I have a 2006 and have had no electrical problems whatsoever. As JFought stated, the turn signal problems are caused by a problem in the multi-function switch, I received a letter from Dodge and was told that they extended the warranty on that switch to 150K miles. If I have any problems I will be getting it replaced via that warranty extention.
The problems with the trailer wiring do go to the TIPM, and yes, it is an expensive problem to solve, you can get it reset 3 times, then you will be looking at replacing it. Most people do not realize that they should have had its amps set higher than what the setting coming out of the factory is - total out of factory is 12 amps. You can have it set to 20 amps. You should also realize that many caused their own problems with bad trailer wiring/old trailer wiring/ or improperly installed trailer wiring connections. You should always check to make sure that your trailer is wired to the 'standard' before plugging a trailer in and expecting everything to be ok.
There IS a fellow selling a unit to protect the tpim, I have one, it is doing a fine job, well worth the investment for sure. Years ago people had an aux, relay driven trailer wiring setup installed on all tow vehicles, it was made obsolete when truck manufacturers started offering tow packages on trucks.
If you are serious about buying th truck from your friend, first have him go get the warranty replacement multi-function switch installed, and second, while he is at a dealership, have them fix/reset the TIPM, if after he has taken care of these things and you have no other concerns, then guy the truck. Make sure he does not use the trailer plug after getting the tipm reset. Once you purchase the truck, I would strongly advise you to install some protection for the tipm. After that, happy driving . .
CD