testing brake light switch (1 Viewer)

[brassos]

Hello,
I have a 72 fj40 with no brake lights or turn signals. It does have good running lights all around. I pulled the brake light switch out and it has 2 red wires and 2 green w/stripes at the white plug end.
The 2 reds read continuity with the plunger depressed or not. I can get no continuity on the green terminals together or when jumped from the red side.
Is this a way to test the switch? I ordered a new one anyway as well as a flasher. These are both original parts.
At the rear of the vehicle the green wire is hot and i made a new harness to run the running lights including the tail lights.
The green yellow and green red are dead. Fuses are all good.
I searched forums and see a few suggestions to just get a new switch. New switches and a flasher will help me narrow down the problem.

 

[Hot Tamale]

man i'm having the exact same problem... when you figure out a solution, could you please PM me and let me know what you did? I don't have a clue when it comes to wiring!!!

 

[tlcruiser66]

Check out this link for a wiring diagram.
http://www.ih8mud.com/tech/fj40_wiring_diagram.pdf
Should explain what the wires are and where they go.

Kevin

 

[tlcruiser66]

Check out this link too for checking switch
https://forum.ih8mud.com/showthread.php?t=127650&highlight=brake+light+switch

 

[Coolerman]

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!

 

[DHracer3]

Id been keen to hear more on this issue as I am having the same problems..

 

[bj40green]

Here is a page from my FSM.
It's a double switch (2 steps) the first step activates the brake lights, when you push harder/deeper on your pedal the break warning system is activated. When you have no oil pressure the warning light will come on. There are also other wiring set ups with this same switch but this one is the most common.


Good luck

Rudi

 

[shortroundj]

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

I know this is an old thread but I'm doing some troubleshooting on my 78 FJ40 and have what may be a numbskull question here. What happens key on, E brake on when I press the brakes. Per this shouldn't the pressure switches still open causing the warning light to go out? My warning light doesn't go off when I take my brake off unless I move the handle a little sideways, but if I don't move the handle and it stays on it will then go off when I hit the brakes, which per this makes sense. I know the wiring on a 78 is a little different but should still be same principal right? Per the diagram in any case when brakes pushed and good pressure light should go out, e brake on or not? Or am I missing something?

 

[Engineer8000]

from Mr. Coolerman's web page, 78 wiring:

 

[shortroundj]

from Mr. Coolerman's web page, 78 wiring:

View attachment 2445118

Thanks for this. It's a great diagram. I think I figured out. My brake light does in fact go off when I step on the brakes with the park brake on, which per this it should.

Now need to figure out why my rear hazards don't work unless I hit the brakes. I think PO rewired them in to the brake line as he changed rear lights to LED so they must be shorting somewhere with the brake switch open.

 

[swixtt]

another switch question. the first section of the switch appears to work fine.... when pedal is initially pressed down i can hear a click of the switch, brake lights come on.... when pressed further i hear the second section of the switch activate and the brake lights go out. returning the pedal to mid-point brake lights come back on until it is further released and the lights go off. somehow the second section of the switch is turning off the brake lights. are there adjustments needed to the switch or dig deeper into the wiring?

 

[shortroundj]

another switch question. the first section of the switch appears to work fine.... when pedal is initially pressed down i can hear a click of the switch, brake lights come on.... when pressed further i hear the second section of the switch activate and the brake lights go out. returning the pedal to mid-point brake lights come back on until it is further released and the lights go off. somehow the second section of the switch is turning off the brake lights. are there adjustments needed to the switch or dig deeper into the wiring?

I could be wrong but I don't think it's a two stage switch. So you could have a bad switch.

 

[Skitz]

another switch question. the first section of the switch appears to work fine.... when pedal is initially pressed down i can hear a click of the switch, brake lights come on.... when pressed further i hear the second section of the switch activate and the brake lights go out. returning the pedal to mid-point brake lights come back on until it is further released and the lights go off. somehow the second section of the switch is turning off the brake lights. are there adjustments needed to the switch or dig deeper into the wiring?

I am having the same issue, did you ever trace the issue or swap the switch out?

Thanks!

 

[swixtt]

I have a used switch on the way.