Here's how to wire up a "self-latching relay" for your clutch switch. Choose a relay with 2 sets of contacts called a DPDT (double pole double throw) relay. Each set of contacts has a C (common) terminal, an NO (normally open) terminal, and an NC (normally closed) terminal. One set does the self-latching by feeding the coil hot input through the NO and the C terminals. The relay won't operate until those 2 terminals are momentarily jumped by the "kill" enable switch. Then the relay stays on, and only turns off when coil input power is removed. That is the "kill/enable" part of the circuit.
The other set of contacts control whatever you need controlled by this self-latching relay. To be even more effective, use 2 momentary switches near each other (one hand operation) or far apart (two hand operation. Both buttons must be pressed at the same time.
simulate this circuit – Schematic created using CircuitLab
To use this circuit: 1> turn on ignition. 2> press button(s). 3> relay is now latched on. 4> use clutch/starter circuit to start car normally. 5> when IGN is turned OFF, the relay unlatches.