Once you start installing brighter headlights, and add electrical gear such as two-way radios, ARB compressor, 12v cooler, sump pump, voltage inverter, etc., you start taxing your factory Toyota wiring harness. The easiest mod you can do is increase the amount of current able to travel from the battery to the wiring harness itself.

I have performed this mod to my 1985 pickup, Ray's 1985 4Runner, and Shane's 1992 4Runner. Other years and models will most likely be similar. I have looked at many wiring harnesses at the wreckers, and have observed that this mod will work with EFI-equipped 4x4 pickups and 4Runners from 1985 - 1995, 4-cyl and V6, except diesels.

Only attempt this if you know what you are doing. This mod is performed entirely at your own risk. I am not responsible for any problems arising from your workmanship, your failure to follow directions, or your inexperience or unfamiliarity with electronics.

The steps are as follows:

Remove the negative (-) cable from the battery. Remove the positive (+) cable from the battery.

Remove the cover from the under-hood fuse box. 1989-1995 pickups and 1990-1995 4Runners only: Remove the plastic plate from the bottom of the under-hood fuse panel.

Parallel the existing factory wire from the positive (+) battery connector to the black 80A fusible link: Use at least a 12 gauge wire; the thicker the gauge the better, but if you go much thicker you will not be able to fit the wire into the under-hood fuse box (you'll see what I mean when you have a look at it). Remove the 80A fusible link socket by prying the locking tab out (towards the firewall) with a flat-blade screwdriver, pushing down on the fusible link to remove the socket from the bottom of the fuse panel (do NOT try to remove it by pulling up; it is bolted in place). When the fusible link socket is exposed, measure the length of the stock wire the goes from the metal plate on the fusible-link socket and the positive (+) battery terminal, and cut the new wire to the same length. Attach a ring connector to each end, remembering to slip the two pieces of heat-shrink tubing on before the connectors are attached (there is a proper way to "attach" crimp connectors; read this if you aren't sure). Attach one end to the positive (+) battery connector, and other end to the common-side of the 80A fusible link (the side with the large metal plate). Use a socket on the bolts, not a screwdriver; the screwdriver will just strip it, and besides, they're really tight. The common-side and fused-side bolts have different-sized heads. This quick mod will allow more current to travel to the common-side of the fusible link.

While the fusible-link socket is out, have a look at it. See the unused receptacle? This is used for diesels only, and we can use it for our purposes. You can install a second 80A fusible link in the unused receptacle. I use the original fusible link for the factory equipment, and the second fusible link as the source for my additional electrical accessories, such as the ARB compressor, the comm gear, and the aux lights. You can run a heavy-gauge wire from the fused side of the second fusible-link to a remote fuse panel, or wire up individual fuse-holders to it if you don't have too many connections to attach. Why not just attach all the accessory wires to the battery? Because this way the wiring looks a lot cleaner, and you don't have a big wiring rat's nest at the battery terminals.

Re-install the fusible-link socket into the under-hood fuse box. Push up until you hear the locking tab "click" into place.

Replace the cover of the under-hood fuse box. 1989-1995 pickups and 1990-1995 4Runners only: Replace the plastic plate from the bottom of the under-hood fuse panel.

You should also make sure the ground is good: Run a heavy-gauge wire or braided grounding strap from the firewall to the frame, from the firewall to each inner fender, and from the firewall to the engine block. You may also want to run an additional heavy-gauge wire from the negative (-) terminal on your battery to your ground connection on the passenger-side inner fender; I don't know what the stock wire looks like as my factory setup was destroyed in the previous-owner's accident. I have heavy-gauge cables running from the negative (-) terminal to the passenger-side inner fender, and from the negative (-) terminal to the frame.

Re-attach the positive (+) cable to the battery. Re-attach the negative (-) cable to the battery.

This would probably be a good time to remind you to keep a couple of spare 80A fusible links in your kit, as well as a few of each of the other fuses in the under-hood and under-dash fuse boxes. It also would be a good idea to have spares of the relays that plug into both boxes. Just go to a wrecker and grab one of each; they are cheap, but priceless if you need them on the trail. Make sure you grab the three little bolts when you remove the 80A fusible link; you can use one when you install your second fusible link as above, and you'll have a couple spares for when you drop one into the mud. :)

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