Head Lights go dim, instrument panel goes dim when I turn on my Headlights

Check where the brightness adjuster is for your instrument panel lighting on your vehicle because there will be one. Sounds from what you have said that this is being moved each time you are turning on and off the headlights because they are totally separate controls.

With out tracing the wiring/voltages its not possible to be sure, but the likely cause is the headlight switch ... assuming you didn't miss any fuses/circuit breakers. Turn signals and brake lights are on an entirely different circuit; so thats not really relevant. The panel, tail, and head lights are all operated thru the same switch (though likely different contacts in that switch), so to be sure you should verify power into the switch vs no power out before replacing it. Hope that helps.

Could be caused by a corroded central grounding point or a blown fuse.

It's normal for the instrument lights (including the overhead panel) to dim when headlights are turned on but this should not affect the dome or courtesy lights.

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Headlight Switch

ABCDEFGHIJKLMNOPQRSTUVWXYZ The headlight switch controls most of the vehicle's lighting systems. Many complaints concerning the lighting systems can be the result of a faulty headlight switch. For example, dim or no instrument panel lights, dim or no headlights, dim or no parking lights, and improperly operating dome lights can all be caused by the headlight switch.
Dash-Mounted Switches
A headlight switch. You'll need to remove the switch to test it. With the switch removed it can be tested for continuity and the connector plug will serve as a test point for the lighting circuits. First test at the connector.
In this procedure the terminals are identified as follows:

• Terminal B = battery
• Terminal A = fuse
• Terminal H = headlights
• Terminal R = rear park and side marker lights
• Terminal I = instrument panel lights
• Terminal D1 = dome feed light
• Terminal D2 = dome light

Consult the service manual for terminal identification for the vehicle you are working on. If this is not listed in a separate chart, you should be able to identify the circuits from the wiring diagram.

• Connect the 12-volt test light across terminal B and ground. The test light should light. If not, there is an open in the circuit back to the battery.

Testing for battery voltage to the connector. Reprinted with permission of Ford Motor Company.

• Connect the test light across terminal A and ground. The test light should come on. If not, repair the circuit back to the fuse panel.
• Connect a jumper wire between terminals B and H. The headlights should come on. If the headlights fail to turn on, trace the H circuit to the headlights. Also check the ground circuit side from the headlights.
• Connect a jumper wire between terminals A and R. The rear lamps should illuminate. If not, trace the circuit to the rear lights. Also check the ground return path.
• Connect a jumper wire between terminals A and I. The instrument panel lights should come on. If not, trace the circuit to the panel lights.

The chart below indicates the test results that should be obtained when testing the headlight switch for continuity. use an ohmmeter or a self-powered test light to test the switch.
Steering Column-Mounted Switches
On some vehicles it is possible to test the steering column-mounted switch without removing it. The test is conducted at the connector at the base of the column. However, on some vehicles it is necessary to remove the column cover and/or steering wheel to gain access.

check your dash light dimmer switch. it is usually by the headlight switch, it might of gotten bumped accidently. if this doesn't fix your issue then i need to know if all dash lights are out or just the ones in the instrument cluster.

You may have loosened a connection when you had the dash apart, but I suspect the headlight switch is faulty.

it sounds like you have a bad connection on the left headlight either the earth or the power wire,check the connector on the headlight bulb plus all the other wiring & connector plugs.....hope this helps.....cheers.

Well...lets start with the obvious. Check fuses and NEVER piggyback any stereo or security stuff into their fuses...you dont want the lights to shut down during a night drive!!
Check under the hood for a relay center...also has some fuses there as well.

The Daytime Running Lamps are a "straight through wiring configuration". Doubt it even goes through a headlight switch at all.
But the regular lights do.
Unless you've worked on the front of the car and forgot to plug the headlights back in, do this...
Turn the light switch on...looking at the instrument cluster , can you make the high-beam-indicator light come on?
As you rotate the headlight switch knob...does the instrument panel lights brighten or dim? You probably have a faulty headlight switch...auto stores have them...they simply plug in.

there could be a shorted headlight bulb. have some one check which headlight bulb is not glowing when you turn on the headlights.

that could be the shorted bulb.

tnx 4 using fixya,

drcool