1985 548d parking brake pressure switch question

[CuddleBugFirewood]

I have been working on my skidder replacing brushes in the starter, working on the lighting, rebuilding some leaky hydraulic valves, and going through the wiring....fun stuff.  My problem is the parking brake light/buzzer was not working.  I would like to have it working as it would probably help remind me the parking brake is on before I try to drive away instead of that annoying grinding/straining sound.  You know that can't be good on the brakes, differentials, or transmission. 

Well the pressure switch is missing one of the contacts.  It looks like a stick ran into it as some point long ago, and then someone thought they would cut the wires to the buzzer instead of unscrewing the contact :.  So I thought no problem on the pressure switch, I'll look it up in the parts manual online and order one from John Deere....$175.00!!  I ran into this before with my prentice knuckleboom loader and was able to find a part for 1/3 to 1/2 price by doing a little research...unfortunately this time the only part number I have is a john deere number and that does not match up with any manufacturer numbers on their pressure switches.  I also tried shaffer enterprises in wolf lake and no luck... all out of brake valves and they usually leave the sensors on them. 

So my question is threefold...
1. does anyone know what pressure the switch operates at 500psi?   2500 psi? 
2. what about the circuit open or closed.  I am thinking open (no energy) when the park brake is off and closed (energized) when the park brake is on? 
3. or has anyone bought an pressure switch not from john deere that worked?
 
I have looked through my tech manual and all it says is that the high pressure goes from the park brake valve to the brakes (the pressure switch sits adjacent/inline with this hose I believe), but it doesn't say anything about the pressure switch and what pressure it operates at.  It does talk about energizing the relays when the park brake is on.  The buzzer is turned on by controlling the ground side of the buzzer circuit.  The way I understand it, the light should come on when the park brake is on and the skidder in neutral (energize relay #1), and the light will stay on and the buzzer will sound if I move the skidder into gear while the park brake is engaged (energize relay #2). 

Am I thinking about this right?   Thanks for the help. 

[UN Hooker]

Maybe just screw in a pressure gauge (at least 3K) where the switch goes and apply the brake and see what the gauge reads. You might find a Hobbs switch that will work.
    UN

[CuddleBugFirewood]

I did check the pressure (with engine running 1000 psi, with engine off 500psi).  I was unable to find an aftermarket part even after buying john deeres part and writing the part numbers and manufacture down.  I believe the john deere switch activates around 300 psi and can withstand operating pressures up to around 1500 psi according to the manufactures specs.  I wanted to be able to buy after market next time a stick took it out or it quit working.

Buzzer and warning light now work  ;)  I also added/changed the lights around, added a fuse box to handle the lights. and cleaned up the wiring a little bit.  When I have time some day, I would like to route all the wiring through the new fuse box, but it will have to wait...got some timber to cut.