[TchncnDen]

I used the same Speedway 20 circuit wiring harness with a self modified lsx engine harness so I thought I'd pass along some observations.

I mounted the fuse panel so the letters were right side up. Get over it and mount them upside down so the wiring bundle comes out the top. I'm might flip mine one of these days, but it won't be easy now that it's all wired up.

I think there are six circuits on a plug in pigtail that you probably won't need so don't even worry about them. Remember you'll have extra circuits anyway because things like the fuel pump will be on your standalone harness.

There is no reverse light wire in the Speedway harness. I used the third brake light wire since I don't have a third brake light. I wired the brake lights through the PCM. Wire the relay control with one side to ground and one side to the reverse PCM wire. Wire the third brake light (now reverse) wire to one side of the NO relay contacts and the other side of the NO contact to power.

Wire the neutral safety wire from the PCM to one side of a relay control and the other side of control to ground. Split the purple starter wire on both posts of the relay NO contacts.

If you can figure out where you are going to mount the PCM before you modify the harness, it will be easier to make it look clean that way.

Those are the main things I can think of for now, if you have any questions let me know.