Light Wiring problem

I am having some problems with the tail lights on my truck. I have no running lights, no reverse lights, and when the right signal flashes, so does the running light on the left side.
The 'TAIL' fuse was blown so I put in a new one...it pops as soon as I turn the headlights on.
I checked the taillight grounds on the rear crossmember and they are connected. Not sure where else to look.
I also have no instrument panel lights anymore. Not sure if that is related or a seperate issue.
Anything in particular i should look at to start with?

Wiring for rear electrics runs out the bottom of the cab on passenger side,check the harness and be sure there is not a wire rubbing and shorting everything out. BJ

check the wire behind the radio the illumination wire which is red/black stripe, that could be a problem....there seems to be a dead short in the wiring, unplug the tail lights and the front corner lights and check to see if it pops another fuse, there could be a pinch in the wireing, when u turn on the signal it might be shorted to the running light wire , check your wiring starting from the tail lights and work your way up

Hmm I may have used that wire as a ground for my stereo. I guess that could be causing that problem. It tested as a ground though and my deck is working fine.

Does anyone know which wires are which for installing a deck in these trucks? I just used a test light to find the ignition power, constant power and what I thought was a ground..then trial and errored the speakers. Maybe I messed soemthing up? Although the tails were messed before I put the stereo in..the dash lights did work before though.

OK well I re did the stereo ground and the dash lights work again and the tail fuse doesnt pop anymore. But the tail lights are still a mess. I'm gonna check out some of those other things tonight i guess.

ya there is no ground wire on the mazdas for a radio jus put it to and piece of steel on the truck, good thing u found the prob,

as for the tail lights check the plugs at the taillights they might be dirty and/or rusty, pull the tail light out and turn on the lights and turn signal and wiggle the harness and pull it out and back in, that might help