Longtime76

The tach in my 87 944S only works about 5% of the time. Sometime, after a hit a bump, or just randomly it will bounce around some and work for a little while, then when I hit another bump it will stop. I was wondering if anyone knows what the problem is and how to fix it. The car has is going in to get the timing belt tensioned in the next two weeks so I could always have them fix it but they will probably charge me a fortune to do it. Any help would be greatly appreciated.