M1089 Dashboard Intermittent Power

[firebirdgm2000]

I have a 1089A1P2 FMTV Wrecker that has been having issues with the dashboard connection going on and off. All the gauges reset or turn off completely for a short duration (this includes the air gauges ) and continue to operate for a random amount of time.

Parts replaced and checked so far:

Batteries checked and charged
Charging system checked
Checked harness behind dash
Lug behind dash cleaned and regrounded
LBCD replaced
Interconnecting box behind dash replaced

 

[NDT]

Welcome. Look for chafing on the wiring behind the dash. On the soft skin trucks, the gas pedal linkage would wear through the harness and cause shorts only if you were on the gas. Not sure if the armored cabs have this problem or not. The on - off cycling sounds like the breaker resetting. Good luck.

 

[coachgeo]

Welcome. Look for chafing on the wiring behind the dash. On the soft skin trucks, the gas pedal linkage would wear through the harness and cause shorts only if you were on the gas. Not sure if the armored cabs have this problem or not. The on - off cycling sounds like the breaker resetting. Good luck.

Have read of this issue before.... hopefully not hijacking this fellows thread..... are you referring to any wiring that may go thru the same access hole in floor of dash as the rod from pedal travels? Curious on this cause I've no wire harneses thru that hole on mine. Just wonder if some trucks had a wire harness run thru that hole and some didn't.

 

[firebirdgm2000]

I've jiggled the harness without any change or effect its just completely random, i'm starting to think this may be coming from the breaker box so I may be pulling that up soon to check the wiring from underneath. One other thing ive noticed is the 12v side keeps dipping below 12v but all the batteries are fully charged beyond 12.7.

 

[Suprman]

Maybe the polarity box. Under the spare tire. Works with the regulator to control charging and cab power from the batts go thru it.

 

[firebirdgm2000]

Maybe the polarity box. Under the spare tire. Works with the regulator to control charging and cab power from the batts go thru it.

I have already replaced this box, still have the same issue.

 

[Suprman]

Grounds under power panel bolted up on the right side. On a bolt that holds on the passenger dash grab handle. Does the truck die too?

 

[Ronmar]

What year? Are these individual gauges(each gauge receives power and is connected directly to its sensor) or are they bussed gauges connected to a MMDC?

On an A0 with individual gauges, each gauge receives power directly from the instrument circuit breaker CB77.

On the later A1’s the gauges are all connected to a data bus which connects to the Module Data Computer Instrument(MMDC) which is connected to all the gauge sensors... one of those receives power from CB-76(ignition 12v) and CB-38(battery 12v)...

i am not sure what year/model they switched to the bussed gauges and processor...

 

[Suprman]

Its a c7 with data bus. Gauges are controlled by the cat ecm