Can't get brake warning lamp to work

[tb3]

stock 86 t type but master cylinder has been converted to vacuum brakes.

My brake warning light has not worked since I bought the car. I'm getting 12 volts to the lamp in the instument panel with the ignition in the "run" detent, but its not getting a ground from any of the 4 switches that activate the light. I am completing a closed circuit to the lamp whenever I:
1. activate the e brake
2. grounding the pressure switch on the combination valve
3. turning the ignition to the "lamp test"
4. The other switch that activates the lamp, according to my 87 buick service manual is a switch from the brake master cylinder, but the car has been converted to vacuum brakes, so that switch is out of the loop.

But, still not getting the lamp to come on. (yes the lamp is good)

So ,I'm not getting a ground to chassis/body to complete the circuit for the lamp to light. Is there a common ground that all 4 switches tie into under the dash somewhere? The schematic in my manual just shows them going to ground at each switch. I can't find any unhooked or broken wires under the dash. Anybody have any ideas?

 

[garyk1970]

youve done everything i would recommend....also,the plug on the back of the cluster/ribbon cable are not good or reliable on some cars,especially if the cluster has been removed several times.

heres something to try; set parking brake w/key on and then use an old school test light (instead of grounding it,hook it to positve voltage,this way it will light up when it "sees" ground)and start at back of cluster and follow circut traces,plug,etc.to see where neg. volt. stops

out of curiosity,i checked mine,the brake warning lamp doesnt light up with the ign "test" or park brake either?

also,the combination valve and e-brake ground with its mounting bolts/screws.

 

[tb3]

fixed. Thanks for the reply garyk. I swapped the lamp socket out with another one, the socket was bad (one of the contacts was mashed over to the side, not making contact with the lamp contacts, but was making contact when I stuck the needle from my multimeter into it. I know, a obvious one, I don't claim to be the sharpest pencil in the box. Lamp now works as it should.
Looks like the service manual is wrong, the lamp test is in the "Start" position.
However, you should def. get a light with the ignition on and the park brake is engaged. At least its that way on all three of my turbobuicks.
Which is something else I should have checked before posting.

 

[garyk1970]

good deal,usually its in the smallest of connections where all the probs comes from.

my car had a bad socket on the left turn lamp,i didnt notice the brake lamp not working,i could have checked it too since i had it all taken apart