I had a problem yesterday on a long flight from Portland OR to Gallatin MO.
My gear pump light came on and stayed on. I thought I might have a leak but
didn't know. I pulled the LG c/b and continued the flight at 17.5 and a
fairly slow IAS in case the gear was sagging.

When I got to Cameron MO the gear lowered normally and the pump shut off, so
landing was uneventful.

There was no leak.

I'm guessing it's the gear up pressure switch.

What else could it be?

Is there a way to prove whether or not it's the pressure switch before I
order one?

Bill,

 

I take it you have not tried gear retraction again?

 

As you point out, it could be that the pressure switch is faulty or the system is low (not out) on fluid.  If you have the same problem on the way home, you can occasionally reset the motor (and relay) breaker(s) and pump up the wheels if there is enough fluid.

 

Did you also pull the relay breaker while the motor breaker was pulled?  If the system was wired as depicted by Lancair, the relay would remain selected and failure to remove power can cause the up relay to also fail, possibly sticking in the picked state or just as likely to stick in the open state after being over heated and then cooled while not selected.  Remember that there is no cockpit indication that the relay has been selected once the motor breaker has been pulled since a tap on the motor power relay contactor provides the power to the indicator light ("I" terminal on the relay).

 

Here's the old Lancair diagram from the POH that you could have aboard the aircraft: