M-920 questions

[Karl kostman]

Hello Folks I recently purchased a 1980 M920 tractor and if going through the truck getting familiar with it and its complications I find I have a big question the TMs have not been able to answer. The BIG question is the circuit breaker setup? The TM states that you open the panel on the dashboard which I did and saw all the relays and the started motor circuitry etc. it all there BUT wait I seem to be completely missing any and all circuit breaker button and the panel that they all attach to, its NOT THERE at all!!! I am including the following info if anybody can tell me what is going on with this I would sure appreciate it a LOT!
Registration # NPO30Y
Sales order # 10329869/2
Production order # 7071215
NSN # 2320-01-028-4397
Model # M920
Everything in the TMs seems to match this truck perfectly, my brake lights and blinkers do not work so I started checking for the circuit breakers and found that I dont seem to have any or if I do they are sure NOT where the TMs say they are supposed to be?
If you folks could shed a little light on this situation I would be very appreciative!
Thanks much.
Karl

 

[Tow4]

If there are not a bunch of loose unconnected wires in that compartment with the relays, I would say it has been relocated. Does the truck run and have working lights, etc.?

 

[R Racing]

The curcuit beakers are auto rest so there is no buttons to push.

 

[Artisan]

They are an Automatic Reset. If you remove the short it will reset automatically.
I know, I am not a fan of them either but on the battlefield it is one less part
to carry. I wish I was better w/ electricity to even be able ot tell which one tripped!
I guess look for what does not work!

 

[Artisan]

Karl,


Under both headlights there are electrical junction blocks and
you should consider pulling the headlights and looking at everything,
in particular the grounds in there, if things are rusty take stuff apart
and buff to bare steal, apply dielectric grease and reassemble. It
made my headlight sa LOT brighter.


I also pull ALL GROUNDS and buff to steal and greas ethings up.
Very wise it is to do.

 

[Karl kostman]

Hello guys and thanks for the assistance, AUTO RESET Good Grief, everything on the truck works fine except the rear brake lights and signal lights, the tail lights work great and the front blinkers are good. It looks like I will be pulling a wiring schematic and doing some tracing and testing to see what is going on. Brad great idea on the grounds! Tow4 there are NO loose wires anywhere and what the heck was wrong with manually re-settable breakers? Guys if I need to buy any of the relays in the dash are these readily available, and if so where would you go?
KK

 

[R Racing]

I had a few of my brakers bad. So I replaced them all. Also if you have no brake lights check your switch on the firewall it's a air switch. I have seen them go bad. As for turn signals I had 1 with a bad relay in where the brakers are at. Also had 1 where the relay under the drivers side dash near the turn signal go bad.

 

[R Racing]

Napa carries both the relays and brakers.

 

[Tow4]

Karl, my M915A1 was rebuilt and has the manual reset breakers. If I'm not mistaken, the auto reset breakers are in the same panel. I like the idea of resetable breakers so you know there's a problem. The relays look like commercially available items. you can swap them around to check if you think one is bad. Depending on what model 920 you have, I think the only difference between the 915 is an extra breaker and relay or two.

 

[Castle Bravo]

Something to note too is that the M915A1 is a little different electrically from the M915/M916/M920. On my M916, I had a few things that were wired up like the M915A1. I found it useful to look at the M915A1 TM in addition to the M915/M916/M920 TM.

 

[Monkeyboyarmy]

I think Castle Bravo hit it. The 920 has relays just like the 915. The 915A1' s had breakers. And most of the relays are used for the trailering lights to convert to 24 volt.

 

[Tow4]

They both have relays and breakers.

 

[Monkeyboyarmy]

Oh yeah. Had to go back to my pictures. The breakers on the 915 16.....etc are thermal breakers. Anyway, I would check to see if you have power to wire 35a going to the flasher underneath by the steering column. This comes from breaker cb-2. Also check to see if you have power to the wire going to the brake light switch which is wire 25 that comes from cb-1. I had problems with the connectors on the engine side of the firewall. The terminals would heat up and push out of the rubber.

 

[Coffey1]

OK the front blinkers are working but not the back ones.
Have you checked blubs or the connections.
The brake lights could be bulbs or a stop light pressure switch.

 

[LiqTenEXp]

also check for proper grounding to the light itself. My truck had a paint job in RR in 2011 and they didn't mask off the paint for the front side markers on my M923. I had to take them off and sand paper down the paint to expose the bare metal to get a proper ground again.