How To Control Both Fans Using Aux Fan Switch on the C4

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For C4 Corvettes with dual fans, the Aux Fan Sw only controls
the auxiliary fan. The ECM controls only the main fan. When a low
temperature Aux Fan Sw is installed to compliment a low temperature
thermostat only the auxiliary fan comes On at a lower temperature; the
main fan still comes On at the stock setting. This often results in
inadequate air flow to properly cool the radiator in slow moving
Jumper the Aux Fan Sw Grn/Wh lead into the the
Grn/Wh lead comming from the control pin of the main fan relay. This
allows the Aux Fan Sw to turn On the main fan along with the auxiliary
fan. The ECM can still turn On the main fan should the A/C pressure sw
demand it.
– (2) insulation displacement wire splice
– (2) crimp connector plugs to fit the splice
– enough 18-20 Ga stranded jumper wire to reach from the Aux
Fan Sw to the main fan relay (Grn is an appropriate color).
– several
black wire ties
– black plastic electrical tape
1) The Aux Fan Sw is located in the left side of the block
below #1 & #3 spark plugs.
2) On a 1988 Corvette, the main fan relay is
located on the inner rear of the left fender well; here the length of
jumper wire was about 1 ft.
1) Locate the Aux Fan Sw
and the main fan relay and determine the correct jumper wire length.
Verify that the wire colors match those described here and update any
3) Purchase the required materials.
4) Disconnect the
battery lead.
5) Strip the ends of the jumper wire
6) Crimp the two
plugs onto either end of the jumper wire.
1) Pull
some of the Aux Fan Sw Grn/Wh wire out of the wire harness that runs along
the left inner fender well.
2) Carefully crimp a splice connector onto
this wire so that it can be placed back into the harness.
3) Unwrap
the wires comming from the main fan relay to expose a length of the Grn/Wh
control wire.
3) Carefully crimp the other splice connector onto this
4) Dress the jumper wire along the wire harness between the Aux
Fan Sw and the main fan relay.
5) Plug the jumper wire into the two
splice connectors.
6) Wrap each splice with black plastic electrical
7) Open the wire harness, cutting any necessary wire ties and
press the jumper wire and connector(s) into the harness.
8) Close the
harness and secure with wire ties to prior configuration.
Reconnnect the battery lead, start the engine and observe that both fans
come On at the temperature setting of the Aux Fan Sw.
The required mateirals can be purchased from a general electronics
supplier like Radio Shack for $5-$10.

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