A2 M1123 - Troubleshooting Stop Lamp Switch

[MaverickH1]

My wife drove the M1123 for the first time today, which means I got to follow this truck for the first time today. Let me just state the obvious and say WOW it's a cool looking truck. It's funny how much different they look when they're actually on the road. Also, she loved driving it.

What this also means is that I was able to see very clearly that the brake lights were no longer working. It was working as late as January, but not now.

Coming out and playing with it, it seemed like it was just out of adjustment. No problem, I followed the TM and attempted to adjust it to work properly. No dice. It was as if it needed to be adjusted beyond the adjustment slots available. I decided to add spacers via washers to increase the distance from the pedal linkage to the linkage on the switch. This worked well for the continuity test. I adjusted it perfectly so that continuity on 75B and 75A indicated a closed circuit just past the initial play of the brake pedal.

However, when putting the wires back together everything was inoperable. But... when I push on the pedal with my foot and reach down and push the switch linkage a little, I get full brake lights. I pulled it apart and started tracing voltages. Everything checked fine. I had my wife come out and check to see if the lights were dim. Turns out they were before I manually activated it with my hand.

So in summary... I believe the continuity test is passing the switch and the adjustment... and the voltage tests are passing everything... but there must be something internally that does not allow full amperage to be transferred due to weak contact.

I thought maybe something downstream was playing a role... like wire 75A ends up carrying the current back to the main light switch which gets rerouted to a neutral position box or something according to the wiring diagrams... but to me none of that would be suspect if I can manually manipulate the stop lamp switch to work.

Has anyone messed with these switches? Can anyone find a fault in my logic that the switch is in fact bad and needs to be replaced?

Thank you!

 

[86humv]

You probably need another dual switch.
The brake switch in that dual assembly do go bad.....had many.
If you have to adjust it past the factory settings...its probably bad.
Take switch off....remove the screw and spacer to the two levers, and check brake switch.....S/B spring loaded and travel nicely.

 

[Action]

Turn lights on.

 

[MaverickH1]

Turn lights on.

Ha! I made sure about 27 times that the lights were in fact on.

I'm guessing it is an internal issue like the contacts are not making solid enough contact to transfer full amperage. Replacement switch was ordered from Kascar, hopefully it shows up tomorrow and I can get it installed for the thing I wanted to do Thursday evening.

 

[papakb]

The design of the brake light actuator switch in the HMMWV is a joke! There's no adjustment other than the position of the switch and there's NO free throw adjustment of the linkage at all. Just a simple linkage between the pedal and the switch. So when you actuate the switch by hand your pushing it down into an area where the contacts are still in good shape giving you full brightness brake lights but if you did that driving down the road you'd be standing on your head! The original switch is the same as that used in the M151 and as it ages, it burns away the electrical contacts every time the lights come on so after a number of years the contacts are worn and resistive and that translates into dim brake lights or none at all. Since there is no free throw adjustment on the linkage all you can do is to replace the switch. Incandescent bulbs draw a lot of power and wear the switch after a few years of use. Changing to LED bulbs that draw much less power and will make your replacement last virtually forever.

Kurt

 

[MaverickH1]

Got the new switch in, installing it still didn't have it positioned correctly. I ended up having to add two washers as shims on the bolts closest to the firewall and one washer on the other. The washer was placed between the switch's flange and the mounting flange. This basically moved it further away from the brake pedal linkage and brought the adjustment slots into an area where I could actually adjust it out of spec both ways. I did this with the old switch too in order to pass the continuity tests.

So the old switch was definitely bad. As with all things electrical I remove from the HMMWV, I snip the cords and keep the connectors so I have the ability to solder and make these connectors for free.

I will look into adding LEDs to reduce the amperage that goes through the switch. It SHOULD be as simple as a bulb change... but it might be more difficult than that with the turn signal flashers.

I used to consider leaving the light switch on "Stop Lights" all the time just in case I forgot to turn the lights on one day while on the road... but with how squirrely this switch is I don't trust it to not accidentally activate full time brake lights and drain the batteries.

Thanks for the help, everyone!

 

[Retiredwarhorses]

I've had more Hmmwv's then I can count ..I've had very little issues with the switch.

 

[MaverickH1]

After replacing and adjusting the switch, the problem went away. I tested it a few nights after replacement and it seemed to be doing well. Then I noticed that with the light switch on Stop Light, there was a dim glow from the brake lights. I figured the switch was out of adjustment and adjusted it again. The problem seemed to go away, but it's difficult to test it with just one person.

I switched to LED bulbs all around to reduce amperage on the system and increase visibility. The dim problem still exists.

I'm starting to believe that there is something wrong with the turn signal switch or possibly grounds.

When you turn to stop lights, sometimes the brake lights will come on fully. Sometimes dim. Sometimes not at all. If the brake light switch is activated, the turn signal switch should receive that signal and override the hazard lights. But when you put the hazard lights on the hazards would flash and the brake lights would still glow dimly. That makes me think the power to the brake lights is not coming from the brake switch itself.

Although LEDs screw up systems left and right, there's something screwy whether it's LEDs or not.

I'll be testing it to see what's up.

The electrical problems continue!

 

[Action]

Back the humvee up near s wall at night to test rear lights by yourself.

 

[MaverickH1]

Back the humvee up near s wall at night to test rear lights by yourself.

Oh, of course! A lot of the troubleshooting has been during the day, and I've had to come up with some interesting tactics. Once I hung my sunglasses in a tree so I could see the lights in the reflection. And once I put my phone on the ground leaning against a bottle with the screen facing me and the screen side camera on so I could see the lights.

It's been an adventure.

 

[MaverickH1]

Electrical stuff is crazy.

As of this morning, I had 4 electrical lighting problems. Almost all intermittent.

1) Brake lights functioning erratically.
2) Front left marker light not functioning, sometimes.
3) Hazards stay on fully. Sometimes. Likewise turn signals would act strange.
4) Running light on left rear was dim, running light on right rear was off.

So today I set out to work on it. My wife was doing yoga behind the Humvee to tell me what lights were on or off. Long story short:

1) Both running light LEDs that I replaced a few days ago were broken somehow. The one on the right looked like it arced out of the housing and was completely inoperable. The running light LED on the left only dimly lit 7 of the 21 LEDs on its circuit board.
2) The brake light switch was closing if the pedal was hit side to side. It was very sensitive to this. I had added washers to move the switch further from the brake light to give it more room to adjust. I think this stretched it side to side also and caused the problem.

I think the broken LEDs were sending voltage somehow and somehow causing all of the other problems. Changing two bulbs back to incandescent and returning the brake switch to factory height and adjusting per the TMs appears to have fixed everything.

 

[fpchief]

I've had more Hmmwv's then I can count ..I've had very little issues with the switch.

Yea old thread....
if you had little issues with the switch, what was usually the issue if there are no brake lights? This is on a M1097A2..

 

[Coug]

Yea old thread....
if you had little issues with the switch, what was usually the issue if there are no brake lights? This is on a M1097A2..

on mine right now unless I press down hard I have no brake lights. Need to adjust the engagement switch that hooks to the brake pedal.
If it's just no brake lights that's a good place to start. If other lights aren't working as well then start looking more at the switches, wiring, and bulbs.

 

[fpchief]

Yea I have gone over the easy stuff so far... been reading that the adjustment is kinda hit or miss but will definitely give it a shot. Wiring so far is looking 100% intact and pretty much brand new from rebuild. Kinda OK for SF-97's to take so long...for me anyway....gives me plenty of time to fix junk like this...

 

[Coug]

Yea I have gone over the easy stuff so far... been reading that the adjustment is kinda hit or miss but will definitely give it a shot. Wiring so far is looking 100% intact and pretty much brand new from rebuild. Kinda OK for SF-97's to take so long...for me anyway....gives me plenty of time to fix junk like this...

yeah, but downside of SF-97 taking so long in some places is not wanting to dump money into the truck until you know it's licensed.

 

[Chief B]

For what it is worth... When I first got my HMMWV, the brake lights would not come on unless I had brake pushed all the way in. Problem was that by that time I was already at a complete stop so nobody behind me knew when I was slowing down to stop. For me it was a simple adjustment of the switch, it had been put in pushed all the way forward preventing it from engaging unless pedal was all the way in. I adjusted it all the way out then gradually pushed it in until lights shut off then tightened it up and no problems since.

 

[Retiredwarhorses]

Many of the switches are out of adjustment, the early switch just controls brake lights, the A2 lights and
torque converter unlock. I’ve had Adjust almost half the trucks I’ve receive as TC won’t unlock.
its a PITA to get spot on sometimes.

 

[fpchief]

Slid it fully both ways and spots in between. Cant get no stop lights. Can I reasonably assume it is the switch?

 

[Coug]

Slid it fully both ways and spots in between. Cant get no stop lights. Can I reasonably assume it is the switch?

Unless you are testing it for continuity using a meter and have the switch isolated, all that tells you is that the brake lights aren't working.

To use a household wiring example, you walk into a room and the lights don't work. Flicking the switch on and off isn't turning it on, so you're deciding it must be a faulty light switch, when it could just as easily be burned out lights, a loose wire at the light socket, or even a burned up wire between the breaker panel and the switch. Without determining that power is reaching the switch, and then seeing if power comes out of the switch when activated, it could still be anything at all, just flicking the switch doesn't change that.

If there is something else in the system preventing the lights from working, then it doesn't matter what position the switch is in.



Unless you want to just throw money at the problem and hope it fixes it, you WILL need some way to check components individually.

 

[fpchief]

Unless you are testing it for continuity using a meter and have the switch isolated, all that tells you is that the brake lights aren't working.

To use a household wiring example, you walk into a room and the lights don't work. Flicking the switch on and off isn't turning it on, so you're deciding it must be a faulty light switch, when it could just as easily be burned out lights, a loose wire at the light socket, or even a burned up wire between the breaker panel and the switch. Without determining that power is reaching the switch, and then seeing if power comes out of the switch when activated, it could still be anything at all, just flicking the switch doesn't change that.

If there is something else in the system preventing the lights from working, then it doesn't matter what position the switch is in.



Unless you want to just throw money at the problem and hope it fixes it, you WILL need some way to check components individually.

I obviously wasn't very clear on what I had already done...yea there is power. It is troubleshot to the switch , however just ensuring that at the switch there isn't some other bug it could be....going to trouble a friend to use his and verify.