Had a bit of an emergency, Electrical mystery disaster of sorts.

[juanprado]

Circuit Breaker

I ripped off a pic from epay just to make sure you were looking for the right critter. If I remember correctly, there are only 2 of these bolted high to the firewall almost to the hood line close to where the speedo cable and other air hoses go into the dash.

I think all M939 flavors are the same. I could always take a pic of mine tomorrow?

 

[juanprado]

I just had a quick look on my M931A1 and couldn't find them? Do they move around with different versions? And what do they look like? Are they buried in harnesses? I'm looking for the one for my horn circuit in particular.

I don't recall which circuits they protect but I know the horn ground wire by the air horns under the hood has a diode in it by the heater.

 

[The HUlk]

Thanks for the info guys, I'll have another look and report back. I have a no +24v at the horn problem so I figure the fuse is suspect.

 

[The HUlk]

I found em right where juanprado said thay'd be. The one toward the passenger side next to my shiny new air governor is open circuit. I'm fairly certain this is the one for the horn and is the reason it doesn't activate...

 

[Swamp Donkey]

I just had a quick look on my M931A1 and couldn't find them? Do they move around with different versions? And what do they look like? Are they buried in harnesses? I'm looking for the one for my horn circuit in particular.

I don't know if they moved on the different versions either but mine has four, although I think there is a 5th one. Using the pictures posted of the circuit breakers, I'll let you play Where's Waldo, lol.

There are two above the treadle valve, mounted on support bracing. One above the yellow air line and the other is above the blue wire. Top of treadle valve is in the bottom of the picture.



There are two more mounted on the engine side of the firewall, above the engine on either side. One of these might go to the horn circuit.



I think Juanprado is correct that there is one behind the gauge panel too. I'll be pulling the gauge panel tomorrow night to replace the air pressure gauges. I'll check while I'm back there.

 

[The HUlk]

I don't know if they moved on the different versions either but mine has four, although I think there is a 5th one. Using the pictures posted of the circuit breakers, I'll let you play Where's Waldo, lol.

There are two above the treadle valve, mounted on support bracing. One above the yellow air line and the other is above the blue wire. Top of treadle valve is in the bottom of the picture.

View attachment 608472

There are two more mounted on the engine side of the firewall, above the engine on either side. One of these might go to the horn circuit.

View attachment 608473

I think Juanprado is correct that there is one behind the gauge panel too. I'll be pulling the gauge panel tomorrow night to replace the air pressure gauges. I'll check while I'm back there.

Thanks for posting, they are easier to find for me then waldo. This should help rivercreek get to the bottom of his no gage, no blower problem.

 

[Swamp Donkey]

The gauge panel troubleshooting work package is in the -23-1 TM and begins on actual TM page 104-1. The circuit breaker to the right of the treadle valve is for the gauge lights.

 

[rivercreek]

You all are absolutally right about spare parts. Ive got 2 whole shelves full of them and a parts truck (Mostly used up now. Need another parts truck) and I still seem to need all the stuff I aint got. Ive learned a lot over the last few years about what fails regularly, but there's always more to learn and there is no such thing as too many spare parts, thats for sure. I actually did have a spare PCB box until the blizzard - had one take a dump on me then (no start condition) so yep, more spares will be on order.. I need to spend some time learning how to diagnose and repair them as well though. Solenoids are simple, but i'm not sure the purpose of all those diodes everywhere. And I still don't know what those two green wires do either. Got some homework to do. We're still out in this mess now, and the truck has done perfectly so far with the wire bypass. Thanks again !

 

[The HUlk]

but i'm not sure the purpose of all those diodes everywhere. And I still don't know what those two green wires do either.

The purpose of the solenoid diodes is to dissipate stored energy in the solenoid coil when it is deactivated so a voltage spike doesnt occur. It's a circuit protection thing.

Where do the other ends of the green wires go?

 

[sal01]

I have a 923a2 have some of the same problem with the gages sometimes work sometime no work, thanks for the info still looking for some manuals. Plus will the muffler from a M930 fit a M923A2.

 

[The HUlk]

still looking for some manuals. Plus will the muffler from a M930 fit a M923A2.

Yes the muffler will fit, it's a common part on all of the M939 models.

Manuals are here...

http://www.steelsoldiers.com/showthread.php?121487-TMs-for-M939-Series-Trucks