If you break the neg side and break the fuel pump ground wire at the same time, the car shuts off, fuel flow stops , and the whole wire system has better crash resistance. Smashing the ground wire into bodywork wont start a fire. This also avoids the big hassle of the alt contining to run the car.
The Bosch alt are often self exciting/ firing at around 3200=4000rpm . Check yours. Most will start without a light/exciter wire. For the few that need a light , I use two side marker light sockets and bulbs. The diode is in the alt , glowing the bulbs, key on engine off. When the car/alt fires, the lights go out.
I use this method for the ministock that needs to make a vacuuum rule. I need the alt load to increase the vacuuum so that I can use more cam.
I use two bulbs, because if one burns out the alt will not fire and the car wont make vac, costing me a DQ and money..
FWIW, many race cars have the starter power bypassing the bat break. The break switch does not like the high amps for very long and often results in a no start on the grid with 2 to go.
I dont condone this wiring, but my endurance car has the bat switch that can be bypassed really quickly.
HTH, MM