all on switch for multiple led groups

Hi, I'm new here, so forgive me if this is redundant, which I'm sure it is. I tried using the search feature, but turned up nothing after several attempts.

Here's the low down. I have three sets of lights all hooked up to individual [three] switches. I'd like there to be an "all on" switch. I am far and beyond the biggest fool when it comes to relays. I don't know why but my brain turns to poo-poo when it comes to them. Can anyone give me a run-down 'for dummies' on how I would go about doing this?

All help is more than appreciated!

You do not need to use a relay to pull this off.  You can use 3 diodes that are available at RadioShack.  I need to know how you have the LEDs wired up to the switches.  Is the switch supplying the LEDs with positive voltage, or are they switching ground to the LEDs?

How many LEDs are in each group?

I am assuming that you have the switch switching positive voltage to the LEDs.  I am also assuming that you do not have more than 40 LEDs in each group.  If either of these assumptions are not right, let me know before you attempt this.

The lights are 'lightheads'. Each lightead has 6 high power LEDs in it behind a wide-optic lens. Each one is attatched to a +12V switch. I want to have individual control of each group of lightheads, and also be able to switch them all on if desired. Sorry, I should have been more clear before. The switches are set up in a switch box of 4 switches, so I have one position left that I can use and an all-on switch. Since it is a switch box, there is a main 8 gauge +12V wire, each switch is fusable. I hope that clearifies a little bit!