To attach wires to a firewall or inner fender, I do the following; Usually, wires on the real car are attached with some sort of metal band or plastic clip that is fixed to the firewall. The idea is to try to duplicate this idea.
- Drill a small hole (the smaller, the better) in the fire wall, underneath where the wire will be routed.
- Insert a 1/2" length of very fine black thread (or fine wire, fishing line, etc) into the hole and glue one end to the back side of the fire wall. (I use a .025" -.035" drill bit)
- Pass the free end of the thread back through the hole, leaving a loop.
- Pass the wire or cable through the loop.
- Tug on the free end of the thread, cinching the wire or cable snugly in place on the fire wall.
- Glue the free end of the thread to the back of the fire wall.
I hope this makes sense.
This method provides a neat and authentic appearance, completely free of any visible glue. The wire is held very securely, and by placing the 'clips' in the right places, the wire can be easily routed where ever you want it. It's quick & easy, and almost impossible to screw up. Works well for fuel lines and brake lines on the underside of the chassis, too.