Relays, great things...
You could use one (if the amperage rating is high enough) for the amp, controlling the power to it.
I used two relays to control the power going to the headlights, one in line with the high and one on the low beam wires coming from the high/low switch to the head lights. Use the stock wires to control the relays and run new wires from the battery (fused) to the relays then to the headlights; you will notice an increase in the light output.
Back up lights should have a relay too controlled from the shifter switch, run a new larger gauge wire from the battery (fused again) to the relay then to the lights in the rear.
If you don't already have a relay on the horn (should be) then the same idea applies to the horn as the headlights, more juice more noise.
If you have additional communication radios, I have one that requires 25 amps and another needs 15 amps so I use relays on them.
I am not sure what year your vehicle is, mine is an '82, but here is one. Add a relay that allows you to flash your head lights if you are passing a vehicle or if someone passes you, you can indicate to them that they are past you and it is OK to cut in. Use two relays one on the high and one on the low beam wires activate both relays at the same time with a Push Button Switch on the dash. (If you do the above headlight relay mod to brighten your headlights, put these relay between the switch and the brightening relays). Wire up the relay for normally closed so everything will work as if there are no relay until you press the button then headlights will go off for as long as the button is pushed. Wiring both relay to activate together breaking the juice flow no matter which wire has power and will allow you to flash the lights no matter which beam is on, if low beams are on then there will be no power in the high-beam relay and vice versa.
Any question, feel free to ask, sorry if you are confused with my writing, not my best thing to do.
Later, Little long but hope it works.
Do it right the first time !