Ford 1980-86 auxiliary battery bracket relay and wiring diagram…

'80-86 Auxilliary Battery
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Ford's instructions for wiring modifications are in this caption:



EOTZ-10732-A left battery tray assembly
EOTZ-10769-A left battery tray support



Not compatible with underhood tool box:



The "Accessory Relay" is a continuous-duty relay, which may LOOK like the starter relay, but is built to tolerate being continuously ON.

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The best relay in the 2020s is the same White-Rodgers that's popular as a glow-plug relay upgrade on diesels.

In the factory wiring, the Wh/Pu wire is hot in RUN only, so the Aux.Batt. gets charged whenever the engine runs, but is isolated from any drain all other times. With the addition of the switch, the operator can choose to jump-start a weak main battery using the aux., but a new 0-4ga cable must be added (bypassing the fusible link & junction stud) to handle that kind of current. He can also choose to disable the aux. battery relay in the ISOLATE position. The AUTO position preserves the factory behavior.

The 5A fuse protects the switch circuit and provides JUMP power to the aux relay.

The 2-color LED (in the Isolator diagram) only works if the key is in RUN. It glows red if the aux battery is weaker than the main, regardless of the isolator switch position (indicating a problem with the aux batt charging). It glows green if the main battery is weaker than the aux (indicating that JUMP is needed). It doesn't glow if both batteries are charged, or if both are dead.



See also:

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Owner caption July 2022 · Photo 0 of 5000