1969 Cougar wiring

Having issuers with the brake pressure warning light, will not come on when I turn on the ignition before start. I have brake lights and have changed the bulb. What controls the light? Do I need to replace the 15 amp relay?

Have you checked if the wiring is plugged into the switch? Switch screws into the brake distribution block.

Yes it is a news switch.

The brake warning light is called the “prove out” circuit and is activated when the ignition switch is turned to the START position. Internally the ignition switch’s START position enables a ground circuit to turn on the brake indicator.

Coach Jack

It’s a new ignition switch, could it be just a bad ground?? Faulty switch?

With the key on, pull the plug on the distribution block and short the two leads in the wiring end of the plug and the light should come on. If it does come on then you know the circuit is good and most likely it’s the ign switch. If it does not come on then start tracing out the wiring in the light circuit. The wire (violet) comes from the ign switch to the brake switch back to the plug in the dash (also violet), that is the failure circuit, the ign circuit feeds the dash thru a blk/grn wire to the dash plug, you will have to pull the dash to test the plugs. Do the other warning lights come on when you start? If so it is probably not the switch but the connection in the dash. Good luck!

For the lights to turn on, there has to be power to the bulb and just as important a ground path to complete the circuit. All of the the dash lights (Brake, Oil, Alt and Temp) are all powered via the C post on the ignition switch. The C post provides power in the ON and Start position of the ignition switch.

The Oil, Alt and Temp light are powered in the ON position and illuminate as their respective sending units provide their own grounds.

Although the Brake light is also powered in the ON position, the Brake light does not illuminate in the ON position because their is no ground circuit (assuming that the dual brake warning switch is centered in the master cylinder). The PROVE OUT circuit on the ignition switch are engaged when the ignition switch is in the START position. It is the PROVE OUT circuit that provides a ground to complete the circuit so that the BRAKE dash light lites up.

So with this information, let me address some of your concerns,

  1. The Brake light will not turn on in the ON position, only the START position
  2. The rear brake lights have nothing to do with the brake dash light

As Mistress pointed out, do the other warning lights illuminate when in the ON position? If these do not, then there is a problem with the power lead from the ignition C post to the circuit board.

Assuming the engine warning lights turn on, next test the brake dash light by turning the ignition to ON and ground the contacts on the dual brake warning switch. If you just connect the two, you still wouldn’t complete the ground circuit. If the Brake light now illuminates, then the problem lies between the violet wire from the warning switch to the Prove out connector in the ignition switch or the ignition switch itself.

Coach Jack

Thanks for the info, all the lights work except the brake pressure light on the instrument cluster. I will try some of the suggestions you guys provided.