What may cause issues across multiple systems?

New contributor, welcome.

And yes, this stuff can be frustrating. How many miles on the car's odometer? Was this a salvage title, Florida or Gulf Coast flood car? Did you personally check the cars Vehicle Identification Number (VIN) repair/title history?

In repairing cars (or solving any problem) you can solve things in a combination of three factors.

1. Effort
2. Time
3. Money

Welcome to life. We have no clue what's wrong with your car. Could be anything.

By the way, at first three glances to your description of the issue, that sounds like a really bad ground to sheet metal somewhere in your system. I'd guess there are probably eight or ten grounds located in your car. You should really obtain a complete wiring diagram (Chilton/Haynes) or the Electrical Vacuum Troubleshooting Manual (EVTM) from Ford for your vehicle. Those should show you the colors of all the wires, and all the ground locations in the vehicle. The EVTM is better if you can find a copy, but it might be more $$. I will say, this does NOT sound like a systemic issue with 2003 Ford Taurus. It does sound a whole lot like complaints I'd expect from a flood state/ salvage title car.

And many of us here have worked on lots of different cars solving electrical and related troubles. I know I have. And without a doubt the most troublesome, time spending repairs leave the strongest memories for us. I've seen pinouts, cut wires, burnt wires, burnt insulation with wiring intact, and open circuits within a single power distribution copper buss system with riveted connections. I've seen water on Transistor to Transistor Logic (TTL) 5 volt sensor systems used throughout, and that causes HUGE intermittent troubles in sensors and within connectors. I've seen overheated parts burn out. And all that stuff hurts. Lots of those failures were intermittent. I've seen wiring diagrams from the factory with hardshell connectors wired in mirror image. Ugh. I've worked on new cars, preproduction cars and used cars. All of the above.

Me, I spend time to train myself, learn how stuff works, and do careful troubleshooting with a Volt Ohm multimeter. You are certainly invited to so the same. Its not really expensive. You need to understand basic electricity concepts. Learn how to read voltage. Learn how to read electrical resistance.

The alternative is to pay someone to do that for you. In troubleshooting electrical systems you can spend hours identifying the source of the problem, and when you figure out exactly what it is, it may be a ten minute fix. Stuff happens.

Assuming you don't have a flood car with salvage title, any problem you come up with can be fixed. It make take ten hours to find the problem, but don't give up. And if you don't like that system, you should buy a new car, purchase a repair warranty and move on. Treat your car well, change oil regularly and it will last a whole long time.

Question for you. What is your expectation of the life of your 2003 Model Year Taurus? My guess, is that car, well maintained, should last around 180,000 to 220,000 miles or so (not accounting for corrosion in Rust belt states...)

First thing I would check when you are experiencing any of these symptoms is the battery voltage. Check it at the battery terminals and at other places, for example the cigarette lighter socket. If the voltage is below 13v with the engine running, you may have a bad connection between the battery and the fuse box or between the battery and the body. A faulty alternator or a bad connection to the alternator can also cause issues like this.

Start by checking simple things like these then report back for further help.