There is a relay that provides the step up voltage in the fuse box. You will have to unscrew the cover and lift it off because the relay is located under it. It is the one closest to the fender and I believe has 4 plugs attatched to it. If I remember correctly the plug for the fans are in the "D" location, to verify look at the wires for the fan and check them at the relay. If I was at my shop I could give you the exact colors.

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'93 300E 3.2
'05 GMC Yukon XL 4x4
'05 Polaris SP500 H.O. LE