Yes like Marg99 said, earths.
I have an issue where my temp and fuel gauges move after the car is off for a minute ST170 dash cluster).
I’m doing my clutch now and other work, the wiring could use some tlc, but I’ll clean the earth points before reassembly to try to fix it before I have the wiring checked, got some basic test tools but I’d rather get a professional.
A autoelec will save you time. A guy I used did his own tuning and was great at diagnosis.
I jammed my
ECU up-loading software from a bluefin flash tune dongle.
I didn’t know the battery needed +12 volts when doing this. Bluefin in the UK didn’t support an old product and nothing online helped, after a week of futile research I called a company at Thornton NSW who had a workshop and mobile sparkys.
The car was running in 20 mins.
My plan otherwise was to get new computers with a new
ECU tune.
Some wiring goes into deep dark recesses so they can use methods to diagnose that are easy.
Id definitely have a go at the earths, plenty of stuff on YouTube if you are unsure and there are safety/airbag precautions you need to take. (Unless you want to put on a cool Momo steering wheel and have a second glovebox where the passenger airbag used to be!)
Good luck, a decent Focus is worth the trouble.
Are you enjoying the handling/steering of the Focus LR?