Good afternoon! I have searched here and online and have not found anything on this. Even had two other people look at it and can’t figure it out. I have put a Tundra master cylinder on my 1973 FJ40 for my disc brakes. It has a plunger type warning light switch in the cap, not a pressure switch like the OEM. Is there any way to wire it to the existing master cylinder? Or is there a way to bypass? As of now when I step on the break the warning light illuminate. I believe this is because it is not sensing any pressure in my master cylinder. The only wire that I have connected in the engine is a green wire to ground. Thank you for your time.
How should I wire a bigger master cylinder for a parking brake dash light
- Thread starter 1lukeduke
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Engineer8000
SILVER Star
This is how the 73 is wired, 41 is brake warning light, 40 is parking brake switch, 44 is pressure switches, 42 is the brake light switch. The wire colors may be different for you. The parking brake wires are GW in my 73.
When parked, no brake pressure, PS are closed, brake switch is open, no light. Light comes on when parking brake is set.
When pressing on the brake, the pressure switch will open before the light comes on if there is adequate hydraulic pressure. If either circuit has low pressure, the warning light comes on when pressing the brake.
Any path to ground on the GW side of the warning lamp (41) makes it come on.
This is for an 82 with the level float. It is wired in parallel with the parking brake switch. When either of the parking switch or float level switch are closed, the warning light comes on. The diode shown runs over to the alternator so if it fails, it will also pick up the brake warning light. This is how my 73 is wired up.
modified 73 circuit.
The brake light switch contacts are normally closed (shelf state) held open by the brake pedal arm until braking.
When parked, no brake pressure, PS are closed, brake switch is open, no light. Light comes on when parking brake is set.
When pressing on the brake, the pressure switch will open before the light comes on if there is adequate hydraulic pressure. If either circuit has low pressure, the warning light comes on when pressing the brake.
Any path to ground on the GW side of the warning lamp (41) makes it come on.
This is for an 82 with the level float. It is wired in parallel with the parking brake switch. When either of the parking switch or float level switch are closed, the warning light comes on. The diode shown runs over to the alternator so if it fails, it will also pick up the brake warning light. This is how my 73 is wired up.
modified 73 circuit.
The brake light switch contacts are normally closed (shelf state) held open by the brake pedal arm until braking.
- Thread starter
- #3
Perfect! Thank you so much!!!
Engineer8000
SILVER Star
Sure, use the same gauge wire as existing or bigger to ensure coordination with the fuse.
Engineer8000
SILVER Star
Looking at the tundra wiring, it looks like the level switch feeds into the traction ECU. I am not familiar with those caps, be sure it is capable of carrying the current required to light the bulb.
- Thread starter
- #6
Awesome, will do!
Might not be a bad idea to switch that out for an LED so the current draw is minimal
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- Thread starter
- #8
I have. It’s nice and bright!!!