trouble with making the tach dimmable

[nebrfestiva]

Man I just was reading it a couple of hours ago and now I can't remember what I used in the search to find it.
I am putting in a Summit tach and used the red/white wire like I thought I was suppose to, but the tach goes bright when the dash lights go dark.
Is it something simple that I need to do?
I hate when the brain doesn't want to engage. Lol

[FestYboy]

you're on the wrong side of the load (dimmer). you need to be on the other wire of the dimmer to make it work right.