About the only way to prevent this from happening, is to get some relays and put them in series of the headlight's power wire. That way, your switch only has to supply enough current to power the relays, and not your headlights. You can pick up a relay for a couple bucks, wire for a buck or two, female connectors for a buck, and all you should need are some simple tools. Cost to do both your headlights would be about $10.
Using a 30 amp SPDT relay, connect terminal #87 to constant 12 volts positive with a fuse rated to the sum of the additional accessories you've added and the components you need to turn on. (If you have two fans rated at 5 amps each and a neon light rated at 10 amps, you would use a 20 amp fuse plus 200 ma for each amplifier and processor.) Connect terminal #85 to ground, terminal #86 to the remote turn on wire from the head unit, and terminal #30 to each accessory with an appropriate fuse. A fuse (not shown) could also be used between the output of the relay (#30) and the remote turn on wire of the amplifiers and/or processors for extra precaution.
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Using a 30 amp SPDT relay, connect terminal #87 to constant 12 volts positive with a fuse rated to the sum of the additional accessories you've added and the components you need to turn on. (If you have two fans rated at 5 amps each and a neon light rated at 10 amps, you would use a 20 amp fuse plus 200 ma for each amplifier and processor.) Connect terminal #85 to ground, terminal #86 to the remote turn on wire from the head unit, and terminal #30 to each accessory with an appropriate fuse. A fuse (not shown) could also be used between the output of the relay (#30) and the remote turn on wire of the amplifiers and/or processors for extra precaution.
