My service vehicle soon light is on. what do I need to do if my dashboard lights are off and I have no tail lights except when I use my brakes?

Take it back to the installer.

Headlight switch probably the problem. One circuit is shutting off when the other turns on. If it was a fuse or relay, it would just turn off...

You only need to change the tail light fuse if it is blown. If you haven't checked it already, do that. Those stop/tail bulbs are 2 filament bulbs. One filament is for brake lights, and other filament is for the tail lights. So it is possible to have brake lights and no tails, if the filaments for the tail lights are burned out. But of course, it is unlikely that all the tail lights would be out and all the brake lights still work.

You may need a voltmeter to help solve the problem. It could be a problem in the headlight switch (a problem with the park light function), but is more likely a problem with the Lighting Control Module- or the Body Control Module-whichever your car is equipped with. GM first came out with the LCM, and a year or two later came out with the BCM. Both are mini-computers to control lighting and cabin functions. You would have to use a voltmeter and check things like power in and power out at the BCM of the park lights. You would thus need a wiring diagram to go along with the voltmeter. Those modules are located up under the dash-you can use google to see pictures of them, and maybe find locations.

First, the wires you plucked from the rear lights may be ground wires that corroded and fell out of their termination, or could be secondary wires that provide voltage to your tail parking lights.. and if you touched them to somewhere that had voltage going to it, which it sounds like what happened if sparks flew (or you may have touched a live wire to a ground), you may have sent a voltage spike that blew the dashboard lights out. Did you check all the fuses after the seeing the sparks?? I would suspect that you blew a fuse when that happened. What you need to do is get a volt meter to determine if the loose wires have voltage going to them when the light switch is on, or see if they have continuity to ground.. You say the brake lights work but not the tail lights, so maybe those loose wires either supply voltage to the tail lights, or could be the ground wires for the tail lights. A meter will let you know if they either have voltage going to them or if they have continuity to ground. If you don't know how to do this, you should let someone who knows what they're doing check the wires as you may cause even more damage if you don't know what you're doing.......... I didn't look up your engine codes, but if you have one that has MAP/BAR , it could be that your MAP (manifold absolute pressure) sensor is bad. This will definitely cause the gas mileage to drop and could cause the engine to run bad..You need to have this vehicle checked for vacuum leaks too. Being that it's an older car, you could have cracked hoses or collapsed hoses causing a vacuum leaks which could also trip the MAP/BAR engine code. If your gas mileage is that bad, it sounds to me like the engine could use a good tune up. Replace air filter and PCV valve, plugs/wires etc. Check for bad or dirty sensors, vacuum lines etc need to be checked...You can have the codes cleared from the computer, but once you do that, the computer will just send the same codes and trip the check engine light again if you do not find and fix the problem causing this condition. Even when you repair the problems, the car will need to be driven for a bit before the computer will allow all the emission parameters to reset and then give you the green light to have the car inspected. Simply clearing the codes without fixing the problems will not allow the vehicle to pass an inspection. The computer needs to reset after the repairs have been done, and then you can take it in for an inspection..Sorry I can't be of more help, but this should give you somewhere to start..Have a look at your vacuum lines, clean or replace the MAP and MAF (mass air flow) sensors (there are you tube vid's on how to do this) and get a meter to see if those loose wires have voltage to them or if they have continuity to ground. Then maybe you can figure out where they came from. I suspect they may have pulled out of a rear light wiring harness connector or a light bulb socket. Good luck!

the fuse is labled 'brake'

I would replace the fuse... and then have someone stand to the rear of the vehicle and watch the lights come on as I applied the brake... if the fuse blows again... note which tail light did NOT come on durring this test and replace the bulb.. it is grounding to itself and causing the short.

sounds like wireing is shorted together. you need to trace down wires and check for bad spots in wireing. also be sure and check plug if you are set up for trailer lights.

check the fuses,if that's not it replace the headlight switch

either a stop or turn signal or tail lights are out

it indicates that a light is out on the vehicle possibly the highmount stop light or a headlight

does your vehicle have tilt wheel...that is a common problem and your brake light wires run down through the steering column