I had a similar problem. In my case the problem was intermitent. The dealer replaced the microswitch and it did not fix it. I returned and mentionned that it was still a problem. They look at it and told me that they where not able to reproduced it. So I decided to fix it myself.

If I remember correctly, the current flow from the microswitch to the solenoid and then to the brake switch. In my case, the problem was the brake light switch. The ON resistance of the switch was about 2 Ohm. The solenoid was clicking and sometimes working and sometimes not.

I replaced the switch and it is now working fine. The switch that closed the loop is a dual pole switch, one pole is used for the brake light and the other one to trigger the solenoid when the shift lever is in the park position (the purpose of the microswitch is to only trigger the solenoid when the lever is in the park position). The switch is located near the top of the brake pedal arm. To see it you have to removed the bottom panel.