How-to
1985 Ford Bronco Tailgate Window Motor Relay Rewire
The factory wiring powers and grounds the tailgate motor through the dash switch and a long run of thin wire, which eighty5eddie reports causes high resistance and weak operation. This rewire feeds the motor through two single pole double throw relays fed by a thick power wire and a closer chassis ground, leaving the dash switch to do nothing but trigger the relays.
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Step 1
Gather two single pole double throw (SPDT) relays and a heavy power wire, and plan to reuse the existing dash switch wiring. eighty5eddie notes that leaving the dash switch to trigger relays also makes it easy to add further tailgate switches later.
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Step 2
Find the wiring coming out of the tailgate and cut three wires: the two pink wires and the black/white wire. Separate the cut ends so each one can be identified and reached.
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Step 3
Run the heavy power wire from the battery to the driver's side rear by the taillight, and strip the wire ends to be joined. Connect the black/white (BK/W) wire to the heavy power wire, which powers the key switch on the tailgate.
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Step 4
Splice the heavy power wire at the taillight so it carries two wires. Run one of those wires to the 87 post on each relay.
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Step 5
Connect the pink/light brown (PK/LB) wire coming from the tailgate to post 30 of one relay, and the PK/LB wire coming from the dash switch to post 85 of that same relay. Wire the second relay the same way using the pink/light green (P/LG) wire, tailgate side to post 30 and dash switch side to post 85.
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Step 6
Ground the 87a and 86 posts of both relays to the chassis. eighty5eddie stresses that this must be a good ground, because the tailgate motor draws its power through it.
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Step 7
To add more switches later, splice into the same two wires, taking the 'UP' wire from the P/LG wire and the 'DOWN' wire from the PK/LB wire, either at the dash switch or at the relay 85 posts. The album's photos end here, with no reassembly shown.
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