When I say that you should try to wiggle the switches, it wasn`t to check if they was loose or not.
Turn on the ignition and light (you don`t need to start), watch the behaviour of the warning lamps
while gently wiggling the switches.................if isn`t solid on all the time you have possibly found
the source for your problem.
BTW. The pictures is in a international language, not German.
Inge K.