Dash lights go dim when lights are turned on

Back lighting or warning lights ? check engine , ABS , air bags , seat belt , oil light etc... ?
Interior Lamps Dimming
The second group includes lamps which may be dimmed. This group may use a combination of vacuum fluorescent (VF) illumination and incandescent lamps.
• Power window switches
• HVAC control head assembly
• Radio
• The instrument panel cluster (IPC)
When the ignition switch is turned to the ON position, the vacuum fluorescent (VF) display (radio) turns on at maximum brightness. When the park lamps are ON all incandescent back lighting turn ON at the dimming level indicated by the IP dimmer switch. At the same time all vacuum fluorescent (VF) displays dim to match the indicated dimming level. When the headlamp switch is placed in the PARK position, the park lamp supply voltage circuit provides an input to the body control module (BCM). The BCM then supplies voltage to the instrument panel dimmer switch through the instrument panel dimming lamps control circuit. The setting of the instrument panel dimmer switch determines the amount of voltage that the instrument panel dimmer switch supplies to the BCM through the instrument panel dimming lamps low reference circuit. The BCM then sends a pulse width modulated (PWM) voltage to all the interior lamps. All the vacuum florescent (VF) and incandescent back lighting lamps are provided a specific voltage and are then grounded. When the headlight switch is turned to the PARK or HEADLAMP position, all incandescent back lighting turn on at the dimming level indicated by the IP dimmer switch. When the IP dimmer switch is moved from MIN to MAX, all vacuum fluorescent (VF) displays, as well as all incandescent back lighting respond from Minimum intensity to maximum brightness in response to the IP dimmer switch.

I would have it checked for DTC'S - diagnostic trouble codes stored in the BCM !
DTC B2624 Display Dimming Input Range/Performance
The body control module (BCM) supplies voltage to the instrument panel dimmer switch through the instrument panel dimmer switch signal circuit. The dimmer switch varies the voltage and returns the new voltage to the BCM through the dimmer switch signal return circuit. The BCM uses this voltage to determine the illumination level of the instrument panel lamps.

DTC B2625 Display Dimming Pulse Width Modulation (PWM) Output Circuit Range/Performance
The body control module (BCM) receives a variable voltage from the instrument panel (I/P) lamp dimmer switch. The BCM uses this signal in order to vary the illumination level of the I/P lamps. The I/P dimming lamps output from the BCM is a pulse width modulated voltage supply used to light the I/P lamps. If a malfunction occurs in the I/P dimming lamps output circuit, this DTC is set.

DTC B2662 Park Lamp Switch Circuit Malfunction
The park lamps are controlled by the turn/headlamp switch. Positive battery voltage is supplied to the switch through the EXT LP fuse. When the turn/headlamp switch is placed in the park or head position, battery voltage is supplied to the park lamps. The body control module (BCM) is also connected to the park lamp circuit to sense whether or not the park lamps turn ON when the low beam or high beam headlamps are turned ON. The BCM also uses the parklamp battery positive voltage to power the instrument panel (I/P) dimmer output circuit. If the BCM senses that the low beam or high beam headlamps are ON and the park lamp input is not active, DTC B2662 sets.
Do the park lamps work ?

is it adjusted by the light switch left on bright right dim all when lights are on all dash lights will dim thats normal

The sensor is usually located on the top of your dashboard. You might see it if you look into your vehicle through your windshield at your dash.
I have seen( one time ) that a gps was bright enough that it caused the dash lights not to come on because the sensor thought it was light outside.
Or you could have gotten a bad sensor.

a little complicated but here's the deal. most dash light dimmers are really a rheostat and by what you are describing, the coil portion of the rheostat is 'fried' but this will still allow the non-dimming portion of the coil to operate non-dimmed. the dome light part of this is actually another separate switch that is engaged once the max dash light adjustment is reached, it has little to do with the dimmer what-so-ever. This is at least a $200 (or more) repair from a good shop, could be even pricier at a dealership, not counting the dimmer itself.

YOUR DIMMER SWITCH HAS SHORTED OUT CAUSING IT TO STAY IN THE CLOSED POSITION THE DIMMER SWITCH OR ACTUTATOR IS LOCATED UNDER THE STEERING WHEEL PANEL JUST ABOVE THE BRAKE PEDAL ON THE COLUME CALL OR GET ON LINE TO AUTO ZONE AND LOG ON AND YOU CAN GET A PRICE CHECK FOR A DIMMER SWITCH ACTUATOR LISTED UNDER PARTS REPLACEMENT IN THE ELECTRICAL SECTION

Dash lights have much to do with the outside lights. There is factory built in system with the dash lights. When the car is driven during night time the dash lights automatically become dim to eliminate the eye irritation to the driver.
If it is equipped with dimmer switch the variable resistance or its electronic circuit may be defective and be replaced.

Do you have the dash light dimmer control turned dwon to dim?

i don't have a real good answer, soooo just remove the dome light bulb so you can drive it

I know this sounds trivial, but make sure you or someone didn't inadvertently bump the dimmer switch. If you slide the dimmer all the way up and even past the slight little catch so that they are continously on high and still seem dim, there could possibly be an issue with the dimmer switch itself.

To dim your head light, pull your turn signal switch. To dim your dash lights, rotate the switch by your head light switch