m939 black box!!?? - Steel Soldiers::Military Vehicles Supersite

powersmoke18 · 01-14-2012, 21:56

so my M931A2 runs great but I'm chasing some electrical ghosts!! when I first got it out of gl it had a minor problem. when I would flip the battery switch nothing would come on so after I moved some wires around and secured connections I got the dash and ignition working. now the problem I'm having is with the CTIS when I flip the ignition switch the control pad lights up for a second and then lights out. so I went to the TMs after reading all about the PCB box I believe that may be where my problem is. apparently the box is not supposed to click when you turn the battery switch on??? As per the TMs is that correct??

steelsoldiers · 01-14-2012, 22:30

The PCB box will click when you flip the switch to the Run position. The PCB boxes are notorious for getting moisture in them, which corrodes the solenoids. Once they get corroded, you will start having intermittent starting problems amongst other things. I had a bunch or poor grounds on both of my 939A2 series trucks. That will cause all sorts of weird stuff. If all off your grounds and connections are good and you still have problems, then start shopping for a new PCB.

powersmoke18 · 01-14-2012, 22:35

thats what i kinda figured. when the gauges wouldnt come on at first i flipped the switch a bunch and it seemed to fix itself. so i'm guessing its that dang box!! just wish there was a sure fire way to figure it out befor i spend 325!!

73m819 · 01-14-2012, 22:49

Has anyone figured a way AROUND the box, remove it all together, look at each system that goes through it and build what is needed, a lot of the interconnection of the systems is to prevent the dumb new driver from doing something stupid like trying to start when the truck is already started, so if the interconnection's are not needed, do away with then.
I run cranes that have the exact same motor (250/290), thay have a on/off switch and a starter button, the on/off (master) energise the main solenoid, this energises the charging system, starting system, and any other system needed, very simple to track down a problem and very simple to fix, I know SIMPLE is NOT MILITARY speak

Bolkbich · 01-15-2012, 07:14

I cut the box on my 817 open and put new solenoids in it

91W350 · 01-15-2012, 08:36

As I understand, it is nothing magical, a resister and a couple of solenoids. I would think connections and grounds would be first to check. One solenoid at least has to be a continuous duty solenoid. I have about 25 800 series boxes in the classifieds, but have been told the 900 is different. Glen

powersmoke18 · 01-15-2012, 20:07

well i did some tm research and figure out what my problems are!! apparently the alternator went south and started putting power to ground!! which fried the ctis ecm, the low air pressure sender, parking brake sender and abs computer! haha. so now i'm on a quest to find these parts!! slowly of course!! but as always the tms saved the day!!!

73m819 · 01-15-2012, 20:14

the 900 box will work on the 800 but the 800 will not work on the 900,

wsucougarx · 01-17-2012, 21:15

Found these boxes on ebay for $130 directly from the CAGE manufacturer

Just search by the NSN and it'll pop up.