Hi all,
I am in the final stages of finishing a 4wd and manual swap on my 2002 4Runner, using a 1995 Tacoma as a parts vehicle. I also used the ECU from a 2003 manual Tacoma, because it works with the electronic throttle of the 02 4Runner and the r150f manual transmission. All the mechanical work is done, but I’m struggling with the wiring. As it stands now, I have no crank and no start. The dashboard shows the door open light, but no turn signal, check engine, or odometer readout. The wipers work, the radio sometimes works, and the turn signals themselves work but don’t show on the dash. I’m going to explain in detail what I’ve done with the wiring, and what I think might be wrong, and if any electrical experts out there can point me in the right direction it would be greatly appreciated.
WHAT I DID
The circuits I’m adding to the 4Runner were pulled from the wiring harness of the 95 Tacoma. There are 2 circuits, one that controls the 4wd and one that connects to the clutch for starting. I’ll cover the 4wd circuit first. There are 2 vacuum solenoids that control the front differential. These are grounded, and then connect to the ADD/Transmission Relay. This relay goes to a junction box, which then connects to power, the ECU, and the 4wd position sensor and ADD indicator, which light up the 4wd light. Included is the wiring diagram for the 95, and the 2004 tacoma which should be the same as the 2003 that the ECU is from, as well as a basic drawing
of how the circuit is now.
CURRENT CIRCUIT
20210324-144655-1 — ImgBB
04 TACOMA
4-WD-wo24-04-tacoma1024-1 — ImgBB
4-WD-wo24-04-tacoma1024-2 — ImgBB
95 TACOMA
4wd-wo24-95-tacoma1024-1 — ImgBB
I don’t think this circuit is to blame for the starting issue. I realized while writing this post that the wiring for the system is more different than I expected between the 95 and the 04, so even though I wired the system to the right pin on the ECU, I may need to change it more. However, I don't think that this would keep the car from cranking.
The clutch circuit is the one I think is to blame for the starting issues. I first wired it in like it was in the 95, but looking at the starting circuit on the 04 diagram, I realized that while the 95 grounds the circuit with the clutch start/cancel switch, the 04 does not, so I rewired the circuit, with no difference in the result. The first circuit also includes the reverse lights spliced in, and I ran power from the battery through a 10a fuze rather than from the ignition switch, but I realize now that may have been a mistake. The second take on the wiring is based on the diagram for the 04 Tacoma, and has a wire running from the starter relay, to both the clutch start and start cancel switches, through a 7.5a fuse and to the ST2 position on the ignition switch.
FIRST CIRCUIT
20210324-151955 — ImgBB
SECOND CIRCUIT
https://ibb.co/YcKGdRZ
02 4RUNNER
https://ibb.co/X2bxQb4
https://ibb.co/ThRVhRj
04 TACOMA
https://ibb.co/bQfXkP9
https://ibb.co/qyJrMwM
95 TACOMA
https://ibb.co/L5D7kYL
https://ibb.co/1K80Mfm
Things I’ve tried
1. Tried to bypass the starter relay, not sure if I did it correctly though.
2. Redid the clutch start wiring to the second version
3. I thought the ECU might not start the car with the interior taken apart because of the odometer disconnect and the airbags, so I put them back on
4. I swapped the old 2002 ECU back, thinking it might change the dash issues but still not start
Possible issues
1. The clutch start switch in the 95 is wired differently than the one in the 04 diagram. I replaced it with a simple rocker switch that should just complete the circuit, as far as I can tell this should be ok and the extra wires on the other clutch switches is for the LED indicator.
2. The 04 wiring diagram shows the wire running from the 7.5a fuse to the ST1 position on the ignition switch. The 2002 4Runner has no ST1 position, so I spliced the wire to ST2 instead.
3. The Tacoma ECU I bought has had the label worn off, so it’s possible that its not the correct one. However, the scrapyard I bought it from confirmed the parts number I was looking for, and when I plugged my old ECU from the 2002 4Runner back in, the same issue persisted. I would expect it to still not start, but the odometer and dashboard problems did not change.
4. Maybe since the 4wd circuit is different, having the 4wd Pin in the ECU is causing problems?
5. The issues with the dashboard make me wonder if there is a blown fuse or bad connection somewhere
6. There is an autostart wired in the ignition that I didn’t know was there until I took the dash apart, but it never affected starting before
7. The wiring diagram for the starter relay and the actual wiring are different. The 02 diagram shows ground on position 2 and the wire to the ignition switch and ECU on position 1, the wire colors for those are swapped on the actual relay. I don’t think this would make a difference, and I assumed that the white with black stripe was the ground as it always is, even though it was on position 1 instead of 2.
I’ve honestly got no clue left what’s gone wrong. As far as I can read the diagrams, things should be working, but this is my first time doing serious automotive wiring. I know a couple people on here have done this swap before, and if anyone has an idea for me I’d love to hear it. Thanks.
EDIT - None of my photos seem to be working, trying to fix it now