Starter solenoid clicking-only has been an uncommon but recurring problem on hot days. I've realized it coincides with the radiator fans being on, & it’s been suggested that relays to the starter solenoid would solve it by providing more current.
However yesterday on a hot day the airconditioning, all instruments & power windows suddenly went out. Engine seemed OK, so I continued to drive, looking for an auto electrician. By the time I found one, the engine was boiling, and of course replacing a 35 amp fuse revealed the problem. Leaves me stunned that the engine cooling fans are on the same fuse as these other items – if it blows, not only do you risk engine damage, but since you have no temp gauge or warning light, you have no idea what’s going on. (If you haven’t thought all this thru properly)
Maybe a relay & separate fuse to the radiator fans would be better & safer than a relay to the starter solenoid.