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No electrical power except to low side blower motor

Triple C

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Gentlemen I need some help. I recently sold my 925 to a good friend and neighbor as I felt like I wasn't able to keep it up. He has had it about ten days and called to tell me it wouldn't start. The only thing he has done since he got it is put in a new battery I bought him, cleaned it (told him that would be a problem!) and started it four or five times. I went over to see if I could help and we spent a few hours going over the TM's (I printed them out when I bought the truck.) The problem is, there isn't any power to any of the gauges, no lights, no starter. The only thing that will work is the low side of the heater blower. When you turn the switch to the high side, the needles on a couple of the gauges will move then everything stops. We made sure the batteries are fully charged, the connections are good. We pulled the battery switch and tested both the line coming in (459 I think) and checked to make sure there was outgoing voltage through each of the battery switch terminals. We also tested the control box cable per the TM and it tested good too. I am unable to test the control box because I do not have a tester that will do continuity. We did open the control box and there isn't anything obvious. I am stumped, any suggestions?
 

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Alexsha

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100% sure the batteries are wired in right and not shorted somewhere? The low blower is 12v wired direct to 1 battery and would work if the 24v setup isn't wired right.
 

tractors0130

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Energize each solenoid separately when the PCB is disconnected from the truck and use an ohm meter across the main lugs and check continuity. If one of the solenoids are bad it can be replaced if that's the problem.
 

Triple C

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100% sure the batteries are wired in right and not shorted somewhere? The low blower is 12v wired direct to 1 battery and would work if the 24v setup isn't wired right.
I thought about that too. I looked it over and it looked fine and all the fittings are tight. I did wonder if maybe one of the jumper cables was broken inside. I haven't checked that. Plus, it started after he changed the battery at least three or four times without issue. Guess it is worth a try though. Thanks.
 

Triple C

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Energize each solenoid separately when the PCB is disconnected from the truck and use an ohm meter across the main lugs and check continuity. If one of the solenoids are bad it can be replaced if that's the problem.
Thanks for the help here, now just a little more please. When you say energize them should I take all the lines off the solenoid first and can I do it with minimal voltage to test the continuity? I am way out of my expertise here. Btw, where does one get the solenoid if it is bad? Or what does another PCB cost?
 

tractors0130

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Disconnect the 2 small wires on the front of each solenoid and you will need 24v DC to energize the solenoid to pull in the contactor inside. With the ohm meter connected to each main lug on the side of the solenoid it should go full scale indicating continuity. The copper disc inside the solenoid gets bad spots preventing full contact. You can buy 24v solenoids online pretty cheap or buy a PCB for a couple hundred.
 

Triple C

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Disconnect the 2 small wires on the front of each solenoid and you will need 24v DC to energize the solenoid to pull in the contactor inside. With the ohm meter connected to each main lug on the side of the solenoid it should go full scale indicating continuity. The copper disc inside the solenoid gets bad spots preventing full contact. You can buy 24v solenoids online pretty cheap or buy a PCB for a couple hundred.
I guess I should first make sure I have 24 volt at the solenoid first and if I do then check continuity? Thanks a lot for the help.
 

Swamp Donkey

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When my PCB started going bad I had to flip the battery switch on and off several times to get it going. Towards the end, I had to leave the switch on while hitting the top of the box with a ratchet. The gauges will come to life when it makes contact. Even though it would eventually crank it led to other issues. Sometimes the alternator wouldn't charge. This led to the batteries running down, which led to an ABS fault due to low voltage. After replacing the box all the other problems went away.

If I recall, but don't hold me to it, the only thing that worked when mine wouldn't make contact was the low setting on the blower motor. This would be the 12v lead you speak of. Being that it's 12v I think its on a different relay or something inside the box. I got my new box at Southern Automotive (OEM) for $150. It was freshly made a week before I bought it. They do make them in batches though so there might be a lead time if you go through them.

If you're not able to properly test it electrically then try flipping the switch repeatedly or tapping on the box with the switch on. The box might not be the problem but it sounds almost exactly like the symptoms I was having.
 

Triple C

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When my PCB started going bad I had to flip the battery switch on and off several times to get it going. Towards the end, I had to leave the switch on while hitting the top of the box with a ratchet. The gauges will come to life when it makes contact. Even though it would eventually crank it led to other issues. Sometimes the alternator wouldn't charge. This led to the batteries running down, which led to an ABS fault due to low voltage. After replacing the box all the other problems went away.

If I recall, but don't hold me to it, the only thing that worked when mine wouldn't make contact was the low setting on the blower motor. This would be the 12v lead you speak of. Being that it's 12v I think its on a different relay or something inside the box. I got my new box at Southern Automotive (OEM) for $150. It was freshly made a week before I bought it. They do make them in batches though so there might be a lead time if you go through them.

If you're not able to properly test it electrically then try flipping the switch repeatedly or tapping on the box with the switch on. The box might not be the problem but it sounds almost exactly like the symptoms I was having.
Yep, that sounds exactly like what we are experiencing. Thanks, looks like I probably owe him a PCB.
 

Alexsha

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You mentioned that you dont know if youre getting 24v to the PCB. I would check that first before tearing into the PCB. It's possible that a wire has come loose after having a battery replaced. I always like to do troubleshooting 1 step at a time. Check the simple things. Follow the circuits and see exactly where you're losing the voltage.
 

Swamp Donkey

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Accidentally found this while searching for something else in the -10 TM. It confirms what I suspected but never tested. The 12v feed for the low blower setting runs directly through the battery switch and not the PCB, which explains why low still worked when my PCB went bad. The 24v for the high setting has a relay inside the PCB. Again, the problem might not be your PCB but I figured this might be helpful to pass on to you.

Screenshot_2014-12-09-20-55-15.jpg
 

Triple C

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Thanks Swamp Donkey, I am sure you are right. We opened the PCB today and verified that we had voltage to the small red wire on the lower solenoid as well as power to one side (when the master was on.) Tried tapping it but that didn't help. Thought about bridging across to see if the gauges and lights would work but decided against it. I can't get any voltage to anything on the upper solenoid but it has a jumper that goes up to one side from the side of the lower that would energize if it was working so I assume it won't work until the lower one does. The new owner went to napa and ordered both solenoids today at about $70 each. I told him I would cover them since the only time he has driven it was to take it home he only lives two doors down so he drove it a couple hundred yards!
 

Artisan

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Under the passenger seat isn't there a battery wiring schematic Data-Plate?
Isn't there a small wire that is a dedicated 12V wire you need to hook up and
isn't there a ground AND positive small gauge wires that needs
to be connected as well? Not just the big
main wires but 2 smaller wires too?

I suggest your friend did not reconnect the new battery's correctly.

I have been there and seen this and it was a bitch to get
right / being ignorant like I "was?" (debatable I know! HA! )

He needs to read the TM's / SCHEMATICS and find out just what is supposed
to go where, and make it so, not almost right, but exactly like it
is supposed to be wired or EXPECT big issues.

Look for the wiring schematics in the TM's!

It will all of a sudden come to him after you study it, I DO Believe.

For some reason I remember a 59? wire or something in there, a ground and a 12V lead plus the big wires ?

It is confusing, you need to study the wire schematic and take
deep breathes and put it back to OE condition w/o guessing or EXPECT issues!

This is NOT your problem, IMO. I am pretty sure your buddy eff'd up
when he put in the new battery, in-so-much-that he did NOT keep track of
what went where and or a small wire broke or shorted out. The 2 smaller
wires I speak of "can" ground against the cab floor, pull all batteries ot inspect I
and YES, I know it is a LOT of work, (Be sue to rotate batteries and charge
each battery independently when pulled. I bet if he pulls
all batteries he will find the wires he forgot laying between the two rows of batteries.
BUT SOME HOWEVER,

The M939 Series of trucks also have a MAJOR FLAW / HISTORY, that being the main battery wires.
Usually it is the + or - main power wire from batteries to starter, that loose there insulation near
the DS rear of the engine block. It is pretty much impossible to see this
anomaly w/o doing real work. If you can not see 100% of every inch of
those wires, I mean all sides all the way aroud, you are "Assuming" they are ok.
You HAVE to make SURE!!!!!!!!!!!!!!!! It is a BITCH too! Patience....

I could only find this issue by first, being TOLD about it, then,
by disconnecting the wires at the batteries first,
then disconnecting the same wires at the starter and pulling and
moving them back an forth so as to try to see ALL around every wire
110%! So you can see all parts of the wires that
YOU CAN NOT SEE under from under the truck! If you are persistant
and do a GOOD JOB looking you might all of a sudden see where
one of those massive cables has had its insulation
rubbed clean off raw and it is grounding to the block!

BELIEVE IT.

This issue should be a 5TON Sticky.

I fixed mine temporarily buy sliding a heavy piece of dishwasher rubber
drain hose over the battery cables from the starter w/o cutting the hose
longways, but by just sliding it down over
the battery cables covering the bad spots.
BE FOREWARNED!!!


ALSO, ALL 5 TON OWNERS:

You Need to PULL all GROUNDS and clean ALL surfaces to bare metal, I MEAN
ALL SURFACES, and reassemble absolutely CLEAN to BARE Metal with DI-Electric grease and
make SURE you use Internal / Eternal combination STAR washer between the frame and'
the ground wires / straps. I added 2 more ground wires too, from the cab
to the frame, DS rear and from the bed to the frame at the fuel tank ground too.

These trucks take a LOT of work to keep them mission ready.

Yes, I can make mistakes................... see my sig line
 

Triple C

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Thanks Artisan, It is a good reminder! Start from the beginning. I sold him the truck pretty cheaply because 1) it is a desert storm veteran and I wanted it to go to someone that I knew would take care of it and he will. Number 2) while I love to drive them, I don't care so much for the maint. and I'm not getting younger. I DO take seriously the talk of safety on this forum, better for me to sell it than drive it without the proper maintenance. 3) He is a really good guy that has had some tough luck lately and this will definitely help lift him up. I'm not going to keep paying for and doing maint. on a truck I have sold, but he hasn't even got a plate on it yet. I am going to help him through this and then he should be good. I think I will "Supervise" as in watch, him inspect all the cables as you suggest. He is a heavy equipment operator that is used to working on 24 volt so he probably knows more about that part than I do, but you make a good point, these vehicles are almost thirty years old. We will go back to the schematic and verify that, inspect the cables and go from there. Thanks for the reminder.
 
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