Using a continuity light - I attached one end to the grounds in the spare tire well and tested each of the five connections at the harness plug. Holding the plug with the 3 wires on top I got continuity at the left most of the top row and right on the bottom row.

Checking continuity from #4 to the harness plug the same two connections had continuity.

This is what I think based on that at the harness:

(1) (3) (5)
(2) (4)

At the pump

(5) (3) (1)
(4) (3)

Sound right?

 

I powered up the pump with my Ohmmeter attached to what I think is 1 and 4. Switch started and stayed open - 0 ohms. I put the unit back into the car and the pump would never shut off - I believe the pressure switch is kaput.

Basically, one switch was stuck closed and one was stuck open.. Oh joy.

Sadness - time for a new switch $$$.

 

I think it is much more likely that the pump isn't pumping properly. If the switch were bad (i.e. motor contact stuck closed) then the pump would start slowing as the pressure built. If the switch didn't stop it then the motor would eventually stall from the pressure, and the fuse would go. (Unless the accumulator blew up first. Be careful, this is serious hydraulic pressure).

As Greg mentioned above and long ago, the most common problem is getting the pump primed. If that's OK- and it pumps fluid with the bleeder open-- then the next problem is the pistons and ***** being able to move, yet seal properly.

You mentioned sandpaper above, to get rid of the varnish. I don't like the sound of that at all. There are no rings on these little tiny pistons-- they rely on tiny and precise clearances to seal without binding. If you scored the pistons or the bores then they are likely done, unfortunately.

Check the prime first. If the pump is in the car then open the bleeder and run the pump-- it should pump fluid out the bleeder. Then close the bleeder, you should hear the pump start to load up and slow down as it builds pressure.

 

The pump makes pressure - I was able to bench bleed the pump. I could see the fluid going through the external filter and draining the reservoir. I test fit the the cylinders and made sure they moved freely. I hear the pump begin to slow down as it builds up pressure. I was very careful cleaning the pistons - not overly aggressive with very fine wet-dry sandpaper. Once assembled I spun the motor to and fro and hear the ball bearings move. Can hear them upon start of the motor. The motor does load up after a few seconds according to my ears.

On my 91 the pump runs for just a few seconds before it shuts off. Not so on the 90.

Kevin

Edit: This whole adventure started with a blown fuse in the spare tire well - So, that would suggest the original issue was a bad pressure switch.

 

New switch still won't shut off. I bled off air and clear fluid comes out. When I say the pump makes pressure I am not sure that is a correct statement. What I do know is the pump will move fluid.

I let the pump run for less than five minutes and the motor did not seem to labor.

No leaks.

Did I not wait long enough? The whole system has been wide open.

I did notice when I removed the previous switch there was a release of pressure and a tiny bit of fluid - the fluid seemed foamy with air in it.

Any guidance is appreciated.