Quoted from Lermods:So this is interesting. When I wrote instructions for my camera mod, I wrote them based on connections I made with the game right in front of me. The connections were to the lugs with wires on them and I did not have any lamp issues elsewhere. Now, this was a few years ago and it’s entirely possibke I wrote them incorrectly, but usually my instructions are correct. I don’t have my game anymore so I cannot confirm this, but nobody has come back to me and told me my instructions were wrong. To be safe, I will add a note in my instructions about an alternative connection if an issue arises.
In theory, if you're using a bulb, and not an LED, then adding a bulb from wire-to-wire (and not diode-to-wire), that bulb will bypass the diode, and let current flow to light up other lamps. This would depend on the bulb's resistance, etc as well, affecting the result.
Now, if you have an LED, which is a diode, then if you wire the LED up from wire-to-wire, and the diode's direction matches the same polarity as the diode there on the lamp socket, then.. you'll have no issue. Because the LED is not allowing reverse current, none of the other lamps will light.
So, there are a lot of factors that could cause or prevent other lamps from lighting. (And I haven't even touched on whether the OTHER lamps are LEDs or incandescent, etc..)
Just basing on what @op said in his opening post, I'm taking a guess that the mod has a small bulb in it, and it's bypassing the diod there on the socket.
Of course, I could be completely wrong, too. I often am! Just basing my suggestion on what's been posted so far. I mean, hell, it's possible that his TZ has another socket with a shorted/missing diode, and adding this one just exemplifies the issue.