No lights in dash gauges/taillights fuse popping

[mccula]

So for awhile, the dash gauge lights were funky... they'd come on, go off, blink, fade, etc. whenever they wanted too. Now, the tail light fuse will pop... I thought it had to do with the headlight switch as it seemed to be affected by dimming/brightening the switch. So I bought a new switch, put it in, put in a new tail light fuse, and tried to turn on the headlights. Turned em on, then I get a small spark from the headlight switch and the fuse for the tail lights pops again. No dash lights at all. No idea what's going on... no visible issues with the wiring going back to the brake/tail lights, but I haven't totally unwrapped the wires there either.
I'm stumped. Any ideas?
Edit: Sorry, forgot to mention it's a 70 dart. Was a 225ci car now a 340. Has been a 340 since we've owned it.

 

[RedFish]

Could be any lamp in the circuit blowing the fuse. Includes, park lamps, tag lamp, radio, shift indicator, ash tray.

 

[mccula]

Do you mean the actual lamps or the wiring and other related electrical components?

 

[Snake]

Door jamb switch could do it to.

 

[RedFish]

Do you mean the actual lamps or the wiring and other related electrical components?

Ofcourse any pinched wire could be the cause. I was only pointing out the many items on the same fuse. Bulbs and bulb sockets are where I start searching unless there is a aftermarket radio

 

[cudajim]

Using the term "pinched wire" really means a wire inadvertently shorting to ground or to another wire. I agree that starting at the bulbs and sockets is likely then move on to switches etc.