I found the Roush boost gauge really annoying at night, way too bright. According to Roush there are only white or blue backlight light options and they can't be dimmed but I decided to dive in and see if I could somehow make it less annoying. My goal was to make it dim with the dash lights and dimmer switch. Ultimately I couldn't get that to work very well but I WAS able to make it 100% more livable at night without resorting to tint film or a hokey dimmer knob stuck somewhere that required constant fiddling. Now, the gauge lights up its normal super bright white during the day and switches to a much dimmer red when the dash lights come on.
I did try two different styles of aftermarket LED dimmers. If you tie the red and white gauge wires together and then to the Autometer dimmer it does work, sort of. If you leave it dimmed the gauge wont turn on. Every time you get in the truck you have to turn the dimmer all the way up to turn the gauge on and then dim it back down. There's also no way to have it full bright during the day and then dim with the dash lights, you’d have to manually adjust it each time. Apart from those issues the gauge doesn't dim very evenly and the needle gets twice as dim as the background. Could work but I wanted something more factory-like.
What I did was build a small relay harness. There may be different ways to do this but I used what I already had on had and accomplished my goal. There is one caveat and that is if you dim the dash lights way down it will buzz the relay, its not an issue for me because I never turn them that low. I may brainstorm a solution for that to make it more foolproof. The attached pictures show the wiring diagram and how I physically laid everything out. Most of the connections to make are jumpers between the two relays. It can be mostly built on the bench. I used Deutsch connectors to the gauge and to the truck but you don't have to. Basically just need 2 SPDT relays with matching terminals, some wire, some heat shrink, basic wiring tools. The diagram shows all the connections to make.
I did try two different styles of aftermarket LED dimmers. If you tie the red and white gauge wires together and then to the Autometer dimmer it does work, sort of. If you leave it dimmed the gauge wont turn on. Every time you get in the truck you have to turn the dimmer all the way up to turn the gauge on and then dim it back down. There's also no way to have it full bright during the day and then dim with the dash lights, you’d have to manually adjust it each time. Apart from those issues the gauge doesn't dim very evenly and the needle gets twice as dim as the background. Could work but I wanted something more factory-like.
What I did was build a small relay harness. There may be different ways to do this but I used what I already had on had and accomplished my goal. There is one caveat and that is if you dim the dash lights way down it will buzz the relay, its not an issue for me because I never turn them that low. I may brainstorm a solution for that to make it more foolproof. The attached pictures show the wiring diagram and how I physically laid everything out. Most of the connections to make are jumpers between the two relays. It can be mostly built on the bench. I used Deutsch connectors to the gauge and to the truck but you don't have to. Basically just need 2 SPDT relays with matching terminals, some wire, some heat shrink, basic wiring tools. The diagram shows all the connections to make.
