My central locking system quit working on my 87 300D.
I have searched through many posts, including a very helpful one by Kenhartz back in 2011, but still cant pinpoint the problem.

I have check my x30 box, and dont see any sign of corrosion or any other problem.
Checked fuses-they are fine.

I have verified that the system holds vacuum very well for long period of time.
Following instructions by Jeremy in:
HELP!! 87 300D central lock nightmare! I cant get the doors to lock or unlock at the pump.

I have put 4 different pump from old cars in my car as a test, but I still cant get my central locking system to work. (The locks function manually just fine)

I traced the 3 wires from connector 2(at the pump) to the brainbox for the security alarm. they ohm out just fine.
My security alarm works fine. (I even replaced the brainbox under the passenger footbboard-as a test.)

Can anyone offer any assistance here??

I find it hard to believe that all 5 of the pumps are bad, but it is possible. Can anyone tell me how to bench test the pump??

Thanks for your assistance.