relay issue

Would anyone be able to tell me the farthing points for fuse box relays. One of my relays keeps clicking while driving until I put my foot on the brake or I put an indicator on. I'm guessing it's an earth issue or could it just be a faulty relay. Btw it's on a 75 super. Cheers Adam

Here's the wiring diagram for ya. J2 is the relay in question.

75 Superbug wiring diagram

You'll need to chase the brown wire coming from the relay to see where it goes too.

Interesting that the brake light stops it clicking as only thing it has in common is the rear light housing earth point.