Dual brake warning switch connector

[jp2005]

Does anyone know how to wire in after market low pressure connector off the brake valve into current wiring ? Looked at the wiring diagram and the 1968 F250 has two wires not one. Its 977 and 977a looks like a ground but im not sure. Any help would be great.

[knightfire83]

You can connect both factory wires to to your single connector.

Factory operation:

Wire #1: Goes to the brake warning lamp.
Wire #2: Goes to the ignition switch and is grounded when in the start position.

The two wires connect directly to each other inside the switch. So when the ignition switch is turned to the start position, #2 is grounded. This illuminates the lamp thru the brake warning switch, which indicates the brake warning switch is connected and that the light bulb is not burned out.

Unplug the brake warning switch, turn the ignition to start, and the brake light will not illuminate. This is why there is two wires leading to the switch. It is a safety feature... So by disabling it, you do so at your own risk.

When there is a brake fault and the switch closes, it grounds both wires.

Wiring in a one wire switch will still test the light bulb when in the start position and illuminate the brake warning light when there is a fault. However if the connector to the switch becomes disconnected you will never know without visually inspecting it, leaving the brake warning light inoperative if there is a fault in the braking system. I believe 80's on up GM vehicles are like this, probably most others too.

[flyboy2610]

Thanks for posting this!
I've got the same switch, and had been wondering how to wire it. Now I know!

[jp2005]

You can connect both factory wires to to your single connector.

Factory operation:

Wire #1: Goes to the brake warning lamp.
Wire #2: Goes to the ignition switch and is grounded when in the start position.

The two wires connect directly to each other inside the switch. So when the ignition switch is turned to the start position, #2 is grounded. This illuminates the lamp thru the brake warning switch, which indicates the brake warning switch is connected and that the light bulb is not burned out.

Unplug the brake warning switch, turn the ignition to start, and the brake light will not illuminate. This is why there is two wires leading to the switch. It is a safety feature... So by disabling it, you do so at your own risk.

When there is a brake fault and the switch closes, it grounds both wires.

Wiring in a one wire switch will still test the light bulb when in the start position and illuminate the brake warning light when there is a fault. However if the connector to the switch becomes disconnected you will never know without visually inspecting it, leaving the brake warning light inoperative if there is a fault in the braking system. I believe 80's on up GM vehicles are like this, probably most others too.

Thank you very much for the information! I sure do love this website!

[jp2005]

So I connected everything like in the diagram, but how do I know its working. Do I disconnect the switch and turn to start position? Right now the bulb doesn't light up when I turn to start position. Its a new bulb also

[Nitekruizer]

You can connect both factory wires to to your single connector.

Factory operation:

Wire #1: Goes to the brake warning lamp.
Wire #2: Goes to the ignition switch and is grounded when in the start position.

The two wires connect directly to each other inside the switch. So when the ignition switch is turned to the start position, #2 is grounded. This illuminates the lamp thru the brake warning switch, which indicates the brake warning switch is connected and that the light bulb is not burned out.

Unplug the brake warning switch, turn the ignition to start, and the brake light will not illuminate. This is why there is two wires leading to the switch. It is a safety feature... So by disabling it, you do so at your own risk.

When there is a brake fault and the switch closes, it grounds both wires.

Wiring in a one wire switch will still test the light bulb when in the start position and illuminate the brake warning light when there is a fault. However if the connector to the switch becomes disconnected you will never know without visually inspecting it, leaving the brake warning light inoperative if there is a fault in the braking system. I believe 80's on up GM vehicles are like this, probably most others too.

Thanks for the post, the diagram and the explaination. Now it makes sense. I always wodered why it appeared that they had deliberately shorted out the brake warning switch. It's not shorted after all.

[knightfire83]

So I connected everything like in the diagram, but how do I know its working. Do I disconnect the switch and turn to start position? Right now the bulb doesn't light up when I turn to start position. Its a new bulb also

It should illuminate when the ignition switch is turned to start.
You can also disconnect the brake connector and ground the terminal and the lamp will light up. If not suspect the bulb (new or not) and the positive side wiring of the circuit.

An Ohm / volt meter would help with diagnosing problems:
Test one: Remove the light bulb and check for continuity between the light bulb contacts. (lamp good?)
Test two: Find 12volts at the lamp socket when the ignition switch is in the run position. (circuit receiving power?)
Test three: Ground the brake terminal at the valve and check for continuity between the lamp socket and ground. (broken or incorrect wires hooked up?)
Test four: Check for continuity between the brake terminal and the lamp socket. (broken or incorrect wires hooked up?)
Test five: Disconnect the start wire at the starter solenoid (' i ' terminal) then go test the lamp socket for a ground when the ignition switch is turned to start. (bad ignition switch or ground there of)

[jp2005]

So I connected everything like in the diagram, but how do I know its working. Do I disconnect the switch and turn to start position? Right now the bulb doesn't light up when I turn to start position. Its a new bulb also

It should illuminate when the ignition switch is turned to start.
You can also disconnect the brake connector and ground the terminal and the lamp will light up. If not suspect the bulb (new or not) and the positive side wiring of the circuit.

An Ohm / volt meter would help with diagnosing problems:
Test one: Remove the light bulb and check for continuity between the light bulb contacts. (lamp good?)
Test two: Find 12volts at the lamp socket when the ignition switch is in the run position. (circuit receiving power?)
Test three: Ground the brake terminal at the valve and check for continuity between the lamp socket and ground. (broken or incorrect wires hooked up?)
Test four: Check for continuity between the brake terminal and the lamp socket. (broken or incorrect wires hooked up?)
Test five: Disconnect the start wire at the starter solenoid (' i ' terminal) then go test the lamp socket for a ground when the ignition switch is turned to start. (bad ignition switch or ground there of)

Thanks for the reply!

Ill try this troubleshooting this weekend and let you know.

[jp2005]

So I have the wiring hook up like the diagram now after I found my hot wire when in run. I was looking at your diagram and the switch plug has two wires. But the new connector plug only has one so it not going to ground it self out on the outside of the connector. I got the bulb to light up but it stays on when engine running. The way I wired now it

Light doesn't come on this at all on start
Brake connector to bulb
Brake connector to ground wire on start purple wire off ignition switch
Bulb to hot wire off ignition

Light stays on this way when engine runs
Brake connector to bulb ground
Brake connector to ground wire on start red/ blue wire off ignition switch
Bulb to hot wire off ignition

Thank you for your help on this

[knightfire83]

So I have the wiring hook up like the diagram now after I found my hot wire when in run. I was looking at your diagram and the switch plug has two wires. But the new connector plug only has one so it not going to ground it self out on the outside of the connector. I got the bulb to light up but it stays on when engine running. The way I wired now it

The brake switch only grounds both of it's connections when there is a brake fault. It grounds one wire leading to the brake lamp and it grounds the wire leading to the ignition switch when in start. When it grounds the ignition switch wire it doesn't do anything since that wire is also a ground fed from the ignition switch. That wire is only effects this system when turned to start, providing a ground to electrically bypass the brake switch and get the brake warning lamp to light up for testing.

Anyways, if your light is on constantly when running, you have a brake fault. You will need to repair that and re-center your brake distribution valve to get the light to go out. Since you are having troubles wiring this up, you can double check the system. The way to make sure the illuminated lamp is correct would be to check for ground at the brake switch connection. If there's ground the switch has tripped and you have a brake fault. No ground and the light is still on= time to reexamine your wiring connections.

[jp2005]

The brake switch only grounds both of it's connections when there is a brake fault. It grounds one wire leading to the brake lamp and it grounds the wire leading to the ignition switch when in start. When it grounds the ignition switch wire it doesn't do anything since that wire is also a ground fed from the ignition switch. That wire is only effects this system when turned to start, providing a ground to electrically bypass the brake switch and get the brake warning lamp to light up for testing.

Anyways, if your light is on constantly when running, you have a brake fault. You will need to repair that and re-center your brake distribution valve to get the light to go out. Since you are having troubles wiring this up, you can double check the system. The way to make sure the illuminated lamp is correct would be to check for ground at the brake switch connection. If there's ground the switch has tripped and you have a brake fault. No ground and the light is still on= time to reexamine your wiring connections.[/quote]


Just a follow up, I rewired the system and the light doesn't come on when I have the ignition to start. I'm at loss with this man, can you just stop over my place and help me out. I have beer!!!!!!!

[GregoYatzee]

Never found any short til I replaced the wire from alternator battery terminal. This led me to the dash. Then to the light wiring. I unplugged lighting at inside firewall and short was gone from entire dash area. Started tracing outside... First, the “dual brake warning switch” tests continuity to ground, both wires. Not sure where to go with this. Left unplugged for remainder of testing. Tested every light bulb, shorted... Wiring feeding bulbs, good. Bright and dim terminals on headlight bulbs had continuity, turn marker tested continuity between two wires, rear lights...same. My next planned step will be to disconnect all lights and connect everything else and see what happens...

After reading this thread, http://www.fordification.com/forum/view ... hp?t=68376 I will just leave switch unplugged for testing. I'll worry about warning indicators after I get the thing working. I am trying so hard not to give up on this truck. I really appreciate the help you guys have given.

[GregoYatzee]

Oops, posted to wrong thread...