2006 ford ranger headlight working, taillights/license plate license NOT

Hello my name is Leo, i am new to diagnosing electrical issues so sorry if these are silly questions.......
I have an 2006 ford ranger fx4, no license plate light or rear lights of any kind.
When i tap the brake, the rear lights will come on but that's it.......(this is a separate circuit i understand???? rigged to the trailer plug for a backup?
The front headlights work, they are getting power from the light switch.
The instrument cluster can not been seen during the night but besides that everything seems functional.......km,speed,rpm, warning lights do work....
I checked the large fuses for the instrument cluster under the hood with a multimeter and they are good.
Any ideas???

I have a cheap knock off power probe i just need direction.....

Applying the brake ONLY. the rear lights come on or both brake and rear lights? If the later do both light brightly/normally?

My first idea from your description is a bad ground.

Make sure you test the supply voltage back at the consumer UNDER LOAD. In your case this would be at the lamp with the circuit on/activated. Do also test for voltage drop on the negative side of the circuit, you may find your problem quickly :.

So neither tail lights or dash illumination work? Do the front parking/side marker lamps work? If not I'd be looking for a fuse as the first step. If the labeling in the fuse boxes is unclear try the owners manual. Should be a free download from Ford if you don't have a treeware copy.

Check Fuse 31, behind right side of dash. If the fuse is good, listen for the Parking Lamp Relay to click when you operate the Parking/headlight switch.

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