98 Subaru Legacy GT phase 1 4EAT "power mode" mod. This changes how the transmission shifts, like a more aggressive tune at the flip of a switch. (It also won't let the torque converter lock up, so don't use this mod at hwy speeds for long.) I haven't come across a very good pictorial on this install/mod besides that link. So, here we go!
First, I chopped the 3 TCM plugs out of the junkyard to make for a clean install. This 20 pin connector is where you will add a grounding wire.
The TCM is bolted to the brake pedal mount. Unbolt it to make this easier.
This is the empty slot where the wire goes. (I marked it in white.) It's the only empty one in that row of wires on this 20 pin connector.
I used the smaller connector for my wire. Carefully cut it apart and remove the desired color wire. I used red for this part of the demonstration using the junk plugs but chose the solid black because there isn't a solid black wire in the connector already. Plus it's gonna be a ground wire.
Press in the little tabs on the side to release the little flap. Poke your new wire into the slot in the same orientation as the others until you hear/feel a "click". Close the flap and you are pretty much done.
Here's the TCM pinout. All you have to do to turn on "power mode" is ground that pin 4 on the TCM diagram. So hook it to a simple on/off switch of your choice. One wire from the new pin to the switch and one wire from the switch to a grounding point (bare metal) inside the dash.
Used this simple/small/cheap switch that fits perfectly in the cluster trim and matches the KC light switch on the opposite side. I also have the Euro LHD shifter assembly with the OEM button on the shifter handle but I don't like that bulky shifter, lol.
**Warning: I'm not responsible for you frying your transmission or TCM if you choose to do this mod and mess up or drive dangerously afterwards. Read through the forum link and be safe.**
