The Buick harness has a six pin connector.
I have notes saying the top of the connector is Pin F orange wire goes to power accy breaker high current, A on switch itself I believe.
Next is E purple/wht. stripe, goes to defogger grid + output, B on switch I believe.
D = Pink/Bk stripe, ST/BLT fused at 20A for timer (good IGN source will do) and should be C on the switch itself.
C = Black Ground, a good ground anywhere will do, D on switch itself.
B = Gray, +12 lamp lighting connection for Instrument lamp lighting, lights up with lights on, terminal E on the switch.
A No Connection on connector, no place for it on switch.
Here would be the way I would test the switch directly to see if it's right.
Ground pin D on the switch and use a 1A FUSED JUMPER from the battery to pin E of the switch.
IF the little indicator light comes on it it you should be good to go with what I gave you.
The switch is labeled differently than the diagram which is labeled off the factory connector itself which is correct and upside down from what I recall when changing mine out and wondering why it didn't line up with the lettering in the diagram.