Auxilliary Battery Locations
Trucks with electrical options EXCEPT the aux battery got a plastic-mounted threaded junction post instead of the relay. Most trucks got nothing (like the one shown).
The Y wire ties into the auxilliary lighting circuit (Y and Bk/Y) at a heavy splice inside the dash harness, OR (early) directly to the battery through a Br fusible link at the starter relay.
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The continuous-duty relay (metal case) mounts at the 2 factory dimples in the firewall, and is triggered by a Wh/Pu wire that taps off the back of the fuse block & passes through its own rubber grommet in the firewall.
The aux battery hot wire (R) runs inside the L fender to the optional aux. battery tray, similar to the '87-96 diesel tray shown here:
This option was not available after '86 because of the EFI air filter's location, except on '87 351ci (carb).
