Wiring

In a nutshell, I removed the 2 plugs from end of 3.0 harness that plug into main dash harness of the 4runner and rewired them on to the end of the 3.4 harness.

 Rewire by removing pins from 3.4 plugs and inserting them into 3.0 plugs. You will also need one of the 3.0 plugs that goes into computer. Because it is possible to remove the pins from the plugs, I only had to splice 6 wires in the entire conversion!

You can download detailed wiring diagram PDF files from Toyota by getting a $10/day unlimited membership to techinfo.toyota.com .

You will need to relocate the battery to the driver's side of the vehicle. You will also need to extend the connection to the main fuse/relay box that went to the positive terminal of the battery.

Because of differences in the wiring of the starter, you will need to run a wire from the starter relay (located in the relay/fuse box under the hood) to the starter solenoid. I cut the end off of the 3.0 wiring harness and also stole a pin with pigtail to plug directly into a plug the relay box. If you have completed the swap and it won't turn over, this is probably what you forgot to do!

Soon after I started driving the truck, I noticed that the battery was not charging. The alternator did not seem to be doing anything which I thought was strange. It turned out that I had plugged in the engine wiring harness to the voltage regulator which was not connected to anything. I removed this plug and used the plug on the driver's side fender that was a part of the original 3.0 harness. This fixed things.

I used the 3.4 wiring boot that covers the hole in the firewall. It required that I modify the metal plate to fit it to the shape of the firewall. I will attach pictures shortly.