I own a 2002 mercury grand marquis. It has 100,000 miles on it and is an automatic transmission.

Over the past year the signal light when I have made turns has been flashing too rapidly. Then about a day or so after this the dash lights will come on,(as in all of them), and the car will stall while driving. I have replaced the fuel system, the alternator, the engine, and no one can seem to fix this. I have been to various repair shops in my area and while things have been fixed and/or replaced the issues persist. 

It would not be a big deal but this happens when driving and it is dangerous stalling on the road in traffic. Various repair shops have hooked it up to a diagnostic machine but have not been able to fix it. Any ideas?