My 1996 C class Mercedes has a number of unusual random problems and my mechanic has never seen it before.

Basically on purely randon occassions the heating will come on full and cannot be turned off (ie if turn on aircond and/or turn off the fan the heating and fan still continues flat out)

The other random problem is the speedo stops and the 3 brake warning lights come on all at once (despite no known mechanical issues and the brakes are fine)

Both these problems occur purely randomly and of course did not occur in front of the mechanic. My mechanic could not find any problems.

Can anyone help point me in the right direction?
Does anyone have any ideas what the problem could be?
Help please.