Array of electrical issues!

[Cameron_Skaats]

2015 GMC Sierra 1500 SLT 5.3
Started having loss of EPS issues exactly replicating the recall, but the software has already been updated from the recall. Now I'm having a wide array of problems: Service Stabilitrac, park assist disabled, traction control turned itself back on, airbag dash light, random flashing CEL, radio screen going black and sometimes cutting audio.
Measured battery voltage today, 12.5 off, 14.6 running, however the negative cable was a tiny bit loose. Tightened that up and now I'm going to buy a new battery as the current one is 4y and 4mo old. If this doesn't fix my issues what kind of electrical problems do I need to dig into? Thanks :)

[mikeyk101]

Many times electrical issues are related to bad grounds. I know you said the negative battery terminal was loose but it could also be a problem in that negative wire. Also make sure to check the G218 ground under the left dash speaker. Sometimes the insulation around that stud needs to be trimmed back so it gets a solid connection. Another is a ground wire on right side of frame just behind front passenger wheel may need to be removed and mounting spot cleaned up then reattached. And finally, there is a ground strap from engine to firewall just off center to drivers side that gets corroded and may need to be replaced as it is subject to corrosion. All these are pretty easy to check and fix if needed. This may be what you need to fix the problems.