Electrical questions - Steel Soldiers::Military Vehicles Supersite

chief76433 · 05-27-2006, 20:00

I have never done any electrical work on our 5 ton and have some questions about installing some flood lights on the front.Getting 24v lights is not a problem but I am wondering how to connect them to the truck.Is there a fuse box?Does it just use circuit breakers?I am assuming it is wired pretty much like a 12v car.Right or wrong?I don't want to screw it up so any advice would be appreciated.Thanks.

Recovry4x4 · 05-27-2006, 21:00

It's all negative ground like a car. No fuses except the one in the fuel pump. Cranetruck has set up a relay to draw power from different sources. I'd go that route rahter than draw off a circuit that could possibly overloaded.

Jones · 05-28-2006, 00:00

Here's a listing that's worth it's weight in gold for anyone doing electrical on any M-series vehicle.
www.olive-drab.com/od_mseries_circuits.php3 has a list of all M-series vehicle circuit wires by number (little metal tags near any given terminal end). From that you may be able to locate an unused circuit for spot or flood that you can dedicate to your needs. Like Kenny sez; a relay in the system protects the std. 14ga wiring from overloads in case of heavy amp draw; an excellent idea.

cranetruck · 05-28-2006, 06:19

To connect the flood lights, I would add a separate circuit breaker for the 24 volt feed directly from the batteries. 15, 20 or 30 amp rating depending on your lights.

The reason for my relays is to reduce the burden on existing circuits. I have one relay operated directly by the turn signal flasher, since the new ones are so poorely designed. This way the flasher unit will never be overloaded and I get a full 28 volts on the turn signal lights.
A second relay is used to operate the headlights. The 3-lever light switch operates the relay, which in turn switches the headlights on and off with 28vdc supplied by a separate circuit breaker directly from the batteries.
There is also a relay to operate the selector valve for my heated fuel tank system, but that's a different story.
If you decide to use a relay, remember that a lamp filament has a very high inrush current. A 25 amp mil-spec relay can only safely handle a "lamp load" of about 10 amps.
I use a 25 amp relay for my turn signals and a 50 amp relay for the headlights. Quality mil-spec relays are always available on ebay at a fraction of the original cost.

cranetruck · 05-28-2006, 07:55

Here is the flood light wiring for the M809 series 5-tonners.

cranetruck · 05-28-2006, 08:06

...and the M939 series:

Recovry4x4 · 05-28-2006, 08:27

I, too, have to add a flood light circuit to the old M108. While it had original floods, I'm using the newer M35A2 harness with Packard connectors. It will have the facotry switch at the dash and the switch at each of the 3 floods.