The LED Dash Control Center on my 2005 Mercury Monterey will go from being bright and readable to dim and recently completely off. It is not affected by the dash light dimmer control switch, but does changed it's luminance when the headlights or parking lights are turned on of off. At first I thought it was a heat/cold problem but now it is more random, with it being dim and now off most of the time. Any suggestions on how to make it stay bright and readable?

The problem is very likely the surface mount resistors on the instrument cluster circuit board. If you are handy with a soldering iron, it takes about 1 hour to fix counting taking the instrument cluster out, testing it, and putting it back in. The official removal instructions are at

http://ww2.justanswer.com/uploads/sdcrowder/2010-09-08_003910_instrument_cluster.pdf

And a video showing the resistors is at

https://www.youtube.com/watch?v=s1_FVOVj2ms

As for the official removal instructions, I would modify/add to them as (note: I have a 2004 Mercury Monterey):

1. Tilt steering column to the lowest position
2. Remove steering column cover by pulling up and towards you
3. Open plastic panel under the steering column by pulling on the finger hold just under the steering column.
4. Remove the 5 screws behind this panel holding the cover/panel on and remove.
5. Put on the emergency brake.
5. Turn the key to the on position and move the shift lever as far to the right as it will go.
6. Use a flashlight to find the tiny transmission range indicator cable down the right side of the steering column.
7. Remove the cable from the knob connecting it to the gear shift.
8. Shift back into park and remove key.
9. Remove bolt holding gear shift cable on to steering column
10. Remove the 2 instrument cluster screws.
11. Use a small thin pry bar at the top of the instrument cluster to pull it out. It is just a tight fit.
12. Remove the instrument cluster electrical connector - it has a small clip you have to depress to pull it out.
13. Guide the instrument cluster out from behind the steering wheel (may have to tilt the steering wheel even more to squeeze it out.

Now, to fix the cluster.

1. Gently unclip the five snap clips holding the front plastic case onto the circuit board and remove.
2. Remove the gauge needles by gently but firmly pulling then straight out.
3. Remove all the screws from the back and remove front assembly from circuit board.
4. You will now see the four resistors shown in the youtube video above.
5. Be careful about soldering them because when you heat one side, the resistor might just pop off and then you have to go looking for it. I found it useful to use long tweezers to hold the resistor while soldering and also to use some "no clean" flux with some small diameter solder. Solder both ends of all four resistors and try to do it cleanly so you don't have extra solder floating around.
6. If you want to test this fix, just take the circuit board to the car and plug in the electrical connector (it will make some noise as the gauges try to reset). Turn on the vehicle and see if it lights up.

And as they all say - To install, reverse the removal procedure.

The hardest part is maneuvering the soldering iron to get to all the sides of the resistors.

When the headlights or parking lights are on,the readouts will automatically dim to compensate for night driving. that aside, the dimmer switch is could be bad or the wiring has become loose or disconnected or the connector on the readout is loose or has become disconnected. my odometer was randomly going on and off. and tured out to be a loose connector