To make a self-resetting interlock for your ignition or fuel pump, you need
a generic automotive relay such as is pictured in the attached link.
The actuator contacts are numbered 1 and 2; the power contacts are numbered
3 and 5. Bosch relay contacts are numbered differently: the actuator
contacts are numbered 85 and 86, and the power contacts are numbered 30 and
87. The polarity of any of these connections is not important.
Using the Omron (Bosch) numbering convention,
- Wire contact number 1 (86) to ground.
- Wire contact number 3 (30) to the ignition 12V (i.e. the place where the
fuel pump or ignition used to connect to).
- Wire contact number 2 (85) and 5 (87) together, and connect to the load.
- Connect a normally-open pushbutton between connection number 3(30) and
Now, turn on the ignition, push the pushbutton, and the relay will engage
and stay engaged until you turn off the ignition.
If this is unclear, let me know and I'll elaborate.