Trying to fit some spots to the SJ, but WTF?

[SB118]

I've got a handful of lights to hang off the front of the SJ, but i'm hoping to wire them with the relay activating from the mainbeam circuit to be sure i don't go blinding anybody.

Now the tricky bit. I've pulled the 3 pin plug off the back of the headlight bulb and put the tester in to find out which one i need to splice into.

And they're live. All of them. Main, dip & return. The tester (connected to the chassis) lights up on all of them. WTF is going on?

Any ideas?

 

[SB118]

Right, been out doing some more testing...

Viewed from the back of the bulb

  2      _
1   3   | |

     OFF    DIP   FLASH    MAIN
1    live  live  live     live
2    live  off   off      live
3    live  live  off      off

So the mainbeam circuit is obviously switching fine, but it's switching to a neutral. How the hell do i trigger a relay from a neutral?