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M1083a1P2 No cab power

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polk738

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JBLM, WA
Hey guys, I have an M1083a1P2 here at the shop I am inspecting, doesn't seem to be any cab power at all when I hit the green battery switch, I have gone through the troubleshooting in our IADS system, and this is what I've determined so far
-Batteries are good at 24.6 V
-Main battery disconnect switch is okay
-24V/12V relays are okay and have power next to the MBDS
-LBCD has 24V and is okay
-power is getting to the main terminal lug behind the PDP
-the one place it is not getting power that it should is PX36-1 that goes to the K1 relay behind the PDP
-Troubleshooting determines there is an open in the wire that goes to the connector behind the instrument panel, I believe its connector 29 pin H but I did a continuity check between PX36-1 and pin H and there is continuity, not sure where to go from here, anyone have any insight?
 
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Ronmar

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I don't have that exact diagram in front of me right now but if I recall one side of relay K1 and K2 coils is connected to ground. the ign switch power for both inside and outside ignition switches originates at CB45 in the power panel, and is delivered to the inside remote battery disconnect switch in front of your knee when in the drivers seat.

From the remote disconnect it feeds to both inside and outside ign switches, and on to the k1/k2 relay coils... are all the inside and outside disconnect and ign switches lined up properly and all their wiring in order? If CB45 is ok, what happens when you switch on the outside ign switch in the passenger front wheel well?

If you have 12 and 24 battery power to the battery terminals X1 and X2 and inputs of K1 and k2 that is still there when the ign sw is turned on, I would follow the relay source power from CB45 thru the associated switches(inside batt disconnect, inside/outside ign sw, to K1/K2 relays) and see why it is not making it to K1 and k2 with ign switch turn on...

Remember voltage is not good until it tests good under load...

I can access the proper drawing later this evening....

Good luck
 
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polk738

Member
32
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Location
JBLM, WA
Ronmar said:
I don't have that exact diagram in front of me right now but if I recall one side of relay K1 and K2 coils is connected to ground. the ign switch power for both inside and outside ignition switches originates at CB45 in the power panel, and is delivered to the inside remote battery disconnect switch in front of your knee when in the drivers seat.

From the remote disconnect it feeds to both inside and outside ign switches, and on to the k1/k2 relay coils... are all the inside and outside disconnect and ign switches lined up properly and all their wiring in order? If CB45 is ok, what happens when you switch on the outside ign switch in the passenger front wheel well?

If you have 12 and 24 battery power to the battery terminals X1 and X2 and inputs of K1 and k2 that is still there when the ign sw is turned on, I would follow the relay source power from CB45 thru the associated switches(inside batt disconnect, inside/outside ign sw, to K1/K2 relays) and see why it is not making it to K1 and k2 with ign switch turn on...

Remember voltage is not good until it tests good under load...

I can access the proper drawing later this evening....

Good luck
Click to expand...


Hey Ronmar thanks for the reply, I do apologize that I went through this kind of fast so there a few details I left out that I'll try and go through from memory.

-the K1 relay behind the PDP has 2 TL's and a connector the first one is ground which is good I tested it, the second one should be TL512 I believe which is good and has 24V, the third is PX36, it's a 2 wire plastic connector labeled 1 and 2, 2 is 3041A which goes to ground 1 is 1548 and goes to the cab ignition switch, this is the wire that should have 24V but does not for some reason. The remote switches on the passenger side wheel well had no effect, MBDS, relays and shunts next to the batteries all tested out okay. CB45 is okay
 
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Ronmar

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OK, 3041A and B are the k1 and k2 coil ground wires. 1548 is the 24V ignition switch power in from both IGN switches to the coils of k1 and k2. If neither ign switch works and CB45 is passing power, I would look to the inside remote disconnect switch under the drivers dash or somewhere along the path from CB45, to drivers dash disconnect, and on to ign switches...

I think the inside batt disconnect switch connector is PX-51. wire 1586 to Pin 1 on the inside disconnect sw connector should be power in from CB45, PX51 pin 2 should be 24V out via wire 1001 and 1004 to the two ignition switches...
 
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polk738

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JBLM, WA
Ronmar said:
OK, 3041A and B are the k1 and k2 coil ground wires. 1548 is the 24V ignition switch power in from both IGN switches to the coils of k1 and k2. If neither ign switch works and CB45 is passing power, I would look to the inside remote disconnect switch under the drivers dash or somewhere along the path from CB45, to drivers dash disconnect, and on to ign switches...

I think the inside batt disconnect switch connector is PX-51. wire 1586 to Pin 1 on the inside disconnect sw connector should be power in from CB45, PX51 pin 2 should be 24V out via wire 1001 and 1004 to the two ignition switches...
Click to expand...

Ronmar, Yes you are correct and it should be PX-17-5 that goes to the green batt switch in the dash I am starting to lean towards the remote disconnect switch under the dash being the issue, however when I pulled the panel all the connections are covered in some kind of black substance with no wire labeling, so I am going to have to scrape all that off before I even test for power, which I don't have time for, we are shutting down for the federal holiday weekend so it'll have to be sometime next week before I get into it again. Do you happen to know which connections on that switch are PX 51-1/PX 51-2? Thanks again for your help
 
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Ronmar

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polk738 said:
Ronmar, Yes you are correct and it should be PX-17-5 that goes to the green batt switch in the dash I am starting to lean towards the remote disconnect switch under the dash being the issue, however when I pulled the panel all the connections are covered in some kind of black substance with no wire labeling, so I am going to have to scrape all that off before I even test for power, which I don't have time for, we are shutting down for the federal holiday weekend so it'll have to be sometime next week before I get into it again. Do you happen to know which connections on that switch are PX 51-1/PX 51-2? Thanks again for your help
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no not specifically. There should be a diagram in your documentation somewhere to ID which pin is which for a particular switch connector. I typically confirm the pins using wire numbers to be sure of what I am looking for..

if you can pull the connector it should have 4 or perhaps 5 wires connected to it(2 wires on one pin). Only one of the 4 switch pins used should have 24v from CB45... If you have one pin with 2 wires landed on it, I suspect that would be the output to the two ign switches where the 24v gets sent or they spliced them together somewhere further along the harness...
 
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Ronmar

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I think JBLM is where my 1079A0 finished its service as I picked it up from Auction up in Lakewood off bridgeport way... Had the word "shops" stencilled on the front so I suspect it was a pool vehicle used as a big rolling tool box...
 
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polk738

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JBLM, WA
Ronmar said:
no not specifically. There should be a diagram in your documentation somewhere to ID which pin is which for a particular switch connector. I typically confirm the pins using wire numbers to be sure of what I am looking for..

if you can pull the connector it should have 4 or perhaps 5 wires connected to it(2 wires on one pin). Only one of the 4 switch pins used should have 24v from CB45... If you have one pin with 2 wires landed on it, I suspect that would be the output to the two ign switches where the 24v gets sent or they spliced them together somewhere further along the harness...
Click to expand...
Hey Ronmar hope you had a good weekend, thanks for this info, I believe I can do continuity checks to CB45 to confirm the wire and I'll look for the dual wire in the switch, its all covered in black so theres no labeling or pin ID so I'll have to use a process of elimination. Thanks again!!
 
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polk738

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Well I figured it out, and I feel really dumb, turns out CB45 was bad even though I had probably tested it 3 separate times with my meter, I knew something just wasn't making sense to me when I double checked if I had continuity from CB45 to PX17-5 at the ignition switch, and I saw that CB45 had 25V, I ended up switching out another 15A breaker in its place and it was able to start, I should've just tried this from the beginning, lesson learned I suppose-the thing is, this isn't even the original fault (it supposedly has a very low power output issue) so I hope I can at least get it moved into my bay to look into it more. Thank you Ronmar for you help in the matter, I may need more if it comes to it lol.
 
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Ronmar

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Not the first time I have heard that... the CB's seem a little janky anyway. i kept a few for troubleshooting as they are kinda handy when searching out an intermittent short, but replaced everything in the panel with standard auto blade fuses. Too bad you can't do that:( Glad you figured it out!
 
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GeneralDisorder

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Ronmar said:
Not the first time I have heard that... the CB's seem a little janky anyway. i kept a few for troubleshooting as they are kinda handy when searching out an intermittent short, but replaced everything in the panel with standard auto blade fuses. Too bad you can't do that:( Glad you figured it out!
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The newer Bussmann CB's are totally redesigned and they use the "mini" (ATM) blade fuse interface. Sadly this makes them incompatible with the older trucks but maybe Bussmann makes a similar variant for the normal sized blade fuses.

That all being said - I have not experienced or heard any reports of any of these newer style having a significant (or any) failure rate. Regardless I carry spares of course - you can buy them from Mouser. My truck is going on 30k miles and has all it's original CB's from 2008 and none have failed despite living outdoors in Kuwait and El-Paso it's whole life. I'm thinking they fixed whatever the primary design issues were with the earlier designs.

*Edit*

Here are the new style replacements for the ATC blade style:

 
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