Hyundai Repair: Hyundai Tucson wont start, hyundai tucson, battery cables

Question
In July of 2007 I had Circuit City replace my radio. In November of same year I went out of town, car sat for 2 days, when I returned the car wouldn't start. From November to January off and on the car would start. Took it to the dealer, they said it was probably because they hooked the radio directly to the battery and it was draining the battery, after January I had no problems until November of the next year, same exact thing happened, again this was just throughout the winter, again the dealer said it was the radio. November of last year it started again, more frequently, it stopped around February but has started again. Now when ever I turned the car off it wont start. I have removed the fuses to the radio (suggested by someone who installs radios) still the car wont start, the battery has been replaced twice, the alternator has been checked, no problems. Now my warranty has expired, the dealer is saying I would have to have an electrician check the car and this is very costly.  Do you have any suggestions on what the problem could be or where I should start?

Answer
If you turn the car off, immediately try to restart it, and you find it will not start, then the radio is *not* the issue for this particular symptom.  In this case, presuming the engine does not crank, you'll need to check the battery (for amount of charge), starter, and battery cables.  

A faulty or improperly installed radio could cause a vehicle to not start after it has been left sitting (not running) for a significant period of time.  Several components in your vehicle (radio, computers, clock, etc.) need to use a small amount of power to retain their memory or perform certain functions even though the car is off.  If the power used is too great, it can discharge the battery if the car is left off for too long.  How long a period of time this is depends on the battery, the condition of the battery, and the amount of current actually flowing.  

It's a relatively simple matter to check whether the radio is the issue.  Using an ammeter, check the amount of current (called parasitic draw) flowing when the car is off (this should be less than 50mA, but even at 100mA, there's probably little danger of an issue).  Then, disconnect the radio and check again.  The difference between the two currents will be the amount used by the radio, and you can then determine whether the radio is causing your problem.  

If you do have excessive parasitic draw, finding the specific problem is typcally a little more difficult than checking one item.  (Of course, if you have reason to suspect a particular item, such as the radio, there's no reason you cannot disconnect it and recheck as I've described above).  The most efficient way of locating the excessive parasitic draw is typically to remove fuses one-by-one from the underhood fuse block until the excessive draw disappears.  Then, one can check all the circuits that fuse powers and so on until the problem is narrowed down to one item.  This can be quite a time-consuming process, especially if the person doing the work is not good with electrical work.