88 5kcstq coolant warning problem (neither sensor!)

[auditude at cox.net]

Hi,

My '88 5kcstq is flashing the coolant warning light.  Problem is, when I disconnect both the expansion tank level sensor and multi-function temp sensor, the warning doesn't go away.

My understanding is that those are the only two sensors that can cause the warning light to come on, and that by disconnecting them the system should default to no signal.  The expansion tank is closed to ground when the tank is low, and the overheat signal is also closed to ground.  So by unplugging both, I should not have the flashing light.

What am I missing?

Thanks,

Ken