560sel rev counter not working

[mutley666]

I am having problems with the instument clocks on my merc,
The rev counter does'nt work neither does the computer thingy in the right hand side of the clocks, Any ideas?
all the other stuff works, oil press,water,fuel gauge so I am baffled!
I have pulled the clocks out but all the plugs seem to be ok!
Any ideas!!!!