Ok...now we are getting somewhere. Since you have 8 wires going in, is it a 8 conductor cable that was used. That would just mean there is an extra unconnected wire....not a big deal.
So we are now back to the single problem of yellow wire connection is bad.
Still the same reason to fix it correctly....so a short does not take out your coach lights.
The best way is a $25 signal wire tracer. Home Depot or Harbor freight.
You clip a signal generator box onto the suspect wire, and you use the handheld detector to trace the wire while it is in the bundle.
So you should be looking for a cut yellow wire, blown fuse, or bad relay.
what kind of chassis?