Lights dim and then brighten

Sounds like a ground bus in the dash is not tight.

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

Do you have a dimmer for interior lamps? Like a rheostat, a little wheel that you turn up or down to brighten or dim interior lamps. Usually the instrument cluster lamps brighten and dim the same way.
Can you brighten and dim the other interior lamps?

These lights are actuated only by connection of the ground wire(white) to the body to complete the circuit. The only place these connections are made is at the door buttons and the rheostat on the dash that dims the dash lights also when knob is turned counter clockwise to dim the dash lights and clockwise to brighten them and on past that bright point to turn on the interior lights. One of the door wires may be bared and close to the body and arcing, making the lights come on and when the wire warms it pulls away from the body and lights go out. You need to remove the kick panel to access this wire and see if it's still plugged onto the back of the button connection and check for bare spots on wire.

there is a switch on the drivers side dash left that dims or brightens all your dash lights it also turns on your cab light make sure the switch for your cab light is set to the right setting

not sure about that one but there is a dimmer wheel by the light switch. move it up and down to dim and brighten the dask lights/cluster. wheel may need replacing. also work the lights on and off switch manually to see if there every thing works smooth or hopes from dim to brite.

if you are saying that the dash lights go dim and bright while driving it could be a loose connection of the wiring harness behind the speedo nacal.

there is a regulator for the display brightness, you may have it turn'd down or it has stopped working;. it controls the brightness at which the dash lights are. usually has a speedo sign on it. goes up and down. it works with the main light and is conecter to them on the same lighting board if it has gone then a new light swtch control switch will be needed.

Yes this can be a normal condition caused by load being applied to the headlights and that lowers the voltage, the lites dim, then the load is removed and the lights brighten. Typical loads that cause this are AC climate control related. Have the Alternator load tested to confirm there is no problem in the charging system. Also have the battery tested, a battery that is starting to fail can cause this problem as well, a failing battery takes a huge amount of charging system power to keep it up, so that makes the lighting see higher spikes in voltage

Check your owners manual. There must be a way to dim the dash lights. Should be a dial or a knob somewhere.