Tach acting strange

[alexwolf1216]

My tach is acting up. It only moves when the transmission shifts. For example, it starts out bouncing around the 6000-7000 mark in 1st, then when it shifts to 2nd it stablizes at 6500. Finally, when it goes into third, it moves to 6000 and holds firm. I am about to pull the binnacle to replace some blown bulbs, but I dont have a clue where to start. Im guessing its something electrical but how would it get tied into the auto transmission?

[Delorean Industries]

My tach is acting up. It only moves when the transmission shifts. For example, it starts out bouncing around the 6000-7000 mark in 1st, then when it shifts to 2nd it stablizes at 6500. Finally, when it goes into third, it moves to 6000 and holds firm. I am about to pull the binnacle to replace some blown bulbs, but I dont have a clue where to start. Im guessing its something electrical but how would it get tied into the auto transmission?

tach is starting to fail. Replacement is required.