1996 LMTV 1078 cab has not power

[ReaperOftexas]

Hey y'all need a bit of help I work with Harris County Sheriff Office out of Houston Tx we have alot of LMTV for our high water rescue. Anyway I have an M1078 for some reason the cab will not power up at all. I've check the batters, cables, test the LBCD and cleaned it, test fuses check the solenoid what Am I missing. Again its a 1996 M1078 thanks for y'alls help

 

[NDT]

Can you verify what year you have? 1996 trucks do not have LBCDs. If it’s a later model (A1) truck that does indeed have LBCD and solenoids at the battery box, the recommendation it to remove the solenoids and jump past them. This typically fixes this issue.

 

[Ronmar]

Did y0u clean all the grounds? Starter to frame, alt to frame, right frame to cab behind grill. Those are the 3 biggies but there are more…

96 has a polarity protection device, PPD, not a LBCD. Open the power panel dash cover. three round test points on the left, ground, 12 and 24v. Measure voltage there. Keep measuring there and turn on the switch. Is voltage still present? Voltage is not good until measured under load.

On the 98 it uses 12v controlled by the ignition switch to control the 24v ignition relay K2, so no 12v, no 24v ignition power…

 

[ReaperOftexas]

This what I have

 

[Ronmar]

The dash test points are designated X1, X2 and X3. Here is a simplified start circuit diagram that shows the basic ignition power circuit.

all this relies on good solid power and ground connections between battery terminals and X1-X3. Also why y0u measure circuit voltage under load. A bad connection can still pass full voltage unloaded, but the voltage will disappear when a load is applied. Like a kink in a garden hose, you will still see full pressure at the end nozzle untill you open the valve at the nozzle, it will spurt briefly then fall to a trickle. This can often cause relay circuits to pulse.

the polarity box is a great starting point as those connections are out in the weather and often a cause of dash power feed issues, but the grounds are equally as important, often overlooked and typically terribly done from the factory(full of paint and relying on janky star washers to complete the circuit…

Good Luck.

 

[NDT]

HCSO Eye candy while you are busy diagnosin’

 

[ReaperOftexas]

I will go head and try these steps thank you

 

[ReaperOftexas]

HCSO Eye candy while you are busy diagnosin’

That is the LMTV I'm working on now lmao Deputy messed her up!

 

[ReaperOftexas]

Got damn lol

 

[Ronmar]

I work for a Sheriffs Department also we don’t have any LMTVs though…