2006 Taurus electrical issue

Car ran fine till last night when a "Check Transmission" message appeared on the dash. Then this morning it was hard to start and idled poorly, wouldn't shift gears properly and the check engine light was on. Auto parts store checked for error codes and said that over 50 codes were reported across every system. Took it to a local auto shop for a diagnostic and after going through it they said it looked like a short in a wiring harness somewhere. They said that tracking it down was beyond them and to take it to a dealer or electrical shop. I asked if it could be the PCM and they said it's unlikely that a bad PCM would throw so many codes.


I'm hoping that somebody out there might have some suggestions on where to start looking for what is causing this.

Can you better describe the symptom of "hard to start?" Did it crank a long time before firing? Did it sputter while cranking but just not start for several revolutions? Did it sound labored in trying to start?

The first thing I'd check is the condition of the battery, the connections to the battery, and all the fuses in the underhood fuse/relay box. If the battery is over 3 years old it would be especially suspect. The electrical systems in newer cars are quite susceptible to brownouts and when starting the car there is a large current draw on the battery. If the system voltage is dropping much below 10.5 volts or so when trying to start the engine, the engine controls can do some unpredictable things.

-Rod