1083a1 Electrical gremlins

[LBCDguy]

Alright so how to make this post not a huge drawn out novel.

I Have a 1083a1 WO/W SN# above 100,000

Whenever the operator would jump into the truck and push the master power switch on the dash to turn on the IGN before hitting the push button start....nothing would happen crank no start.... As soon as i turned the master power switch off on the dash, i tried to start it and it fired right up..... so i know that it starts and runs and i have throttle that means i have power to the TCM ECM the ABS module etc... the only issue is once it started i have no gauges but only a few "warning lights on the dash" i cannot use the lamp test button on the dash either.

SOOO.. once it is started and running i turned the master power switch on the dash on just out of curiosity and the gauges would come on and the rest of the dash lights would cycles and the lamp test would work..... so i was like...hmmmm that's interesting. switch ON dash lights and gauges come to life, switch OFF gauges die out but truck stays running. so i turned off the master battery switch in the truck off, truck shut off like it should turned the battery disconnect switch back on with the Master power switch in the on position tried to start the truck and it STILL will just crank no start..... I broke out the wiring diagram and it looks like the dash runs on the 12v circuit which if I'm not mistaken. is from the LBCD to X1 to the K1/K2 relays then to the separate PDM #1-#4 etc. I have power at the relays and the PDM's is there something im missing here? is the a known issue?

thanks

 

[Ronmar]

Well thats weird. With the main sw off there should be NO ign power. No 24V ign means no starter control circuit no neutral start, no alt excite/starter lockout. So I would suspect your K1 24v ign relay is shorted or it has been bypassed? Switch off, should have 0 power on X3…

What is K19 doing? That is the start inhibit relay. In the A0 it is a latching relay with a pushbutton in the PDP so you can apply power, push the start inhibit and you will get a crank no start for testing/maintenance until you shutoff the ign power. On the A1 it appears they kept this relay as a remote shutdown feature. It is normally de-energized and applies 24v ign power to the ECU(run enable) thru the de-energized contacts(30-87A). On the wrecker variant there is a kill switch on the wrecker control that would energize K19 and it is also wired to latch and would keep the engine dead even after you shut off the wrecker kill, until the main switch is cycled to reset K19 to the de-energized position.

But that is also weird as if that remote kill circuit was shorted once you got it running with the main switch off like you described, as soon as you switched it on K19 would energize and remove 24v ign power from the Engine ECU lust like a remote kill.

I would fix The K1 24v ignition power issue first then re-test and see what it is doing after you regain control of the 24V ignition power…

 

[LBCDguy]

Makes sense to me I will Isolate K1 to see if it is shorted.

updates to follow

thank you