>It's an 89 Westy Syncro.  The aux battery is hooked up with a SurePower 1315.
>Best regards.

This should work for your 1989, depending on how you wired things up;
If you have a different year, check Bentley wiring diagrams before
proceding.

1) Disconnect battery grounds.

2) Remove the two phillips fuse box screws at the bottom of the
fusebox and carefully lower fuse box.

3) Find the pair of wires that went from the original Relay under
drivers seat to behind the fusebox.

4) If those wires are no longer in use, disconnect them at both ends.
The goal is to use the larger of the wires to BACKFEED power from the
Aux battery up to under the fusebox so we can tap into the circuit
that runs the house lights (and radio in your case) without having to
run any new wires.  You may be able to use the smaller wire,
depending on the load of your lights/radio.

4a) Alternatively, you can run a new (Red is best) wire from the Aux
battery Positive terminal up under the carpet and into the area
behind the fusebox.  It's best to put an in-line FUSE as close to the
battery as possible to eliminate short circuit/fire risks.

5) Now remove the big red multiple connector plug from behind the
fusebox (The B connector on page 97.119).  Put on your reading
glasses.  Find the RED wire in hole marked "12".  Use a poker tool
and or pliers to remove the wire/pin from the large connector.  It
will be somewhat tough to yank it out because of the barbs on the
silver tip but it will come out.

6) Now take the wire coming from your Aux battery positive terminal
and connect it to the B12 wire you just liberated from the Red B
connector.  Plug the B connector back into the fusebox and ensure the
clips click so the other items in the B harness will work.  We are
now feeding that red wire (house lights/radio) that used to be in
slot B12 with the Aux battery instead of the engine battery.

7) Reminder, ensure you added a fuse holder to the wire went up to
under the dash...since we are now bypassing the factory fusebox.
Always best to have the fuse as close to the battery as possible.

8) OPTION, you can also liberate the red wire of B11 in a similar
fashion if you want the dash cig. ligher sockets to run off of the
Aux battery.  See page 97.128 for wiring diagram.

9) Now if you leave the interior lights/radio on for a few days you
will still have engine battery for cranking!

-Paul

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