So, the other day I bought a cheapie Equus tach for my '91 Sub. $30, brand new, so I won't complain.

Anyhow, I mounted it, and started to run the wiring. The wiring under the dash is a cluster f**k, so it was definitely trial and error, but I managed to find a hot accessory wire, which one of the previous owners had clipped and taped off. Cool! Makes my life easy...

Got everything hooked up, and had to go to town. So, I'm driving down the road and the tach is going nuts at about 2,500 rpm. Bouncing all over the place. Figured it was the tach wire off the distributor. No biggie...

Then I hit the brakes, and the tach drops to 0. WTF? I let off the brake, and it bounces right back up! Turns out the wire was part of the old trailer brake system. Got it all hooked up right now.

The things that make us feel dumb...