I have 1995 honda civic ex with a swapped turbo b18b1 engine. It was givin a performance tune by a well known shop in my area. I recently tried to wire a 12v tacho, but once everything was wired it would not work. I tested all the wires the internet said would be 12v and they all read 20v. What is going on? What would cause this? Is there any way to still wire my tach? Thanks for your help!

 

You may need to replace the 9 volt battery in your multimeter. Especially on the cheap meters, when the battery runs down it will read wrong (too high).

Test on another car, with the engine off, measure right on the car battery, you should measure about 12.6 volts.