emergency lights

Hello - long time reader - first time poster....

I am installing an LED lightbar for volunteer firefighter work.  I've installed them in the past where it was switch 1 went to wire 1 and so on.  Here is my question with this bar -The power/switch box I have has a 3-position progressive slide switch and then 5 separate rocker switches.  The slide switch is set up to so position 1 activates the rear of the bar, 2 the rear and sides, and 3 turns on the front as well as rear and sides.  The bar can have individual lights turned on using the rocker switches as well.  If I want to have a rocker switch control the sides and say a front light - how do I tap into the wire that goes to slide switch 3 without also backpowering the other wires (rear and sides)?  I hope this makes sense.  I've considered the use of a diode, but i've never used one and wasn't sure if that is what I would actually need.  Any suggestions would be appreciated.  Thanks in advance. 

This will be a simple procedure using 2 diodes.  If you have an electronic parts retailer near you, purchase 2 NTE 5812s trom them.  Should be about 1.50 each.  Power one leg of the switch, connect the Non-Banded end of both diodes to the other leg of the switch.  Then connect the other leg of the diodes to the lights you want to control.

The above is assuming that the LEDs run on 12 volts.  Also assuming that the slide switch switches positive voltage and not ground.  If these are wrong, let me know so I can adjust the instructions.