Weird flash problem - can anyone help?

[SG1]

I have an annoying problem with my car, when driving during the day and my lights are off my flash doesn't work at all. At night however when I have my lights on it works as normal!?

Anyone have an idea as what this could be as it's quite annoying!

The car is a 1997 R129 SL320.

Thanks for any help in advance!