A little different powermaster problem

[QuikBuik]

I went to back out of the driveway today and low & behold, with no warning (or dash light) I had a stiff pedal! After pulling it back in and checking, I noticed the powermaster motor isn't even attempting to come on, but the brake light in the dash isn't on! (I double checked with the parking brake and the dash light does work, and goes right back out when you release the parking brake.) I checked and the 30 amp fuse is ok too.

Could this be the pressure switch tricking the system into thinking it's primed when it's really not, and that's why the dash light isn't coming on? I don't have an ohmeter to do the diagnostics, and I'm at a loss. Help!

 

[BJM]

Apply power to the motor and see if it runs. If it runs, check the switch. You need a wiring diagram or a meter. A decent multimeter is only $20.

 

[QuikBuik]

Thanks for the reply. I did some checking and used this diagram....
http://www.gnttype.org/techarea/images/PwrMstr.gif
....and turned the switch on and put a jumper wire to the "B" terminal on the motor and it started running, which means the motor's ok, but maybe it's not getting power from the ignition like it should be.

But yet the dash light is not indicating any problem which leads me to think it might be the pressure switch? Any ideas?

 

[BJM]

Check the switch's metal body and make sure its a good ground. If not, it won't trigger anything. The motor sounds fine. Did you let it pump long nough to make sure the brakes had boost? From the diagram when the boost is gone the pins on the switch should both be ground but I don't think the diagram is quite right, I think the pressure switch is 2 stage or else it would light everytime the motor ran. Nevertheless, pull the switch connector and ground A and the motor should run, ground B and the brake light should light up. If those both work then it sounds like the switch is bad.

 

[BlackBandit]

Sounds like the switch is working. Just looks like you're not getting ignition power to terminal B on the plug. Unplug the motor, turn on the key, and check terminal B on the plug. I believe there should always be 12 volts there, and then the pressure switch just completes the circuit when it needs the motor to run. Least ways that's the way it looks to me. Luck.

 

[QuikBuik]

Well, I found it. I thought the 30 amp fuse was the only one linked to the powermaster. But my brother brought home a wiring diagram that showed a link to a 5 amp relay fuse right beside the cruise control fuse at the top of the fuse box. Checked it, and it was blown. Replaced it, and the motor came right on. I now have brakes.

This seems pretty shaky to me that with this fuse blown, you have no warning light to tell you that pretty soon youre going to have to leg press the brake pedal to stop.