I did something like the above using the exsiting wiring to 12v system but ended up with voltage drop to about 10v thought the wire system whilst the motor was turning over and van was hard to start and would fire when I let the key off.I ended up putting a relay on 9v wire and run a supply 12v wire direct from the battery. startes alot better,but if bridging the wires work that would be realy easy. RB