Fire Dept Needs Help

[Chief 15]

Good afternoon. Our volunteer fire department has a M1078. One of our folks left the ignition switch on, and of course that killed the battery. We use two 12-volt batteries to power the truck. They were disconnected and charged separately; however in the process, the charger was put on the wrong terminals when they switched to the second battery, and something blew. There is no power now. Is there a main fuse we can check? We need the truck for a Toys For Tots event.

 

[NDT]

What year model is the truck? Need to know that to diagnose what all to look at.

 

[Chief 15]

1997 S&S / BAE M1078 A0

 

[NDT]

Ok. You mentioned batteries were disconnected for charging. Is this correct? If only the single battery was reverse polaritied, then that battery is shot. Check both batteries for voltage to start with.

 

[Chief 15]

Both batteries tested as OK. We tried the ignition switch a few minutes ago and it powered on, but there was a definite electrical "sizzle" in the circuit breaker area behind the passenger dash.

 

[Xengineguy]

Both batteries tested as OK. We tried the ignition switch a few minutes ago and it powered on, but there was a definite electrical "sizzle" in the circuit breaker area behind the passenger dash.

Look for a loose connection behind the fuse panel. Big wires work loose over time.

 

[Ronmar]

Well the charging backwards is one issue, but this almost sounds like the batteries were not installed correctly.

Define “tested as ok”. Voltage, or voltage under load. Do they pass a CCA test? Not ok untill it holds a load with acceptable volt drop.

as mentioned, check connections. Under load the voltage at the power panel test points should be no more than 3% lower than the voltage at the batteries with the same load. IE: all the lights turned on, measure battery voltage and power panel voltage. Bad connections are common on the polarity device inboard of the spare tire since those are out in the weather. A bad connection will pass full voltage untill you try and pull some current thru it, so voltage is not good until tested good under load…

A basic lower rate load tester, 75-100A can do this properly at the power panel test points.

 

[NY Tom]

He might be saying that they connected the charger to the truck instead of the batteries.

Sounds like the batteries were disconnected and charged in the truck. I have nothing more to add but perhaps this will help the others come up with ideas.

 

[coachgeo]

Anyone know where in the TM's there is discussion on the Reverse Poloarity Box.... what to do when reverse polarity occurred?

 

[Guyfang]

Good afternoon. Our volunteer fire department has a M1078. One of our folks left the ignition switch on, and of course that killed the battery. We use two 12-volt batteries to power the truck. They were disconnected and charged separately; (If the batteries were disconnected, when you charged them, Its hard to damage the truck electric system. Or am I missing something here?) however in the process, the charger was put on the wrong terminals when they switched to the second battery, (Were the second battery terminals hooked up to the charger? Or did someone hook up the charger to the truck wire harness terminals?) and something blew. There is no power now. Is there a main fuse we can check? We need the truck for a Toys For Tots event.

 

[NDT]

Parts that might be smoked due to reverse polarity: alternator, alternator regulator, TCM (transmission controller located with keypad), transmission VIM (vehicle interface module located under PDP power distribution panel).

 

[GopherHill]

I know this isn't really useful but..
This is one of the few drawbacks to using military equipment in volunteer fire departments. Personnel need training using these trucks but probably won't get it or won't pay attention. I made a cheat sheet for our M35a2 but still only a select few are allowed to drive it. Just my opinion.