Humvee m998 start problems after installing a plug and play ignition switch

[HumveeM998]

Hey guys I'm new here and new with humvee. I just picked up a 1988 humvee m998 with 6.2. Well I got one of those plug and play key ignition switch and after I installed it the truck won't start, not even a click. The wait light comes on and then goes off, but no start after. I installed the old switch and the same thing. Ran fine before this, are there fuses or anything that could have popped with the aftermarket ignition switch. Any help would be perfect thanks!

 

[hummer4x4guy]

Did you disconnect the batteries when you installed the new switch? The trucks can be picky if you don't take the batteries off line before doing any electrical work.


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[HumveeM998]

No I didn't do that, I just installed 2 new batterys before this and then did the switch. What should I look for now that I didn't disconnect?

 

[hummer4x4guy]

Someone else might have a better idea of what to look for. But from now on always remove one of the battery cables anytime you plan to unplug or plug in anything.


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[HumveeM998]

Will do, thanks

 

[HumveeM998]

When I do try to start the truck is do hear a click on the top side of the motor. Maybe a starter relay, but haven't looked yet.

 

[dilvoy]

Make sure you have the shifter in neutral. I made a switch for myself with a switch that I got off of Amazon.com for about $12 delivered. Figured out the wires.

11A 24 volt battery
29A Run
14A Start
My switch also had an acc postion too.

Put it in and then tried to start it and no cranky. Checked the wire connections three times and still no go until I sat in the vehicle and looked at the shifter and it was in reverse, where I kept it as a sort of anti theft measure. Popped it into neutral and all was well.

 

[kfrosty]

Definitely check neutral as has been mentioned. If not that then start working your way backwards. If you have a friend, get a volt meter and put the positive on the "ignite" wire on the starter solenoid. (On mine there are 2 small wires that come together and you can access them easily under the truck.)

Have somebody try to start and see if you have voltage there. If so in my case it was my starter.

FYI. I got my truck and new batteries and it started better than any vehicle I've owned for a week. Then all of a sudden nothing. It turned out I think I had a dirty connection somewhere. So I disconnected the batteries and cleaned ever single connection. Since I was doing that I even made the "Octupus" grounding harnessed mentioned here multiple times.

If you don't get power to the solenoid wires, then what I did is take a piece of wire and connect one end to the positive on the battery and tap the other end to the same solenoid wire just to:
1. - See if the starter would bump.
2. - If it bums with the ignition on, I would see if it would start. (Don't do it too long.)

If it bumps or turns over and wont start, them my guess you have either something with the switches hooked up backwards or there is something with your Control Box under the drivers dash. I'd get a spare just to test, but again as everybody has suggested make sure the battery is disconnected and use your original switch and MAKE sure you have it hooked up correctly. (Hopefully you taped or marked the wires before you removed the original ignition.)

The "clunks" you hear are most likely coming from the control box. Control box is either a PCB, EESS or a S3 Smart System Start.

Where are you at in NC? I have the older Prestolite, PCB box I replaced in mine with an S3 controller.

Also, my old prestolite PCB would clunk as soon as I switched to start, my Solenoid wires had power and how I knew it was the starter. However, if you're just holding it on start and you hear intermittent clunks while holding it in start, I think that has something to do with the glow plugs. Mine did that as well and I could see the alt gauge jumping back and forth.

 

[papakb]

The 11A lead is power to the start-run switch, the 29A lead feeds power back to the PCB in the run position and the 14A switch sends power down through the neutral safety switch to the starter. With a voltmeter you should be able to see if you get +24v on the 14A lead when you turn the switch to start. If you get voltage there the problem is downstream to the shifter or further down to the starter.

Kurt
KG6KMJ

 

[hummer4x4guy]

Or you can just replace the stock switch and remove the screw for the lever and pop it off when ya leave the truck. In 15 years I've never had anyone mess with my rig.


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[NormB]

Or you can just replace the stock switch and remove the screw for the lever and pop it off when ya leave the truck. In 15 years I've never had anyone mess with my rig.

Hmm...

 

[NormB]

Zombie post warning:

Changed out batteries a few weeks ago - optima yellow tops, I've posted pics elsewhere - truck fired RIGHT up. What is that, 1700 CCA? Compared to the date-code label-less toyota batteries with a combined 750 CCA the seller put in there (I knew I'd need upgrades), wowza.

Until last week. Turned ignition to wait, wait light went out, no start. Tried again... again... checked shifter to make sure it was in neutral, tried again and VROOM!

Took it for a ride, let my son drive it around, backed it into the driveway, got a few minutes today, thought I'd start it up, and nothing.

Wait light goes out, NO noise at all when I go to start. Turn lever BACK and I hear two distinct clicks, one softer, one more solid.

I'm guessing here, but I think the neutral switch is toast.

Do I:

1 - disconnect and try to start, or

2 - jump the leads and start.

Is the switch normally OPEN, or normally CLOSED?

I've spent maybe the last half hour looking at the manuals I've downloaded and I can't find the shifter/neutral safety switch circuit. Forget Bing/Google, "M998 [or HMMWV or HUMVEE] neutral safety switch schematic/circuit/wiring diagram" yields very little that's useful, nothing specific, and a heck of a lot of extraneous motorcycle and other schematics.

So, back to Steel Soldiers.

I'm a couple days this weekend and it'll be raining/ice storming, but I should be able to poke around under the truck a bit, hopefully enough to figure out if the neutral switch is involved and take it from there.

Have yellow label EESS if this adds anything.

Thanks in advance.

Norm

 

[jeffy777]

I am not sure your neutral switch is at fault by what you are saying. You probably have a battery leak somewhere.

I left the switch in this position and after a couple of days batteries were a goner but the wait light went through the progression of acting like it would start, but it did not.

I have read several there is a lot of grounding issues with our HMMWV's.

If you have a 24 Charger/Starter it will help you know the if the issue is with a drain.

Then also another guy on the board did not tighten a post as he changed batteries and it gave similar symptoms(not saying that is it).

Just throwing out ideas...

I would think if you disconnect and try. Then jump and try you will answer your question without reference as it is a simple binary option.

Good luck.

 

[Retiredwarhorses]

There are only 3 wires on a shifter, the one for the back lighting has a red tie rap on it, the other 2 are the NSS.
the NSS screws into the right side of the shifter and the wire protrude out of the boot, just unplug them and
loop the 2 wires at the harness back to each other, just remember...this is a very dangerous condition, this truck will start in gear!

 

[diesel dave]

Your "start-doesn't start" symptoms sound like a loose wire/connection to me. Start at the main battery terminal connections where the battery cables attach to the main harness and work forward.

 

[NormB]

There are only 3 wires on a shifter, the one for the back lighting has a red tie rap on it, the other 2 are the NSS.
the NSS screws into the right side of the shifter and the wire protrude out of the boot, just unplug them and
loop the 2 wires at the harness back to each other, just remember...this is a very dangerous condition, this truck will start in gear!

EXACTLY the answer I was looking for. EZPZ. I'll do that second.

 

[NormB]

Your "start-doesn't start" symptoms sound like a loose wire/connection to me. Start at the main battery terminal connections where the battery cables attach to the main harness and work forward.

Yeah, curious that this started RIGHT after I put new batteries in.

Working voltage was 25.2. At full charge I was showing 25.8V having the system on a solargizer 24v charger (plugged into slave port - I pull it when I'm going to start the beast), I DID have the light switch in the "DIM" position for 2 weeks, which might account for the slow drain, but that's still a heck of a lot of CCA.

This "started" right after I reconnected the batteries AND installed the grounding harness. I DID clean all contacts - used a scotchbrite pad and acetone and Deoxit - connections SHOULD be solid.

When temps get back above freezing (my garage is full of sound/audio gear) I'll recheck all battery, starter and ground connections, neutral switch last, although the fact it DID start after jiggling the shifter in-out of neutral last week is very suspicious.

Of all OEM HMMWV parts, I find the fact the neutral safety switch is VERY cheap (I've seen 'em 3 for $12) very suspicious for this being a high-failure/low MTBF part though.

Thanks again. I'll get back to you.

 

[fllaw1]

here is your 3 off the shifter

 

[NormB]

here is your 3 off the shifter

View attachment 658195

Been there, seen that, looks a LOT like mine.

I blew about $30 and bought the gaskets/rubber boot to replace it all when I open it up eventually to clean/lube. Switch I don't have, but will troubleshoot shortly.

 

[Action]

Leaving the left switch on dim or bright does not turn anything on or drain the batteries. when the middle lever point straight up, all lights are OFF.