Just picked up my 05 MCS and during highway driving today the tach completely dropped out for around 5 min then turned back on - and the RPM readout bounced from 3k to 0 like 5-7 times and then stayed steady for the remainder of the trip. Then I just took it out for dinner and thatch again was off (no lights) for the 3 mile trip but worked perfectly fine on the drive back home.

Anyone have an idea of what causes this?

 

Electrical Issues. Good Luck.

 

The tach is probably quitting on you. You should be able to find one on ebay for under $100. Swap is easy. Two screws and a one connector.
Good luck.

 

UPDATE - took it back to dealer of purchase - they found an exposed wire and then replaced the wiring for the tach - all is working well (so far)