren.

I dont really have anything to add but here is a pic of a nearby fire departments HMMWV.

Originally Posted by chfdbigbad

I dont really have anything to add but here is a pic of a nearby fire departments HMMWV.

That is freaking awesome.

Originally Posted by chfdbigbad

I dont really have anything to add but here is a pic of a nearby fire departments HMMWV.

That's a HUMMER (looks like a 93 ish) so it's 12volts

Humvees run on 24 volts.

I have a 99 H1.

What our dept did with a military 2 and 1/2 ton truck, aka duce and a half, is add a 12v system to it. All of the original stuff that was on the vehicle stayed 24v and we attached a 12v 200 amp alt to the engine, connected it to a 12v battery and ran all of the lights and radios on that ckt.