'99 southwind Radio Switch Monoplex

Question is about my (Radio Switch - Monoplex) I have a '99 southwind and the Radio has failure on Left front speaker - intermittently
I found the radio switch but not sure of its function, could this be a problem?

5 terminals - Ing
radio
coach
grn
signal
12v on coach (with key off)
2v on signal
all others 0v

thanks for your help