Odd tachometer problem when warm

[rneedham1979]

My tachometer has been functioning intermittently. When the temps are 85* or cooler the tach works just fine, when the temps start to elevate or if the car is parked for an extended period in which the interior temp elevates the tachometer will stop functioning. As soon as it cools off it works fine. Has anyone had or heard of this before, or do any of you know the possible fix. Everything else works BTW.

Thanks!