Parking Brake Light Flickering/Dim

by sportster_restorer Thu Mar 01, 2018 7:10 pm

When I step on the brakes on my 74 Laguna, most times the parking brake light comes on dimly and stays on. When I apply the parking brake, it comes on bright. Releasing the parking brake may return it to a dim state, sometimes the light goes out completely. Doesn't seem to be much rhyme or reason.

I checked a wiring diagram and there seems to be a Low Brake Switch with a tan wire coming from it to the dash lights.

I did read the factory owners manual and it said something about the parking brake light may come on if there's some kind of problem with the brakes. I've got a new master cylinder, plenty of vacuum at idle for the booster, and the car stops straight and quickly with a nice firm pedal. Doesn't seem to be any problem with the brakes.

I checked my 75 parts car and thought maybe there was some kind of switch connected to the proportioning valve. Couldn't find anything. I actually checked the whole brake line system as the engine is gone from the parts car so its pretty easy to see everything. Couldn't find anything like a low brake switch.

I thought maybe there's a problem with the parking brake switch. When I pressed the brake pedal and this dim parking brake light came on again, I disconnected the wire going to the parking brake switch. The parking brake like stayed dim, disconnecting the wire to the parking brake switch didn't do anything at all!

So I'm kinda stumped, particularly with the braking system working so well.

by Mcarlo77 Thu Mar 01, 2018 7:26 pm

To shed some light on this, the dash light will illuminate with the parking brake applied OR if the piston inside the proportion valve is off-center. The switch for the dash light on the prop valve is located at center top of the valve. It makes sense that the dash light comes on brightly when parking brake is applied...as it should. I'd focus on the prop valve switch...or, the piston inside needing to be centered. I'd remove the switch (not to worry, you won't introduce air into the lines) and see if the light goes out (which it should). Then, depress the plunger on the bottom against a ground and see if the light illuminates. If both tests check out, it's most likely the piston being a little off-center causing the plunger to be depressed. Even slightly depressed make cause it to flicker. Report back with your results and we'll go from there.

by sportster_restorer Thu Mar 01, 2018 7:49 pm

When I looked at the prop valve on my 75 parts car, there's no wire going to anything on the prop valve. Is there something different between a 74 and 75?

I did look down at the prop valve (located on the frame down waay below the booster on my 74), and didn't see any wire.

I follow what you're saying, like if the rear brakes wear down, and the prop valve is no longer centered, it may trigger a switch. But where the heck is the switch?

by Mcarlo77 Thu Mar 01, 2018 8:13 pm

All original style prop valves on '73-'77 had them. There would have been a single wire plug that pushed onto the post of the switch shown. Here are pics of the new valve with new switch I installed on my '75 Laguna...and, the old, original one:

Parking Brake Light Flickering/Dim Propva11

Parking Brake Light Flickering/Dim Propva11

Parking Brake Light Flickering/Dim Propva10

If someone has replaced your valve with something other than this style, I'm afraid I can't be of much help.

by pila Thu Mar 01, 2018 8:57 pm

If the wire isn't on your switch, maybe it's adrift, and it's grounding on something. See if you can locate it. It's a tan wire..

by Mcarlo77 Thu Mar 01, 2018 9:08 pm

Yeah...that's the only thing I can think of that could be causing the dim light. Not having a wire on the switch in and of itself wouldn't cause the dash light to illuminate.

by thatfnthing Fri Mar 02, 2018 10:07 am

I agree with the above. If it's intermittent, I'm thinking a loose/broken wire or a short somewhere. Since there is always 12v + on the other side of the light, the tan wire to the brake switch IS the actual ground. If it touches a chassis ground anywhere along it's length, the juice flows and the lamp lights. Same with the wire that runs to the e-brake pedal. If either gets grounded, the light comes on.

So since that circuit is always potentially hot, I'd look for a place along those two wires where the insulation has worn and the bare wire contacts metal intermittently.

by Sponsored content

Parking Brake Light Flickering/Dim

Parking Brake Light Flickering/Dim

Re: Parking Brake Light Flickering/Dim

Re: Parking Brake Light Flickering/Dim

Re: Parking Brake Light Flickering/Dim

Re: Parking Brake Light Flickering/Dim

Re: Parking Brake Light Flickering/Dim

Re: Parking Brake Light Flickering/Dim

Re: Parking Brake Light Flickering/Dim