I'm not sure if you've seen this thread, but I do believe it is the best way to do it..
This is how I have two sets of lights wired up.
viewtopic.php?p=478384#p478384
You don't need a voltage meter, I would go to Autozone, or a similar place and buy a test light for about 8$. (http://www.amazon.com/Michigan-Industri ... B000NPT6FM) All you have to do is put the clip to a ground, and put the point to the wire you want to test. The easiest way is to take out the tail light housing, unplug the connector and test away. Have someone in the driver seat, with the key in the run position, (you don't have to have the engine running for the reverse lights to come on) Have them put the car in reverse, have the E-Brake on and don't let them take their foot off of the brake pedal. When the test light comes on, that is your reverse trigger wire. Make sure it is not the brake light wire, by putting the truck into neutral then reverse.
I'm not on the computer that I have my Service Manual on, So the above method is the best way. When I get back to the states and you still haven't figured it out, I will post it up.
The WhiteNight option is a good route as well, But you need to have a trailer harness for it to work properly, unless you do the above method, but it doesn't make any sense to spend more money to accomplish something you can already do.
(If you do have a trailer harness you can atatch the trigger wire to that, and bypass the tail light option).
Good Luck!
