High Speed Radiator Cooling Fans Problem? 350 SDL-126
 

I have a 1991 350 SDL (126), I'm the original owner.

The high speed electrical cooling fans don't come on when needed. New high speed relay didn't help. High speed fans will come on by bypassing the high speed relay (new relay bad too? It clicks when inserted with motor running). A/C and everything else electrical operating normally.

Would appreciate ideas on what the likely suspects are?

Thank you.