Tachometer

I have a 1984 944 and when i got it, the tachometer wasnt working. Im pretty sure its some electrical problem since the mpg meter on it works. Does anyone know where the tach is connected in the engine? Ive been looking for a while and cant find it. Also, I'm pretty sure I'm not the only who suffered from the leaks in the passenger side from the battery compartment. If anyone has sucessfully solved this problem please help me out, i dont know whether to use waterproof paint or weld another plate of metal in the compartment. thnx