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Auto-to-Manual Part 2

Auto-to-manual conversion: the how-to continues.

By Brian Gillespie

Our project car is a 2004 RSX base model and that effects the wiring when going from auto-to-manual. The following modifications work on the 2001 to 2004 models of RSX. If you have an 05 or 06, there will be some differences. I strongly suggest getting a Helm service manual or electrical troubleshooting manual to help with wiring if you have the later model. The manuals are available at helminc.com.


Since this is a base model RSX the K20A3 only makes 160 horsepower so just switching to a manual transmission will get more power to the ground.

To first thing we did to prep for the new transmission was drop the engine and transmission. This isn’t strictly necessary, but it made it easier to remove, modify and reinstall the engine harness, not to mention the new transmission. Once again, I suggest getting an RSX service manual from Helm Inc. to help with the removal of the engine. You can buy the manual on line from helminc.com or if you have a PC with Windows Internet Explorer, you can access the information in PDF format online from Honda at Service Express for a small fee. You’ll only get one day of access for your $10 or $20 payment, but you can print the PDFs if you’re a slow worker.

Next up was the shift mechanism. The stock automatic shifter is a huge heavy thing and has some electrical connections for the AT Interlock System. That keeps you from removing the key if the car isn’t in park. These don’t really pose a big problem. Once the shifter is unplugged and removed removed the interlock stops working. Problem solved.


Here is the automatic shifter with the console removed. The shift cable, four bolts and some plugs hold it in place.


Here are the connectors for the interlock and starter cut. Just unplug them.

Installing the new shifter is as simple as bolting it in using slightly longer bolts and the same mount holes as the A/T shifter. The shifter can come from a 5-speed or 6-speed RSX. Mine actually came from a 2001 Civic DX, it’s very similar and about $40 cheaper. The shift cables though have to be for a 5- or 6-speed RSX. Conveniently, the shift cables and grommet seals fit through the same opening as the A/T shift cable.


The shifter and cables for our swap. In my case, I bought the shifter from a manual 01 Civic for $25 and the cables from a base RSX for $50. New the RSX Type S stuff cost over $350.


The manual shifter bolts in using the same holes in the chassis but you'll want longer bolts.

We’ll need a new brake and clutch pedal for our car. You can source them from an RSX or from the 02-05 Civic Si. RC at RC’s Garage happened to be doing a RHD drive conversion in an EP3 and had an extra set of pedals from the JDM Type R. I was able to score the pedals and the clutch master cylinder. The lines for left-hand drive are different so I bought those new. If not for the car at RC’s I would have found an RSX donor car. If you do, I suggest getting both pedals, the clutch master cylinder and any and all clutch lines and brackets.


The pedals can come from several models including EP3 Civic Si, base model RSX and 01-05 Civic. Mine came from a 2003 JDM Civic Type R. Racey!

Unlike Civics and Integras from earlier models there are no holes in the firewall for mounting the clutch pedal. Upon inspection of the firewall you can see where the pedals would mount though. This may not be so hard after all.


On the firewall under the dash, you can see how the insulation is precut for the pedal to mount.


Once I pulled the precut plug out it was easy to see where I needed to make holes. We need to drill these out.

I got all anal and made some paper patterns of the holes so I could make sure I marked the center point and drilled accurately.


I made up a quick drawing to help me determine the center of each hole. I could have just eyeballed it, but then I may have wound up using a rat tail file to move the holes around for a better fit.


I cut the hole drawings our and taped them place. Each one had the center marked which made it easy to drill the holes correctly the first time.

Once the holes center were determined I used a 7/16″ drill bit and 1 1/2″ hole saw to make the holes.


Hole saws don't always like sheet metal. try to keep the saw perpendicular to the piece you're cutting and hold the drill tightly. It will probably try to grab at some point and slam your hand into a sharp piece of metal under the dash.


With the holes drilled, mount the new bake pedal where the old one was and the clutch pedal in the fresh cut holes. The clutch master cylinder mounts on the opposite side of firewall through the new holes. The pedal bolts to the master cylinder.

With the clutch and brake pedals installed there were some new electrical connectors to hook up. The new brake pedal’s switch was the same as the old one, but now there were two new connections for the clutch pedal. The top switch is for the starter interlock so you can’t start the car while it’s in gear unless the clutch is depressed. The one on bottom is for the clutch position. It turns the cruise control off if you hit the clutch. You don’t have to have these switches, but unless you are building a race car, I’d hook them up.

I harvested some connectors for the clutch switches from a salvage yard. You can find them on Accords and Civics that are 5-20 years old.


The connectors a quite common. I found these in a pick it yourself salvage yard from a 95 Honda Accord with manual transmission.

Each of these connectors gets two wires connected to it. One wire from each is going to be a ground, so crimp an 1/4 eyelet on. Once they’re plugged in, find one of the many 6mm bolts or studs under the dash and bolt the eyelet down to ground it. The other wire from each connector will be extended over the passenger side of the car and spliced to wires we will remove from the C101 connector by the ECU.


I added a length of wire to each pin. One black wire each for ground and one one longer wire each to reach over to the area just behind the glovebox.


A 1/4" eyelet gets crimped to each of the black wires. It's a ground so it doesn't have to be an insulated connector.


There are plenty of 6mm bolts and studs under the dash to use as a ground.


The plugs get plugged in and the wires routed to the C101 Plug.

The next mods will be with the C101 connector. Remember it’s the big grey one near the ECU that has 20 openings for pins. We want the car harness side, not the engine harness side.


This is the C101 connector. I have already unlatched the C101 connector's clip that locks the pins in place.

We’re going to make several changes to this connector so you need to know how to take out the individual pins. The connector pins are extracted using techniques explained in this earlier vtec.academy article. Read the part about the OBD1 ECU pins. The OBD1 ECU connectors look a little different, but the procedure is identical. You’ll need a pick tool and a 1mm jeweler’s screwdriver. This is the one I like, it’s made by Wiha and is high quality tool steel. It’s small and durable.


These are indispensable tools for removing pins. If your going to do this on a regular basis, invest in the good stuff. If your going to do it once, invest in the good stuff and then resell it to someone on Facebook or your car club who will need them next.

Remove the light blue wire from pin 6 on C101. Solder it to the wire coming from the clutch position switch. Clip the blue with white stripe wire from pin 3 on C101. Leave at least an inch of wire hanging out of the C101 connector so we can connect to that pin later. Solder the blue/white wire you just cut off to the wire coming from the clutch interlock switch.


These wires came from the auto transmission's range switch on your engine harness and controlled the ignition interlock and cruise control. Now your clutch pedal switches will do those duties.

On 2001-2004 manual transmission cars, the VSS signal for the dash also comes through the C101 plug.  In the automatic cars, and 2005-2006 manual cars, the speed signal comes from the ECU E plug. Since our car is a a 2004 RSX  we need to get the signal to the C101 plug. There is a blue wire with white stripe located in the 25th position of the E plug. Cut that wire and solder it to the short piece of wire you left at C101 pin 3.


This is the wire your old automatic ECU used to talk to the speedometer. You can cut this wire or depin it. The new ECU won't care.

The backup light wiring for the manual transmission also comes through the C101 plug. With the automatic, the transmission range switch grounded a relay to switch on the back-up lights. Now that we have a manual trans, there is no relay, but the reverse switch on the transmission makes the connection to switch on the lights. So we need to remove the relay and move those wires to the C101 plug.

The reverse relay is in this group of relays behind the glove box. The back up light relay has two yellow wires, a green wire and green with a black stripe wire running to it. Clip one of the yellow wires and the green wire from the relay connector.


These are the relays we want to get to. They are mounted to a crossbar that glovebox mount to. Unbolt the cross bar so we can get to the underside of the relays.


These are the two wire we are interested in. Clip them both and peel back the harness so they can be moved over to the C101 harness. There should be enough wire to reach if you peel off the electrical tape.


The green wire is going to go to the number 1 pin and the yellow wire to the number 2 pin. After we plug our manual transmission engine harness into the car the reverse light will work.

The wiring conversion for the chassis is complete. Next up we need to figure out the engine harness and install the new transmission.

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Brian Gillespie
Technical Editor at VTEC Academy
Brian Gillespie fell in love with the Honda brand in 1974 when he owned and raced a CR 125 Honda Elsinore. Many Hondas later he started Hasport Performance with his brother Keith. The last 17 years have been spent developing all sorts of engine mount kits, paving the way for nearly every Honda engine swap that's since taken place.