Today I’ve sort of concluded that the light switch is the most probable cause. Perform the steps proposed by Bill. Based on the results I wasn’t sure which is the culprit. So I removed the dimmer switch and connected the power in line to the dimmer to each of the dimmer output wires (independently of course.) Applying power to high beam wire or to the low beam wire caused the thermal switch to open and remove power to circuit. So I’ve decided to replace the light switch. The switch never failed in the first detent for the Parking lights. Assessing the old switch operation I feel that the switch’s shaft is hard to move through its full range.
I’ll report back once I order and install the new switch.
