Upgrades 11. Dash Dial Dimmer

OK so my first drive at night consisted of about a 40mile round trip. I really should have taken the car out for a test first as there were a few issues! The first was that my headlights were way too high, so they needed adjusted once I got back (I think every driver coming the other way pretty much flashed me and my main beam lights were useless as they were pointing too high!) See the Headlight Adjustment post on how I did that.

The second was that the entire dash was so bright it was impossible to really concentrate and see what I was doing, especially as they reflected off the doors as well. Enter the dashboard dimming upgrades.

Part 1 - Dial Dim Control

This relates to the ability to dim the dials only on the dash, the result is that you can fully control the brightness from their default brightness all the way to them being fully off. It can be fully controlled from the drivers seat.

So I searched the forums and found just one post where someone (wiltsathome on the CLSC forum) had installed a dimmer to their lights with quite good results. I decided I'd do this as well as it is a relatively cheap mod to carry out yourself. The dimmer I chose to purchase is this stack dimmer from Demon Tweeks.

For my 420R (2024), in theory you can install this dimmer on the main wire that feeds the dash lighting. This wire actually passed through fuse 6 and is red and white coloured, however this also controls the exterior sidelights, so you would have to find the point where the wire splices off to the dashboard part only and install it there. The loom is very neatly bundled up and doesn't have much slack, so the only was to do this would be to remove the scuttle and go from there. I decided that this was a bit overkill for what I wanted so I decided to simply install it between the dials that I want to dim (so the 5 gauges I have). The other lights will stay bright but I have another little mod for those too on the 620R dash that I have.

So the general idea is that for each dial, you need to replace the red and white wire that feeds it, with one that passes through the new dimmer. This red and white wire comes into the dial at the bottom right of the instrument block (as you look at the instrument face). I decided to use Wago 221 connectors for all this as they are pretty solid and I've never had any problem with them in the past.

• For the first test, I'm removed the speedo dial which makes access to the wires super easy, I cut the red and white wire into two, with enough slack on both sides to work with, and tested the dimmer in situ.
• The dimmer is connected as follows (my dimmer had a violet, white and black wire):
• violet wire attached to the loom side of the red and white cut wire
• white wire attached to the dial side of the red and white cut wire
• black wire attaches to an earth point, I extended the wire using some wire I had around and joined it at the earth where the fuse box cigarette lighter was (for easy access).

Once the initial test was in place, I turned on the ignition and the dimmer just worked out of the box :)

I then chose where I wanted to mount the dimmer and mounted it before wiring it up properly, I chose to mount it on top of the drivers knee panel so I could alter it when driving, a 7mm drill bit did the job and then some 3m double sided tape (Also make sure that where you put the hole allows for the dimmer to sit flush on the top!)

With it all working on one dial, I decided to wire it as follows, excuse the poor diagram. Basically the white wire from the dimmer has to replace the red/white wire on the input of each dial, For ease I chose to take a single wire from the dimmer to the side of the 3 smaller dials, and then split that again, I also took the earth that way too. It was very easy to secure all the wires to the existing loom with ties to keep them up and out of the way, especially with the dials take out and a light shining up under the dash. I also chose to take 2 feeds from the loom (rpm and speedo) into the dimmer positive 12V wire (just to double it up!!)

Each Wago was also given a wrap of insulation tape just to be sure, and then also zip tied to existing loom points. It's worth nothing that the above doesn't have all the Wagos I used, I also used a few "2" blocks to extend wires to make it easier.

And the result: