Speaking of grounds....My wife bought new in '05 a ford focus that I have had the misfortune to upkeep for her.lol
It's not that bad or maybe I'm used to it ....idk... but I have to clean cables and even added a ground because it would idle down with electrical load....like fans switching on or lights and heater blower going. Added an 8 gauge ground wire to the fender about 3 weeks ago and it went smooth....no idle change, did the mounts for the 7th or 8th time too..notorious on those to go out. Now 3 weeks later...I have to clean and re tighten the grounds ,again. We live by the beach..... but for some reason, only the focus has that problem. Grounds and signal wire isolated from eachother and other wiring IS most important.
