I've got most of my wires sorted out and began repinning one of the harnesses when I came across a wire that was much thicker on the recipient vehicle than the donor. Is this an indication that I've made a mistake, or is it okay to solder the thin donor wire to the thick recipient wire?

 

What wire?

 

It was the Tacoma ECU E5 pin 7 (green) to the 4Runner IH1 pin 22 which is a slightly thicker wire (black-red).

It's for the clutch start switch.

 

I took a look at the only Taco EWD I have and do not find a green wire that would be something that you would be splicing. Also, there should not be a wire from the Clutch start cancel that goes to the ECM. That essentially is handled inside the trucks wiring upstream of the starter signal wire.

The large B-R wire is IGN2 in the vehicle in the IH1 or IH2 (dont remember which). I cant see how you should be connecting that to anything related to the clutch start. You will use it, and it is OK to splice to a smaller wire, but I think that you may have something going in the wrong direction.

 

You should try to use the same gauge or slightly larger. Smaller is not recommended.
If the wire is for the engine compartment, I'd look at the heat rating. You don't want the engine heat to melt the jacket and cause all kinds of shorts.

 

dnt 'n ant: thanks for posting. I'm out of town and won't be back until next week. I'll follow up then.