You need to see what runs through the ignition switch. High amp equipment really should NOT be run through it and can cause early failure.
The right answer is an ignition solenoid to power most everything with the ignition switch only serving as the "signal" to close the solenoid.
Put an ammeter on the wire coming from the ignition switch and start turning on things that only work with the ignition on-- dash HVAC fan, perhaps headlights, etc. If amp reading stays relatively low, you are fine. If they go up, consider a solenoid/relay to power the heavy draw things.