Powermaster problem scratching my head

[Oakmtnbody]

Just bought a 14k mile 1987 GN and it's in great condition with the only issues being bumper fillers, no problems and the PM brake cyl. Here's the problem, keys not in car but every few minutes you can here the PM electric motor click on and run for like a half second. Get in the car and mash the brake pedal and the motor runs, no keys in the car. The guy had put in a new gray switch but I don't know where it came from, accumulator looks original Oem. Has a small leak from reservoir or rubber hose but very small. How is this PM getting power with the switch off and what makes it click on every few minutes. Any help or suggestions would be greatly appreciated. Thanks in advance.

 

[TurboDave]

There's obviously some kind of wiring errors to allow it to run with key off. When you remove the key, the ignition is off, right?

Posted to TurboBuick.com from my RAZR MAXX HD

 

[Oakmtnbody]

There's obviously some kind of wiring errors to allow it to run with key off. When you remove the key, the ignition is off, right?

Posted to TurboBuick.com from my RAZR MAXX HD

Correct keys are removed Mormon the car and ignition is off

 

[BEATAV8]

see any evidence that somebody might have been messing with the wiring harness under the hood? Any questionable modifications?

 

[Oakmtnbody]

Correct keys are removed Mormon the car and ignition is off

With the ignition off and keys removed I have power on the harness that goes to the grey switch, I show power on the black wire and the brown/white stripe wire and no power on the yellow.

 

[BEATAV8]

I think there's a wiring diagram over at www.gnttype.org

 

[Oakmtnbody]

With the ignition off and keys removed I have power on the harness that goes to the grey switch, I show power on the black wire and the brown/white stripe wire and no power on the yellow.

Just checked the harness on my '86 T-type which is also original and I show power on the same wires with the ignition off. As soon as I plug the harness back in the grey switch on the 87 the motor runs for a half second. Bad switch maybe?

 

[BEATAV8]

here ya go

http://www.gnttype.org/techarea/images/PwrMstr.gif

 

[Oakmtnbody]

thanks for the help guys

 

[TurboDave]

As you can see by the wiring diagram the only way for PM motor to get power is with ignition turned on. So..... I'd have to guess that there is either a faulty ignition switch, or some unauthorized wiring changes made to the car.
As for the PM running as it does, there are two suspects that could cause that. Either a bad accumulator or bad check valve. The check valve is a bit difficult to change for the average PM novice, but the easiest (but not cheap) alternative is to replace the accumulator. The new ones that our vendors sell have proven to be VERY robust and are lasting a quite a good while. It sounds like that would be your first option.

Then, you really HAVE to dig into this power problem!!!! There is NOT supposed to be any power to the system with the ignition turned off.

Here's a quick check you can do if you have a voltmeter handy. Check any of the power points on the fuse panel labeled IGN, with the key off. They should have NO power to them.

 

[TurboDave]

Correct keys are removed Mormon the car and ignition is off

Correct the keys are removed "what?"

 

[Oakmtnbody]

As you can see by the wiring diagram the only way for PM motor to get power is with ignition turned on. So..... I'd have to guess that there is either a faulty ignition switch, or some unauthorized wiring changes made to the car.
As for the PM running as it does, there are two suspects that could cause that. Either a bad accumulator or bad check valve. The check valve is a bit difficult to change for the average PM novice, but the easiest (but not cheap) alternative is to replace the accumulator. The new ones that our vendors sell have proven to be VERY robust and are lasting a quite a good while. It sounds like that would be your first option.

Then, you really HAVE to dig into this power problem!!!! There is NOT supposed to be any power to the system with the ignition turned off.

Here's a quick check you can do if you have a voltmeter handy. Check any of the power points on the fuse panel labeled IGN, with the key off. They should have NO power to them.

I'll check that TD this morning but what's weird is the 86 t has power to the gray switch w/ign off and it does not run when you press the pedal and I have no issues with the PM on it. I'm going to test the 87 like you said and then put the 86 side by side and check each wire with power on and off with my Power Pro. Since I may have a bad Accumilator, master cyl leak and maybe a bad switch I may be better off with a Kirban Reman unit.

 

[aminga]

FWIW the running every 30 seconds sounds like an internal leak. Usually one of the o-rings that seperates the booster section from the master cylinder

But first priority is correcting the wiring.

 

[TurboDave]

Let's try and narrow the problem down a little better before you go crazy and buy a whole unit.

Posted to TurboBuick.com from my RAZR MAXX HD

 

[BEATAV8]

Karp's power brake service sells master cylinder seal kits that will take care of freshening up the master cylinder itself. That will stop any internal leakage.

 

[TurboDave]

With the ignition off and keys removed I have power on the harness that goes to the grey switch, I show power on the black wire and the brown/white stripe wire and no power on the yellow.

I don't understand how you're seeing 12v on the black wire, that's ground. How are you grounding your volt meter when measuring the wires?????
What you're seeing as brown/white is actualy Tan/white but it's probably dirty, and I think what you're seeing as yellow was at one time the white wire.

According to the wiring diagram, the ignition switch provides a ground in run(on), bulb test/start. It provides the ground to the Tan/White wires one of which goes to pin B on the pressure switch which will close below 400psi and provide that ground signal to the motor to make it run. On pin B (Brown) of the motor is 12v in Run only(key on).
Pin A of the motor is the Black wire which is ground, and the other side of the motor windings gets it's 12v on the Orange wire on pin C which is hot in Run(key on).