[DeTomaso] Fan Relay

[Larry Finch]

Mike,

Personally, I think the time has come for you to convert to a modern 4-pin relay, which you can pick up all day for $10-$15 apiece. 
 
A relay has an electromagnetic coil that opens and closes LINE/LOAD electrical contacts.

The 4-pin relays are usually numbered: 85-negative (ground) relay coil input, 86-positive relay coil input, 87-positive relay output(LOAD),  30-positive relay input(LINE). 

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85 and 86 = relay COIL negative and positive power inputs. 
30 and 87 =  relay input (LINE) and output ( LOAD). 

Note there are two positive inputs on the 4-pin relay: 30 and 86 

A 3-pin OEM relay has just one positive input that splits ....internally.... and provides the positive for the relay input(30) AND the relay coil input(86). Look at SOBill?s Panteraplace diagram and note how the ?P? wire lands on two points. 

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The two remaining pins are the negative ground coil input - supplied through the radiator temp sensor - and positive relay output that supplies the fan motor. 

To convert to a 4-pin relay you will retain the original three relay wires and connectors AND add one new wire with a connector spliced into one of the three wires.

First, tap into the ?P? wire with 4-6 inches of 14-18 wire and a female connector. Connect the new wire to terminal 86 and the larger OEM wire connector to terminal 30. This split isn?t rocket science but it should be done in a workmanlike manner that will involve solder and shrink tube, not a crimp-on wire tap. 

Terminal 85 wire is the wire from the radiator temp sensor. 

Terminal 87 wire is the wire that feeds the fan motor.
 
And now you have a modern 4-pin relay connected to the three OEM wires. 

Clear as mud?  ;-)

Larry 

Sent from me using a magic, handheld electronic gizmo.