No rear marker lights power

[Towbarman]

Good morning
My issue is, I have power to my headlights, turn signals and front amber lights. I have rear taillights and blinkers, but no power to the rear red marker light. I took my multimeter to check for power and nothing. Checked breakers seems to be okay. What is my problem. Thanks, TowBarman

 

[GeneralDisorder]

Probably grounding. But we have no way to know - you will have to go through the schematic and test:

FMTV Schematics A 0 A 1 R : Stewart and Stevenson : Free Download, Borrow, and Streaming : Internet Archive

Family of Medium Tactical Vehicles wiring schematics. A0, A1, A1R WTEC III, A1R Gen IV

archive.org

 

[Ronmar]

Good morning
My issue is, I have power to my headlights, turn signals and front amber lights. I have rear taillights and blinkers, but no power to the rear red marker light. I took my multimeter to check for power and nothing. Checked breakers seems to be okay. What is my problem. Thanks, TowBarman

year and model? pushbutton or 3 lever lightswitch?

So taillights, brake and turn but no rear markers? Hmmm do the reverse light work? All the rear lighting grounds thru TL 97 which is located I think on the drivers side frame to the rear of the axle under a 10Mm bolt. if the other rear lights are OK, the ground probably is as well.

taillight and marker power both originate at k20, with the taillights passing thru CB80 and ALL the markers passing thru CB67. so if the front markers are OK then CB67 must be OK.

Marker light power from CB67 feeds TB1 pin 1-26, with only 10 different circuits connected to that group. Where the rear markers become distinctly separate is at TB1 pin 11. perhaps you have an issue there and the wire has been pulled out/disconnected at TB1-11. from 1-11 it goes to j51-7 also in the passenger dash near the power panel. from there it is straight back to a mass junction point E21 buried in the wiring harness just forward of the pintle hitch where it splits to feed the 7 rear marker lights... Now of course this is specific info for a A0, but these trucks are very similar IRT basic light wiring...

 

[Towbarman]

Good morning gentlemen. I say that loosely of course. I'm reporting back on my issue with the rear markers and the middle rear marker lights. It has been a hassle chasing wires. I stared from the back where the markers are. I checked the power of course, taillights work, 4 ways work, but still nothing else. I found both of the ground wires on the frame. Cleaned them up and still nothing. I kept on going down the harness and testing for power. I have power on wires 489T, 21, 489G,461BA, 1404, and 461B. 6 out of the dozen wires I checked but nothing what I'm looking for. I did a continuty check on the circuit breakers, CB67 is good. I have checked in module 3 where the rear markers are circuit breakers good but when I put my test light to check for power, there was no power. I need help badly. My boss has been out of office for 3 weeks and will be back Monday. He will ask what the hell have I been doing, Any more help will be appreciated. Thanks Torbarman