Best way to shorten or lengthen oem harness

hello , I have a 2010 Camaro ss and I am relocating the abs module and tipm/ fuse box, I need to change the length of some wires to make a harness that is reliable. Anyone that has done this or can give me a few pointers?

G'day Hans.

If you can get new pins for the original connectors, the best way will be to de-pin the original connector, clip off the pins and splice on new lengths of wire. Stagger the spliced in the harness, insulate them with some heatshrink. Then install the new pins on the end of the wires with them being long enough to get where you need to go, repin the them into the original connector body, and you should be good to go.