92praylude blinkers and brake and marker lights all work until headlights are turned on then all lights blink even licens plate lights blink what is wrong already replaced combanation switch

There should two separate bulbs for marker and blinker. It sounds like a bulb is burnt out, bad ground, melted socket or a wiring anomaly. Are you certain it's supposed to have 57 series dual element bulbs for blinker and markers?

The problem was a bad left front blinker socket that was grounding out

Could be the turn singal relay not getting the correct power when lights engaged. Take out bulb from headlight and then turn on headlights. Now no power to the headlights. Try to turn on blinkers now. If they blink replace signal relay, if they still are solid it may be your flasher. Just a guess without looking. Thanks.

what do you mean by marker lights?

The front park lights work correct? If the front park lights work than there is not a problem with the light switch since the brown wire from the switch supplies power to the front park lights, front side markers, and the rear taillights. There should be twelve volts on the brown wire from the headlight switch with the connector plugged in and the park lights turned on. If this is true that there is a problem with the wiring to the back of the vehicle. A thorough inspection of the harness should reveal the problem. The dim break and blinkers support the above. High resistance also know as corrosion, in the wires or connections would cause this problem.

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Your right rear turn signal bulb is blown.Replace the bulb and the fast blinking will stop.

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make sure our lights at rear are grounded sounds like a bad earth

The headlight power wires are probably touching the taillight power wires.

Generally means that a bulb is out.
When a bulb blows, then the blinker has less electrical resistance, so the blinker works at a faster pace.
Have someone in the car as you inspect all lights.
.... and! As long as you have an assistant, check the headlights, stop lights, license plate light, brake lights, emergency flashers ....