I have often run a wire around a broken trace on a circuit board. This will require thinking outside the box. Here are some tips. If you solder to a trace remove the coating from the trace. Tin the trace by heating it with the soldering iron and using a small knife scrape the coating off. Tin the trace while the knife is exposing the metal. Be careful to not get the trace too hot some traces lift off very easily. If the gap is real short then leave a long pig tail on the jumper wire and cut it off after it is solid. You may be able to get your jumper wire from one strand of stranded wire. You may be able to exposed solder on the pcb with the aid of an ohm meter. Glue the jumper to the pcb with some dabs of glue. -denis

The method that I like is to turn on the dome light of the source vehicle and rev the engine just enough to keep the light from dimming. Also if you let the primary vehicle charge the secondary vehicle battery then there will be more current available for starting. Denis