What size fuse does this electric fan wiring diagram call for?

A 20a fuse is shown in the circuit between the switch/power wiring and the fuse box.

Should the fan be wired to the battery or a keyed circuit?

The diagram says to wire it to a keyed circuit; if you wire it to the battery, the fan will keep running after you turn off the motor.

What switch positions does the fan control have?

The switch shown has three positions: manual on, manual off, and auto thermo.

How does the thermostat control the fan?

A temp probe connects to the thermostat, which sends a trigger signal (green wire) to the fan relay; the thermostat itself is fed 12v power.

How is the relay grounded in this diagram?

The diagram doesn't specify; a note says grounding options for the relay were discussed and must be worked out on the installer's end.

Home/ Registry/ Ford/ Bronco/ 1978-1979/ “Truck”/ Photo supermotors.net/registry/media/142145

Electric Fan Thermostat & Relay Wiring Diagram - Manual/Auto Switch, 20A Fuse

Electric cooling fan relay wiring schematic — keyed vs battery 12V source, 20A fuse, manual/auto switch

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Hand-drawn electric fan wiring schematic; same fan/relay/thermostat layout noting keyed-circuit vs direct-battery 12V feed and 20A fuse for fan power.

AI caption August 2004 · Photo 314 of 434

This document is a hand-drawn wiring schematic (uploaded as 'wirethis2.jpg') showing how to wire an electric cooling fan with an adjustable thermostat controller and a manual override switch. The diagram shows an electric fan connected through a relay, with a temperature probe feeding a thermostat unit that provides a 'trigger' signal (green wire) to the relay. The thermostat receives 12v power (red wire). A three-position switch offers 'manual on', 'manual off', and 'auto thermo' modes, allowing the driver to force the fan on, force it off, or let the thermostat control it automatically. Power is routed through a 20a fuse from the fuse box. A note instructs the installer to 'wire it to a keyed circuit,' warning that if wired directly to the battery, the fan will continue to run after the motor is turned off. Another callout notes that grounding options for the relay were discussed separately and must be worked out by the installer. Wire colors depicted include red (power), green (trigger), blue (temp probe/switch), and black (ground). This is a community-shared installation guide rather than a factory document, applicable to electric fan conversions such as on the uploader's 1979 Ford Bronco.

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Frequently asked questions

What size fuse does this electric fan wiring diagram call for?: A 20a fuse is shown in the circuit between the switch/power wiring and the fuse box.
Should the fan be wired to the battery or a keyed circuit?: The diagram says to wire it to a keyed circuit; if you wire it to the battery, the fan will keep running after you turn off the motor.
What switch positions does the fan control have?: The switch shown has three positions: manual on, manual off, and auto thermo.
How does the thermostat control the fan?: A temp probe connects to the thermostat, which sends a trigger signal (green wire) to the fan relay; the thermostat itself is fed 12v power.
How is the relay grounded in this diagram?: The diagram doesn't specify; a note says grounding options for the relay were discussed and must be worked out on the installer's end.