Yet another electrickery question.

Two battery set up, starter circuit works fine.

Red bit of electric string goes from the battery to the isolation
switch. from whcih bit of wire go to the charging relay thing and up
the loom into the sidtribution panel. Black bit of electric string
comes back down the loom and currently (if you'll pardon the pun)
wafts about in the engine bay.

I am pretty sure this is the negative bit of string because nothing
on the domestic front works - I assume the engineer disconnected this
while playing with the engine. Question: does this go straight onto
the negative terminal of thebattery or should it be attached to an
earth point anywhere else, and does it matter?

I can always ask the engineer if he remembers what he took it off
from, but thought I'd ask you first so I don't look a total idiot
(except to you, but you're used to me...)
Arthur Marshall
nb Lord Byron's Maggot
.