Brake light trouble.

[CaptainHook01]

I just picked up a 2008 M1097R1 a week ago. I’m new to hmmwv’s I’ve always wanted one and finally have one. When I was checking everything out my brake lights worked. I took it for a short drive around the neighborhood and was told the brake lights weren’t working. Got it home and the brake lights worked. Had someone follow me and they weren’t working again. All other lights work as they should. What could be the problem with the brake lights?

 

[Coug]

there is a switch down at the pedal area that is notoriously out of adjustment.
When testing at a stop you tend to use a lot of pressure, but often when running/driving it doesn't take as much pressure, so you aren't actually activating the brake light switch.
There is a way to adjust the switch by loosening the mounting bolts for it, or I did a roadside fix with a couple pairs of pliers and just bent the rod from the pedal to the switch.

 

[Thumper580]

I just picked up a 2008 M1097R1 a week ago. I’m new to hmmwv’s I’ve always wanted one and finally have one. When I was checking everything out my brake lights worked. I took it for a short drive around the neighborhood and was told the brake lights weren’t working. Got it home and the brake lights worked. Had someone follow me and they weren’t working again. All other lights work as they should. What could be the problem with the brake lights?

Use a volt ohm meter. Loosen the screws holding the switch.. Set meter to make a beeping noise when the switch is moved(put probe ends in the wires coming out if the switch). Adjust the switch position so that it beeps with the least movement of the brake pedal.......

 

[Mogman]

I just picked up a 2008 M1097R1 a week ago. I’m new to hmmwv’s I’ve always wanted one and finally have one. When I was checking everything out my brake lights worked. I took it for a short drive around the neighborhood and was told the brake lights weren’t working. Got it home and the brake lights worked. Had someone follow me and they weren’t working again. All other lights work as they should. What could be the problem with the brake lights?

Welcome to the forum!!

 

[CaptainHook01]

Welcome to the forum!!

Thank you.

 

[CaptainHook01]

Use a volt ohm meter. Loosen the screws holding the switch.. Set meter to make a beeping noise when the switch is moved(put probe ends in the wires coming out if the switch). Adjust the switch position so that it beeps with the least movement of the brake pedal.......

Where is the switch located?

 

[springer1981]

Where is the switch located?

Under the dash next to and attached to the brake pedal.

In my signature there is a download for all kinds of manuals and pdf files. It includes electrical wiring diagrams etc.

 

[CaptainHook01]

Under the dash next to and attached to the brake pedal.

In my signature there is a download for all kinds of manuals and pdf files. It includes electrical wiring diagrams etc.

Thank you I will check that out.

 

[papakb]

I always thought you could add a diode in the circuit so that the E brake light on the dash would light when you stepped on the service brakes as an indicater that the rear lights were working. I never worked it out but it should be a simple addition to the wireing.

 

[CaptainHook01]

I always thought you could add a diode in the circuit so that the E brake light on the dash would light when you stepped on the service brakes as an indicater that the rear lights were working. I never worked it out but it should be a simple addition to the wireing.

Please let me know if you figure that out. That would be a nice safety.

 

[Mogman]

I always thought you could add a diode in the circuit so that the E brake light on the dash would light when you stepped on the service brakes as an indicater that the rear lights were working. I never worked it out but it should be a simple addition to the wireing.

It would take more than a diode, the brake warning light requires a ground to illuminate, there is no ground available in the service brake circuit it simply passes hot along to the rear lamps.
Besides you would NOT want the light to illuminate when you step on the brakes as the brake warning light will also warn you of an imbalance in the braking system when you step on the brakes as it is also connected to the brake equalizer block, the lamp illuminating when you step on the brakes is a BAD thing!
Also it is a parking brake, totally worthless in an emergency.

 

[Mogman]

This should be considered mandatory reading for anyone with a HMMWV, the description of how the brake warning light works is clearly listed in here.

 

[papakb]

I couldn't agree more with you about reading the -10! New buyers should have to sign off on that before they're allowed to take possession of their truck. As for the brake led, I hadn't considered that it's also a warning for a brake system imbalance but adding another one to the trucks wouldn't be that hard to do,

 

[Mogman]

I couldn't agree more with you about reading the -10! New buyers should have to sign off on that before they're allowed to take possession of their truck. As for the brake led, I hadn't considered that it's also a warning for a brake system imbalance but adding another one to the trucks wouldn't be that hard to do,

Adding another light would be easy just wire it from the cold side of the switch to ground.
This of course should be the second lamp added, the first and one that everyone with a Detroit engine should have is one wired between one of the glow plugs and ground so one can actually see what the glow plugs are doing, now that could also be connected to the brake switch with a couple diodes for a dual purpose warning light.

 

[CaptainHook01]

Ok I found the switch under the dash. How do you adjust it the mounting holes aren’t oblong to allow for adjustment.

 

[Thumper580]

The switch mount is slotted... Use the ohm meter set to beep. Adjust it so it beeps with minimal pedal movement.