456 Radiator Fan Issue

Any help would be great. My oil fan is coming on but the main radiator fan is not. The fuse is good and I am measuring 12.4v at the connector. I have ran a wire between the connectors to make sure it is not a bad connection. When I plug in another 12 volt battery directly to the fan, it comes on just fine.

 

I am not an expert but if the switch is okay and fan itself works this could be the sender unit under the plenum?

 

I had a similar problem with a twin-turbo Callaway Corvette.

The temporary fix (until I had a reason to go deep)
was to mount a switch dedicated to the fan that
could turn on and off supplemental 12v directly
from the battery to the fan.

If this were a more long-term fix, I
might find a convenient
HD gauge wire with a fuse in line......

If you have to go under the intake manifold,
do yourself a favor and get a set of HD hoses
and clamps from Scuderia Rampante,
and install them at the same time.

Think ahead, and get all the under-manifold
problems accounted for ahead of time.....

 

This might sound really newbie but the switch on the bottom should always measure 12v correct? This might be the problem. I was trying to take that power and go directly to the fan to see if it comes on which it doesn't. The oil cooler fan comes on, do they get triggered to come on by the same switch?
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