I don't know exactly what you are intending to do here but the ignition switch should be fed from a circuit breaker or fuse protected source. The run from the ammeter to the starter, and from the ammeter to the headlight switch is not fused or protected. Mostly everything else except the horn, is then fed through the headlight switch assembly and protected by it's circuit breaker. You don't want to run a feed unprotected to your ignition switch.
These comment are assuming you have an AD truck.
