Tach install: power source?

[shotty]

Installing a 4k RPM C60 tach, and according to https://www.steelsoldiers.com/threads/factory-tach-install-will-it-work.100057/post-2179753 " When you wire in the tach, do not tap into the ignition 12+ wire in dash wiring harness, when the glow plugs cycle, it kills power to the dash, so the tach will read zero when the glow plugs are lit or cycling. "

That... doesn't sound right me. Of course my truck is in pieces right now so I cant verify. I would love to use the ignition power going to the dash already as that makes sense. Any ideas?

 

[chevymike]

That doesn't sound right. Sure when the glow plugs cycle, the voltage drops but it doesn't turn off.

 

[shotty]

That doesn't sound right. Sure when the glow plugs cycle, the voltage drops but it doesn't turn off.

Yup that's what I was tracking. It's not like all the dash lights and stuff go out when the glowplugs cycle.. I'm going to tap into the brown wire at the cluster, which is the ignition switched 12v source. Hopefully it works out