This post deals with wiring the reverse lights on an automatic to manual conversion, using existing wiring (mostly).

I performed the following on a 1994 Civic EX S24A automatic transmission conversion to a 2000 S20 manual transmission.

All of the write-ups that I was able to find proposed running two wires from the reverse light switch under the hood (through the firewall) to the automatic shifter electrical connector inside the car (apologies to anyone who wrote such a post - I was not able to find it). The following technique uses the existing lockup solenoid wiring to eliminate the need to pull new wires through the firewall.

NOTE: This does involve cutting two wires from your ECU harness. Proceed at your own risk.

Assumption 1: The automatic transmission that you are replacing had/has lockup solenoids (see image).



Assumption 2: You have cut, or will be cutting, the wires between the automatic shifter lever and the shift lever connector (C409 - I used the following write-up: http://brokenlimits.powweb.com/howto...automanual.htm. Although, unlike the write-up, I wired a relay inline for my clutch pedal disconnect switch. Here's a write-up on adding a relay: https://honda-tech.com/forums/honda-...8557/#34826076).

NOTE: I did install a manual transmission PGM-FI/ECU as part of my conversion. I don’t see any reason why these steps would not work with the original ECU. But, just saying.

Here are the steps.

You will discover after installing the manual transmission, that the lockup solenoid connector plugs perfectly into the connector for the backup light switch (see image).

• Remove the passenger side kick panel and unbolt the ECU/PGM-FI mounting hardware.
• Locate the C404 connector on the ECU (see image).

• On the C404 connector, locate the yellow wire going to pin 10 and the green wire going to pin 9 (see image - I’ve reversed the diagram, as this is the orientation of the pins when you’re looking at the female side of the connector, with the wires going away).

• Depin or cut the yellow and green wires (I cut the wires. I failed using a couple of different depinning techniques).
• Run two wires from the shift console connector (C409) to the ECU connector (C404 - I ran yellow and green wires as the wire colors match on both sides). Tip - Removing the glove box (two phillips screws) made it easy to route the wires.
• Splice the two wires to position 5 (yellow) and 4 (green) on the shifter connector (C409 - yellow and green at the bottom of the following image)
  

• Splice the two new wires to the loose wires that you’d cut from positions 10 (yellow) and 9 (green) on the ECU connector (C404). You should now have yellow to yellow and green to green connections on both sides.

• Connect the lockup solenoid connector under the hood to the backup light switch pigtail on the transmission (it’ll plug right in - :-D).
• Turn on the ignition and put your transmission into reverse. The backup lights should work.

NOTE: Don't forget to plug the connector back into the ECU before you start the car.


Personal (non-technical) experience:

When I was re-attaching the wires under the hood, after the manual transmission install, I discovered the lockup solenoid connector plugged perfectly into the backup light switch pigtail. All of the auto to manual posts that I’d found, dealing with reverse light wiring, suggested running new wires, through the firewall, between the shift connector and the reverse light switch.

I had a hard time accepting this solution, because I was confident that the wires that had been connected to the automatic transmission lockup solenoids were no longer needed to serve that purpose. So, they might be re-used to serve my purpose (wiring for the backup lights). And, save me the effort of running/routing/protecting two new wires across the engine bay and through the firewall. This especially since the connectors were perfectly identical.

I continued my research, but was unable to find any posts/videos, on the auto to manual conversion, that referred to this coincidence (which I found surprising). So, I resorted to the repair manual. There I located the backup light wiring diagram confirming that the connector operated the lockup solenoids on the automatic transmission. And, operated the backup lights on the manual transmission.

From there I located the PGM-FI wiring diagrams covering the lockup solenoids. And, the wiring diagram dealing with the backup light switch.





Which confirmed for me that the C110 connector (with yellow and green/black wires) that powered the lockup solenoids wires was the same connector used for the manual transmission reverse light switch. Which meant that the lock up solenoid wires that lead back to the ECU could in fact be used to power the backup lights.

Apologies for the bold text. I pasted this from my word processor and was unable to disable the bold text. I'm happy to answer any questions as I've become a bit of an expert on this subject specifically. But, I am by no means a auto to manual conversion expert.

 

Not a bad idea to use wires that are already there.

 

Great write-up! I added this to the Stickied FAQ thread.

The engine harness itself for 5th gen civics is actually identical between automatic and manual civics. Honda just did what you did and used the lockup solenoid wiring for the backup lights, wire colors and all are identical. All of the wiring differences are in the under dash harness that runs across the inside of the firewall and out to the passenger's side headlight and horn.

 

Great!! This is akin to what I did for both AT->MT swaps I've done.

BTW, here is a primer on dealing with those pesky ECU pins: Honda CIVIC EG6: OBD1 ECU Plug - Pin Removal