my 84z with l69 is rebuilt, carbed/ headers etc.etc. I have no computers in this car at all, the factory fan is new and it works only when you slide the lever over to a.c. can anyone tell me how to do a simple manual switch installation so I can turn it on manually when needed?

 

First of all look at the passanger side head underneth the Exhaust manifold, between cylinders #6 & #8, (Not the one in the drivers side head it is for the temp guage only). There should be a Temp Fan Switch there.

Trace the wires coming from the fan motor, They should run to a relay, the relay should have a green wire with a white stripe on it. That is the wire that should go to this Switch.

If you do not have this switch it is AcDelco part#D1874D i am pretty sure.
This is a pic of it Fan Temp Switch Get this Sender and Run that Green wire with white stripe on it to that switch. now when The engine gets to about 196 degrees maybe a hotter it will kick the fan on and when it cools down to I think 176 degrees , It goes off.

Now If you want to wire a manual switch inline to this Green wire with white stripe (which is a Ground BTW) Ground a section of wire the other end hook to a Switch in. On the switch out run a wire and tap into that green with wite stripe. When you Flip the switch to complete the circuit the fan will come on.

lease Double Check all Wire Colors before Trying This
And this should only be a temp Soulution. For a more perminate solution check out ******* Total Fan Control Sticky Here for single fan orhere for dual Fans