Hi all,
I am new to this forum and have a 1987 420 SEL. Just bought it two months ago in cherry condition. The coolant was below the sensor, but the coolant level warning light was not on, regardless I added about 1 quart of coolant. Just recently the coolant level warning light illuminated, so I assumed the coolant was low again, but it was not. No loss of coolant, yet the light comes on after 1 minute or so. Could it be a bad coolant level sensor, or coolant temp (the water temp gauge is at 90) and is there a test for the sensor?
Thanks for all the help

 

Sounds more than likley it is the level sensor. To check it you have to remove it and use an ohm meter to check continuity while turning the sensor upside down and right side up. Or just unplug it and make the light go away- some 126s had no sensor at all.