Hi, just picked up on this topic out of desperation !
I have a similar problem. GM 500 linked to PM 1 point motors with polarity changing and motor operation via the GM 500. Power is 16 v AC. when the motors are not connected to the GM 500 the relay works fine. When the PM 1 is connected in the point motor works fine but the relay does not. I have bypassed the resistor as suggested but still have the problem with the relay not working.
I'm running out of ideas other than to get a couple more GM 500's and test them in case mine is faulty.
Just wondering if any has any further ideas that I could try
Thanks
Robert