Tach trouble

I just got this boat ($200) and am going thru everything, motor ,outdrive,electrical,ect. The electrical is really giving pain. The problem I would like to resolve today is my Tach. Its a stock 1977 indash original tach. It looks cool so I would like to keep it, if possible. The problem is when I turn the key on , the tach pegs itself at 6000 rpms and sticks there till I turn the key off. I did buy a manual and all the wires look like they are routed correctly. The double gray or brown (cant exactly tell ) was disconected from the neg side of coil. I reconnected it per the manual and the tach still pegs itself with ignition on. Is this tach toast?<br /><br />Thanks in advance. There is a great wealth of knowledge an I appreciate it tremendously