BMW Coupes and Sedans 1970-1988 Repair Guide
Remove the wire terminal from the thermo-time switch.
Connect a test lamp to a positive terminal and the
terminal of the thermo-time switch.
The lamp should light at coolant temperature below 95°F (35°C).
Leave the test lamp attached to the
terminal and connect a positive jumper wire to terminal
The internal bi-metal control should open after a short time and the light should then go out. If not, replace the thermo-time switch.