HMMWV Doesn't Shut Down With Ignition Switch

[hawk-aggie]

NOTE: I'm going to be using the term "smart" box in referring to the EESS. Don't get twisted about semantics.

Our 1994 M1097 that I'm working on has an electrical issue. Engine is 6.5L, transmission is 3-speed, “smart” box is Natron, new starter, new batteries, new glow plugs, new glow plug controller, professionally rebuilt fuel injector pump, and auxiliary grounding harness.

I have disconnected many wires and cables - one at a time - to try to isolate the problem. The only thing I haven't done is disconnect any of the wires/cables on the 200A alternator or the voltage regulator. I have also been pouring over the wiring diagrams without positive result.

When I first connect the batteries, I get a significant spark at the ground post when the negative cable is connected. I've seen a small spark on most of our HMMWVs, but this is significantly different. It's not a big spark like you might see with a short. It's like something has its 'switch' permanently closed, causing a spark when the negative cable is connected.

I follow the normal starting process. I turn the ignition switch to run (I can hear the solenoid in the “smart” box clunk on). The wait light stays on about 8-12 seconds. Engine cranks strong. When it catches, the voltmeter is on the tick mark in the green zone – voltage checked with a multimeter indicates 28.4 volts. Oil pressure is just over 30 psi.

When I turn off the ignition, the engine does not shut down until I pull the lead to the fuel cutoff solenoid. When the ignition switch is turned off, the "smart" box relay does not go "clunk" as it should. The power on the fuel cutoff solenoid lead is still active and the "smart" box relay, and the voltmeter registers in the middle of the yellow band. When I then disconnect the battery, I hear the “smart” box relay clunk off, and the voltmeter needle drops to zero.

I don't believe this is a "smart" box issue. I have installed six (6) “smart” boxes so far during testing. I know now that "smart" box number 1 has a burnt/fried component (cause unknown). Boxes 2 - 5 are green label KDS. Issues inside them are unknown at this time. All had the same results as indicated above. The only difference between them is the wait time - from zip to quick flash to 8-10 seconds. The only reason the Natron is installed is that the engine fired right up without a lot of cranking.

My buddy and I are not on the same page. He thinks the issue is the smart box. I think there’s a wiring issue that keeps power to the smart box relay solenoid even after the ignition switch is turned off. We are open to ideas and consultation for fixing this truck.

 

[Mogman]

Pulling the connector on the regulator would have been the first thing I would have tried.
Disconnecting wire 29A off of the master start switch would have been second.
If you have changed six smart boxes it seems very doubtful it is a smart box.

 

[NDT]

Ignition switch is bad.

 

[hawk-aggie]

Ignition switch is bad.

That's what we thought. Switched it out. Same results.

 

[hawk-aggie]

Pulling the connector on the regulator would have been the first thing I would have tried.
Disconnecting wire 29A off of the master start switch would have been second.
If you have changed six smart boxes it seems very doubtful it is a smart box.

We are in agreement regarding the smart box. It is my buddy who went down that trail. I keep veering away from an issue with the regulator, because the voltage output is right on the money. I will try your suggestions. Thanks.

 

[Milcommoguy]

Did you ever have the truck working correctly?

Got to start from a know starting point, CAMO

 

[NDT]

Ignition switch miswire?

 

[hawk-aggie]

Ignition switch miswire?

No, verified. Also, tried another ignition switch with same result

 

[hawk-aggie]

Did you ever have the truck working correctly?

Got to start from a know starting point, CAMO

This was purchased as a non-runner by the museum where I volunteer. Just got it running this past week.. So, the answer to your question is "no, sir".

 

[Milcommoguy]

This was purchased as a non-runner by the museum where I volunteer. Just got it running this past week.. So, the answer to your question is "no, sir".

If I understand the response to be "NO" as this is an important starting point with the crazy symptoms.

Got a non runner , but got it running, wont turn off unless one pulls the 5A lead on the fuel cut off solenoid.

Walking it back ... all the obvious connections stated, switch, boxes, alternator and the like covered. ? Factory wiring, NO modifications / hack job going on? I would... and I think you'er wondering what is holding the fuel solenoid energized.

More data time. Monitor the 54A lead (tap into it) while properly connected. Would be interested in the voltage in all states, STOP, RUN, STARTing and back to Stop.
I would like to know the condition of the engine and body connectors ? Rusted, busted, corroded can be suspect. Pictures helpful.

These type of problems are going to require eyes on all connections with prints and understanding. Some obvious and looks like you have ruled them out
? The many box swaps is interesting... BUT then, I am NO fan of smart anything LOL.

HumV wiring is pretty straight forward. Harnesses are well made. One thing that is a bit to troubleshoot is there are splices internal to the design. This make it a little tricky to isolate individual circuits feeding... in this case the IP, but other components share the same. Look at the fan control, TDM, TSU and even the "BOX" We all know those boxes fail and everything goes thru it.

More history of the rig is helpful or just jump in and follow the trail to a can of worm... then success.

I don't like to guess this or that, poking and pulling wires might work???

That's what the Dr. does when one is up on the table, CAMO

>>>>> HUMV ________OWNER >>>>>>>>>>> Good Luck

 

[hawk-aggie]

If I understand the response to be "NO" as this is an important starting point with the crazy symptoms.

Got a non runner , but got it running, wont turn off unless one pulls the 5A lead on the fuel cut off solenoid.

Walking it back ... all the obvious connections stated, switch, boxes, alternator and the like covered. ? Factory wiring, NO modifications / hack job going on? I would... and I think you'er wondering what is holding the fuel solenoid energized.

More data time. Monitor the 54A lead (tap into it) while properly connected. Would be interested in the voltage in all states, STOP, RUN, STARTing and back to Stop.
I would like to know the condition of the engine and body connectors ? Rusted, busted, corroded can be suspect. Pictures helpful.

These type of problems are going to require eyes on all connections with prints and understanding. Some obvious and looks like you have ruled them out
? The many box swaps is interesting... BUT then, I am NO fan of smart anything LOL.

HumV wiring is pretty straight forward. Harnesses are well made. One thing that is a bit to troubleshoot is there are splices internal to the design. This make it a little tricky to isolate individual circuits feeding... in this case the IP, but other components share the same. Look at the fan control, TDM, TSU and even the "BOX" We all know those boxes fail and everything goes thru it.

More history of the rig is helpful or just jump in and follow the trail to a can of worm... then success.

I don't like to guess this or that, poking and pulling wires might work???

That's what the Dr. does when one is up on the table, CAMO

>>>>> HUMV ________OWNER >>>>>>>>>>> Good Luck
View attachment 952733

This truck is straight from the military through only one stop (our resource). We don't make modifications to our trucks. We buy them, use them for a minimum of 18 months, then sell them as an alternate income stream for the museum. The less time and money put into each truck to get it into service, the better. We've had this truck since 06/22. It had been sitting out behind one of our buildings with 4 others, waiting for its turn. We sold off 3 trucks in "as-is" condition, so this one and one other moved up in the queue. I'm the only one working on these, and I've got 3 other runners, and an M35 and 4 generators to keep up.

This truck does not have much rust. When we got it. the alternator was in the front floorboard, the belts were missing, as was the hydraulic line to the radiator fan, and the headlights. Other than that, I've only changed the hood to match, and installed a working wiring harness for the front lights.

I'll see about getting some photos.

 

[TOBASH]

Tried disconnecting the plug on the PCB box under the dashboard. If your vehicle stops, then the problem is possibly the cut off on the IP.

Check my signature line on how to properly rebuild a Nartron box. It’s easy.

Feel free to contact me via private message for instructions. I’ve helped many people rebuild their boxes.