Long story short: I have 4 DEFI gauges that are no longer illuminating properly. When I put the key to the ON position, they are nice and bright, but as soon as I turn the ignition on, they change from bright to dim.
This is an issue during the daytime when they should be bright, they are now very hard to see. At night it doesn't matter because they are supposed to be dim with the headlights on. I would only expect them to dim when the headlights are on, but nothing happens when I turn the headlights on/off. They USED to illuminate in the day and dim at night, but something has changed and I cannot put my finger on it.

I pulled apart my dash trying to figure out what might cause that behavior. I can see that each of the 4 gauges have Red and orange going to power (actually connected to little white fuse boxes) and then the lines are connected or tapped into the radio harness, as well as the white wire (which I believe should be used for the feature I am looking for).

I opted to use an "add a fuse" to replace the power wire (which had been tied into a green wire underneath the driver side wheel well) and switched it to use a 10A fuse in the radio position of the fuse box under the wheel.

As far as things that have changed since they did work: Nothing. The only real thing I did was replace my taillight bulbs with LED's, but I can't see what that would have to do with anything (and I also can't recall if the gauges were working how I wanted them to prior to this).
I have a brand new Redtop battery that I just installed as well, so I know that is good.

Thanks for any help.

Below is a link to a video I made showing the behavior, in case it helps:

 

Really dumb question that I'm sure you've tried: have you tried turning up the brightness on the control unit? I know it sounds stupidly simple but it's worth an ask. I have to whenever I unplug my battery.

 

Not a dumb question. So....I actually don’t use a control unit! The car didn’t come with one, and they have seemed to work fine without them. I’m sure getting one would resolve the issue but they seem to be hard to find.

 

So as an update: I went ahead and snipped off one of the white wires coming out of the one of the DEFI gauge pods. This was connected to a wire that was then seemingly spliced into the stereo harness. The test worked: Obviously doing this, the gauge is now illuminated permanently. So I may just leave them like this. I’d still like to know why they are no longer dimming....