Right so I’ve been having issues with my car holding charge. I’ve replaced the entire charging system, new battery- ford. New starter motor and new alternator. The alternator is a Lucas one. But since having them replaced I have run into the same problems. Upon inspection there is a two pin plug going into the alternator as to which there is a purple wire and a black wire. The purple is the live wire reading at 10V and the black is completely dead. Does anybody know why there is 2, if there is meant to be 2 or what else this could be… any help is appreciated. 

TIA

* It’s a mark 8, 2018 Fiesta ST-Line

That sounds like the signal wire which makes the smart charging system smart. What you are reading as 10v is actually a signal wave form. Think of the two wires as positive and negative although they are actually a signal wire and a reference wire for the signal. What you have seems to be correct.

23 minutes ago, pcaouolte said:

That sounds like the signal wire which makes the smart charging system smart. What you are reading as 10v is actually a signal wave form. Think of the two wires as positive and negative although they are actually a signal wire and a reference wire for the signal. What you have seems to be correct.

Any idea why it could be draining then? We’ve tried mostly everything 

How fast is it draining? They all drain over a few weeks, is yours draining faster than that? What are the symptoms when it drains? Do things stop working (which things)? Or does it get so low that it won't start?

4 hours ago, pcaouolte said:

How fast is it draining? They all drain over a few weeks, is yours draining faster than that? What are the symptoms when it drains? Do things stop working (which things)? Or does it get so low that it won't start?

Couple of days. My auto start/stop hasn’t worked since I brought the car. Same with my CarPlay, and I have no tire pressure sensors for some reason. Nothing is plugged in or no lights left on.