Here's a funny electrical gremlin on my new HEMTT!

[dma251]

I discovered this yesterday while messing with the light switch and scared the bejesus out of myself! When I switch the main headlight switch all the way on - the engine starts! Whether the key is switched on or not. I'm thinking someone accidentally got a wire crossed when they wired in the ignition switch. I realize this is generally a fairly easy to diagnose problem, but I was wondering if maybe one of you guys has a quick answer to what it might be.

 

[Rattlehead]

It's probably due to the black wire hooked up to the wrong circuit

Seriously, I don't have any ideas other than what you are suspecting.

 

[Jones]

Uhhh, NOT the way it should be. The underdash wiring is a basket of snakes and you might have a couple of wires that have the insulation rubbed off of them in just the wrong spot. I have the wiring diagrams for the HEMTTs and LVSs. PM me and I'll see if I can help.

 

[devilman96]

@ black wire!

 

[cranetruck]

... When I switch the main headlight switch all the way on - the engine starts! Whether the key is switched on or not.....

"all the way on" ?? Which truck? What key?

 

[dma251]

... When I switch the main headlight switch all the way on - the engine starts! Whether the key is switched on or not.....

"all the way on" ?? Which truck? What key?

Yes, whether the key is turned on or off, in the ignition or not, if I turn the light switch to headlamps on, the truck engine fires up. I can't tell if it's holding the starter on or not, since I shut it down as soon as it does it.

Yes, I realize it didn't come from Oshkosh with a keyed ignition switch. That was obviously added on by one of the previous owners, which is probably my problem right there. I figure someone probably has inadvertantly wired the two systems together.

(It's my M977 HEMTT, by the way)

 

[alphadeltaromeo]

... When I switch the main headlight switch all the way on - the engine starts! Whether the key is switched on or not.....

"all the way on" ?? Which truck? What key?

(It's my M977 HEMTT, by the way)

I think you have a defective M977. It's probably best if you drive it to GA and I'll take it off your hands to avoid any further issues you may have with it...

 

[dma251]

RE: Re: Here

I believe I found the problem. Disconnected cab ground strap. When I was reinstalling the air horn under the cab I found the cab to chassis ground was disconnected. After hooking it back up I tried out the headlight switch - no start! Just the way it's supposed to.

After that I had to take it for a spin around my neighborhood just for fun. I have about 20 tall speed bumps in my neighborhood - this truck takes those speedbumps so easy you don't even feel them. Huge difference from my 5-ton, HUGE.