Could be a cold solder joint or a crack in the foil path within the board.
If you're pressing on those points and the relays come in, then I would suspect the negative common not making good connection somewhere on the board. If you can isolate the point you may be able to solder a small
guage wire across it at the nearest two terminal points. Usually when a relay or starter vibrates like that, it is due to one side or the other not passing enough current to bring it all the way in and hold. |