Brake Light Switch

[rustbucketmike]

Brake lights are not working on my '76 FJ40 so I figured I'd have a go at the brake light switch. Here is what it looks like from below:

In the description I have, it says there are two "adjuster nuts". But it sure looks to me like that black nut there is welded onto to the mounting plate. Am I wrong? If I'm right, I guess I have to turn the brass-colored nut below in order to then twist the switch out of the welded nut? How the hell am I going to fit a wrench in there?

Help?!

Thanks.

 

[BeerM3]

It looks like what you have may not be stock and/or the thin nut that snugs against the captured nut is missing? You can unplug it and jumper the plug to quickly isolate if it’s faulty.

Brake Light Switch - OEM - FJ40, FJ45, FJ55 1970-1980

OEM Toyota - Fits FJ40/45/55 - 7/1970 - 8/1980 - If your bulbs are good, this is one of the most common reasons why your brake lights are no longer functioning. *Note: This switch supersedes the original part numbers for Cruisers in this year range. Toyota has consolidated multiple applications...

cruisercorps.com

 

[brian]

Pretty sure the jam nut is on the wrong side.
Should be between the weld nut and the switch.

 

[rustbucketmike]

It looks like what you have may not be stock and/or the thin nut that snugs against the captured nut is missing? You can unplug it and jumper the plug to quickly isolate if it’s faulty.

Brake Light Switch - OEM - FJ40, FJ45, FJ55 1970-1980

OEM Toyota - Fits FJ40/45/55 - 7/1970 - 8/1980 - If your bulbs are good, this is one of the most common reasons why your brake lights are no longer functioning. *Note: This switch supersedes the original part numbers for Cruisers in this year range. Toyota has consolidated multiple applications...

cruisercorps.com

I just got the instrument panel out so testing the switch while it is installed is my next move. FWIW, I managed to get the panel out of the way without unplugging the speedo cable which I was having trouble getting loose.

 

[rustbucketmike]

Pretty sure the jam nut is on the wrong side.
Should be between the weld nut and the switch.

This is what I'm thinking too... Now how do I get that out of there?

 

[ToyotaMatt]

This is what I'm thinking too... Now how do I get that out of there?

you need a new rubber " Cushion " too

 

[rustbucketmike]

One more question, is the switch threaded thru that welded nut? Do I have to spin the switch out? Thanks!

 

[rustbucketmike]

you need a new rubber " Cushion " too

With the nut (correctly installed) on the other side, does the cushion just press directly up against the plate?

 

[ToyotaMatt]

With the nut on the other side, does the cushion just press directly up against the plate?

i have had a bad cushion cause my brake switch to malfunction

 

[brian]

Depress the pedal.
Remove jam nut
Remove switch....yes the entire switch will unthread from the weld nut.
The pedal/cushion depresses a button on the switch. So attention needs paid on the installation of the new switch..so as just the right amount of pressure is applied to the switch from the pedal.

 

[rustbucketmike]

I managed to loosen the wrongly installed jam nut on the brake light switch by cramming a 14mm flare nut wrench into the tiny opening and miraculously budging it just enough to let the switch turn loose. But it seems like the switch is not the source of my trouble. The brake lights are still both not working.

Does it work to test the brakes by leaving the brake switch plugged in and just hanging down? If the button is out then the brake lights should be lit up as long as the ignition is on.... right?

I tested for voltage on the leftmost green wire going into the brake switch (from the fuse box?) and I can see 12+ volts. I test for continuity on the other green wire (to the lights?) and I get nothing. Am I wrong to assume this means I have some wiring problem at the lights in the back?

I opened the rear tail lights and cleaned up the area where the two screws hold the assembly in the bumper. Is the ground for the brake lights at these two screws from the assembly into the bumper? Cleaning it hasn't fixed the problem (neither brake light is working) but I could do a better job getting it cleaned up.

A few of the wires into one of the assemblies appear to have been mashed and damaged. If the wiring was broken into one light would that cause the lights to also not work on the other side?

Thanks for answering my questions. I'm not sure I could even run this truck without the info I get from here.

 

[thebigredrocker]

You are correct the rear light assemblies ground through the mounting screws.

here's a bit of info. you can click on coolerman to go see the rest of the thread

The brake pressure switch's should never see +12V. They are wired to switch GROUND to the Brake warning light.
It works like this: The two pressure switches are wired in parallel with each other and in series with a normally open contact in the brake switch, the brake warning light and on to Fuse A which is hot all the time. The other side of the pressure switches are wired to GROUND.

The pressure switch's are normally CLOSED switches. When you step on the brake you make the contact in the brake switch which completes the path and the warning light turns on for a brief period until enough pressure builds up in the master cylinder front and rear circuits to cause the switches to OPEN thereby turning off the warning light. Any loss of pressure in the brake system will allow the pressure switch to close again lighting the light. Took me forever to get mine to work properly!

Hope that clears up the mystery!

Edit: #40 = E-brake switch, #41 = Brake Warning Light, #42 = brake switch, #44 = pressure switches, #43 = to brake lights
View attachment 123853

This may be the same info

Sounds like a bad switch. If you have the time you can take the switch apart and clean the contacts and check the springs are not broken or out of place. I would just get a new switch. They are cheap. If you don't have a dual master with the brake warning switches then you only need the two green wires. The red wires are part of the brake check circuit on the dual master.

The attached pic shows how this is wired. The pic is confusing as hell but it is accurate.

The numbers are:

40 is the emergency brake switch
41 is the brake warning light on the dash
42 is the brake switch itself
43 is the turn signal switch. (The brake lights go through the turn signal switch.)
44 are the hydraulic pressure switches on the dual master cylinder.

It works like this.

Key OFF: First Fuse A is a switched hot. It's only hot when the key is on. Fuse B is hot all the time. The hydraulic brake pressure switches (44) are closed when the brakes are NOT applied which grounds the red wire on one side of the switch (42). So with the key off and brakes NOT applied the dash (41) light and the brake lights are off. If you press the brakes in this condition you close BOTH switches in the brake switch. This sends power from Fuse B through the brake switch (42) to the turn signal switch (43) and on to the brake lights which will light. Because the key is not on no power is applied to the dash switch so it will not light even if there is a problem.

Key ON: Now Fuse A is hot. If you pull the emergency brake handle, switch 40 will close. Since the hydraulic pressure switches are already closed there is a complete path from ground through the emergency brake switch through the dash light to the fuse and the Brake Warning light lights telling you the Emergency Brake is on.

Now with the Emergency Brake OFF and key ON. If you press the brake in this condition BOTH switches in the brake switch close. Power from Fuse B goes through the brake switch green wires to the turn signal switch and on to the brake lights which will light. If the master cylinder generates enough pressure in the front and rear circuits then the hydraulic pressure switches (44) will OPEN breaking the circuit to ground and the Brake Warning light on the dash will remain OFF. If however the pressure drops in either circuit due to an internal leak in the master cylinder or a leak in the lines pressure will drop and the switch in that circuit will close. This provides a path to ground to the Brake Warning light which lights telling you there has been a drop in pressure and you should check it NOW. It's normal for the light to flicker when you hit the brakes. HTH's!
View attachment 115762

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