the left one. before i did a retro i had the same problem with the hi/lo 9004 hid kit in that light.
the issue - when the hood is latched or i slam it down it presses the L headlight down a bit (talking about a few milimeters only) - 97/9 depo hedlights so not a perfect fit but close - the hi beam sometimes/often doesn't come on.
when i flip the brights on and release the hood latch OR bump the headlight housing OR go over a bump the solenoid (e46 now and moving bulb before) catches and the hi beam comes on.
any ideas why and why left only

 

Sounds like something to do with the harness. Have you checked it really well to see if theres a break some where?

 

thought about that but the problem only occurs when the hood is closed. no wires are pinched and there's current going through the hi beam wiring when i flip the switch "on".
i've tested the wiring with the hood open though, hopefuly tomorrow i'll have some time to pull the wire outside and test with the hood closed. hoping that something's just loose and not my solenoid starting to go...