‘Brake’ warning light question

[Donmcdazzle]

Hi all,

Have searched and can’t seem to find an answer. My 1978 FJ40 ‘Brake’ warning light is not wired up and doesn’t work, however the back of it looks different to the ‘Park Brake’ warning light (which does work).

My question is; should the back of these look the same? And if so, where do you get the right bulb?

 

[thebigredrocker]

Pretty sure it’s a 74 wedge base bulb. If you want to switch it to LED. Try 74-RHP

For more LED bulb info find Trollhole’s thread in the 40 forum. List is updated on next to last page.

Here’s how I find it

Good info on how it works

As I said before, this is the diagram of my '78 BJ40.
Yes it is a funny set up but it works. I asked myself the question, why did Toyota merge 2 systems into 1 brake light?
Why not 2 seperate circuits with a light bulb each?
It took me an hour to figure out the double function of the pedal switch. Let me try to explain.
Situation: engine off, key on.
Pull the parking brake, light comes on. Light has ground via the 2 pressure switches which are normally closed.
Now step on the pedal, light goes out. Because the pressure switches open up and disconnect to ground. This is also a check function to see if your brake system works okay. If you step on the pedal and the light stays on it means trouble under the hood.
Start engine, light is on. Release the parking brake, light goes out. Step on the pedal. Light stays out. So far so good.
Now you have a oil leak or no oil situation. Here is the trick:
When you step on the pedal the rear brake lights goes on via the A-A' section of the switch. But you have a leak so the pedal goes deeper. Now the B-B' section takes over the parking brake switch to keep the circuit going. So the power route is now: fuse - light - B-B' section - pressure switch(es) and because of the leak or no oil the pressure switch stays closed so the light comes on.
This is how it works in my BJ. I know that there are different configurations with oil sensors in the lids, 2 light bulbs and more funny set-ups. I think that this is the most common configuartion for the late 70's series.

Rudi

That light indicates that:
A. The parking brake is pulled.
B. There is no pressure in your master brake cylinder when you apply the brakes.
C. It also has a "check" function. When the parking brake is pulled and you hit the brakes the light should go out.
Here is the diagram
View attachment 1001836

Rudi

That circuit is a bit complicated. There are 2 circuits but one indicator light. Both circuits are connected to the brake/stop switch.
1. The parking brake is hooked up to the B B' section
2. The pressure sensors are hooked up to the A A' section.
With the key in the "on" position the light should be on when the brake is pulled and goes off when the brake is released or when you step on the brake pedal indicating that there is pressure build up in the MC. If the light doesn't go off it means you have a problem with the MC. Low fluid or a leak in one of the circuits.
View attachment 1081909
The adjustment of the brake switch (Warning + Stop light Switch) is essential for good working for both circuits.
Get your brakes in good working order before you start chasing problems.

Rudi