Lights Out. Headlights not working in 2003 M1078A1. P912 and J913 unplugged.

[Erik Erickson]

Thanks in advance for any help. You guys have been really helpful.

I have a 2003 M1078A1. I have the more updated light module - not the 3 level variety. I can't see to get the headlights to work. Other lights do come on. I checked the various breakers and that doesn't seem to an obvious issue. I pulled the dash to remedy a different issue and noticed a wiring bundle that is disconnected.

The wiring loom tags are P912 and J913.

I can start the truck and after the air tanks fill up, the alarm goes off, no dash indicator lights at all.

Then if I connect those two together, the alarm comes on and 3 lights:
Van door (this is a trooper carrier, so there is not Box or door)
Dump body up (not a dump body)
ABS (I rear brakes are caged at the moment - would this cause an issue?)

I also see the K12 light come on in the breaker box.

Two Questions:
1. Any ideas on how I can get my headlight operational?
2. Do I need to plug this wire loom back together or was this intended by the OEM for my model?

Thank again!

 

[wheelspinner]

Do NOT plug those together. 912 and 913 when plugged together cause all kinds of bad things.
As far as the lights, you will just have to start with some basic troubleshooting. Does it have power at the relay? At the switch? Etc.

 

[Ronmar]

CB70 feeds the main light switch. The switch uses power from CB70 to power K7 which is the headlight relay. So first question, does the LED for K7 light when you turn on the light switch to service drive? If not, I would look back thru the switch or the CB70 supply. You can measure the switch output at K7 socket 86…

If K7 powers on it uses power from CB78 to feed thru the contacts of relay K8, the high/low beam relay. K8 being on = high beam, otherwise low beam. K8 is controlled by the column switch. From there it feeds on to the lights. You can pull out K7 and jumper the socket pin 30-87, and the headlights should come on to test that part of the circuit.

 

[Erik Erickson]

CB70 feeds the main light switch. The switch uses power from CB70 to power K7 which is the headlight relay. So first question, does the LED for K7 light when you turn on the light switch to service drive? If not, I would look back thru the switch or the CB70 supply. You can measure the switch output at K7 socket 86…

If K7 powers on it uses power from CB78 to feed thru the contacts of relay K8, the high/low beam relay. K8 being on = high beam, otherwise low beam. K8 is controlled by the column switch. From there it feeds on to the lights. You can pull out K7 and jumper the socket pin 30-87, and the headlights should come on to test that part of the circuit.


View attachment 862257

This was great help! Thanks. Got everything situated.

 

[Ronmar]

This was great help! Thanks. Got everything situated.

What was the problem?

 

[Erik Erickson]

Just a relay. Jumpered K7 then K8 started working. Need a couple headlights too.