M939 5-Ton reverse light switch

I have found an inexpensive substitute for the Allison reverse pressure switch (which Allison charges 135 dollars for). The part is 416372C1. It is used as a reverse switch in International trucks and I believe on HETs and other larger military tractors. It has 2 terminals on the back, you can solder a pair of female packard connectors without the shell they snap right on and the one I did I filled with rtv silicone and then wire loomed it. I installed it today and it works just like the Allison switch. I ran the wire up into the battery box and I have a relay set up so in reverse the switch closes and gives the relay coil a ground to close the circut and activate the reverse lights. The switch will only activate when reversing with the engine running it works on transmission fluid pressure. There is a bolt on the passenger side of the trans you remove and the switch screws in.

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I am not selling them I am showing that they work in the m939 trucks

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I bought them on the bay 15 bucks each shipped and I had the packard connectors. The ones at eriks seem reasonably priced and he has the correct connector which would make it a little easier.

Check epaY as I found an oe allison for $12. There are many different allison switches with different connectors as the OE chassis dictates what pigtail connector they want/get. They all work the same off the same pressure.

I posted pictures of the the switch and the transmission on my build for "Major Zippidy"

Could you provide a play by play of the wiring set up, I want to hook up a back up light in my M923A2 but am very new to the 5 ton world. How does the switch know when it is in reverse and not in drive ?
Thank you very much

The 1/8 pipe thread port on the right side of the transmission close to the id tag is where the switch goes. The switch senses oil pressure when the transmission is placed in reverse. I am guessing the location is somewhere in the valve body reverse actuation but I am not an internal transmission guy.

Run a constant hot wire to one side of switch. A good place to tap off is the circuit breakers on the firewall by the pcb box. Run a wire from the other side of the switch to the back of the truck for your lights and alarm. The switch is always open so there is no contact and the lights/alarm are not on. When the pressure switch gets oil, it closes completing the circuit and the lights and alarm will work. Ground the lights and alarm where you mount them.

Really not much too it.

This way they are wired to come on as long as the transmission is in reverse like trucks/buses are set up. It is also a reminder to shift back to neutral and not leave it in gear/reverse. No toggle switch etc

Thank you very much, exactly what I was needing. Hope to make it to one of the events soon and meet a few of the fellow 5 toners...

Use a 24v relay in the batt box. Ground one side of the switch and run the other to the relay coil and the other side of the coil to a fused positive. Via the relay you can switch 24v or tap off the center of one batt pair for 12v depending on what light you use. I prefer multi volt led lights. Always fuse everything.

as always the is a cheap fix to an expensive problem

Great advice, this site and people is awesome, thanks for the info.

Added wiring and switch for back up lights today on my M923. Used international part # 416372C1 as Suprman suggested.

(See picture) Switch port location is just forward of the trans data plate approx. 2 inches, level in height with the tag(passenger side of trans).

Required a 7/16" wrench to get the pipe plug out. Use Teflon tape or thread sealant on the switch threads before installing, and have a rag ready catch some oil when the pipe plug is removed.

Helpful info, thanks.

I'd wire the relay power to an ignition switched source, for 2 reasons:

1. In case the switch or relay ever stick on, the reverse lights/alarm won't be stuck on with the vehicle off. Rare scenario, but anything can happen.
2. Some people leave their shifter in a gear besides neutral as part of their anti-theft, to disable the starter.
-addtionnal:
3. I'd put a manual switch on the reverse alarm part, in case backing up late at night in a subdivision (me).
4. Also manual over-ride switch to feed the relay so the reverse lights can be actuated as rear work lights.

Or just put a toggle switch on the dash.

Thank you for the info in this thread. I was able to get the reverse lights to work with your knowledge and help. Thanks!

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