Ok, I've found the trouble : the 12V of rear light must not be connected to the permanent 12V battery but to an accessorie 12V witch send 12V when ignition is on.
To resume : under front cover, you have two set of wires left. One set with 2 purple wires and one set with 3 red/white wires. Connect your rear light like this : the ground light to the set of 2 purple wires and the 12V light to the set of 3 red/white wires.
And then, it works great.

 

I hooked up a reverse light on my 1993 350L last spring and this is how I did it. Sounds like the wiring has not changed all that much since 1993. I traced out the purple wire and found the terminal to which it is connected. This terminal on my model was located under my airbox and right on top of the transmission where the shift linkage attaches to the transmission. I pulled the purple wire loose from the terminal and after examining the terminal I went to a hardware store and found a piggyback connector of the correct type. Make sure you use insulated terminals to avoid a potential short. I think a lot of car stereo places also carry these piggyback connectors. I then inserted one end of the piggyback terminal into the terminal where the purple wire had formerly been. I then plugged the purple wire into one of the piggyback connectors. This left me one more piggyback connector which I hooked another wire to, and ran that to the backup light (+)side. I then ran a ground (-) from a chassis screw to the other wire of the backup light. I have had no problems with it at all since installing this. I realize that I am pulling another 5 amps through the reverse indicator light circuit, but the wire is plenty heavy enough for the added load. I don't know if this circuit is fused or not, but I have had no troubles.
I also wanted to be able to operate the light whenever I wanted, even when not in reverse. So I installed a lighted rocker switch on top of my highbeam headlight pod and ran this hot (+) wire back to the reverse light and spliced it into the hot (+) wire on the light.
I fused this wire before the switch just to be on the safe side.
Now I can turn on the reverse light either by shifting into reverse, or by throwing the lighted rocker switch on.
The only irritating thing about wiring it like this is that when you use the rocker switch to power the light the reverse indicator light comes on. Even when your not in reverse!!
This is because current is backfeeding to the reverse indicator light circuit from where the 2 hot wires are spliced together.
All in all I love this setup because I have light behind me whenever I need it. Whether backing off the trailer in the dark or hooking up my little pull behind ATV trailer I always have light on the subject now!!!
I hope this post helps you guys with the newer machines. It sounds like at least some of the wiring is the same.
I found the purple wire to be a hot wire on mine and not a ground wire!!

Doug

 

Just be carreful if you add a switch like you tell about, on a recent 500 or a 700. Because, the atv will think it is in reverse mode and action the RPM limitor until you depress override button.
To do that on recent model, you need to install a double relay to cut of the first lectric diagram when the second will be on. It's a little hardiest...

 

any of ya'll have pic's of backup lights on your quads? I'm thinking of adding one to my 700. my pic's