Cooling fan switch

[kflynn]

89 CA Turbo Supra likes to heat up in traffic. No leaks in the water pump. WP has no bearing noise and appears to develop pressure and circulate. Thermal clutch was tested (spun freely when engine hot) and replaced. The new unit has 100 freeway miles on it so it should have plenty of its fluid circulated. Water circulates and heat develops on top and boottom of the radiator. Radiator cooling fans will activate when the engagement wire is grounded. Is there a way to test the single wire thermal fan switch?

Thanks for any guidance on this one.