Difference between red & black relay

[rw7810]

Ok, gents, I think I used to know this, but what is the difference between the red and black round relays used on early models ?

[timmy2]

Red ones have a back feed diode to stop it from re-striking on a collapsing field, black ones do not.

[Arne2]

So red could generally be used to replace black, but not vice-versa?

[timmy2]

To Arne, yes.
It’s really only the collapsing field of the fuel pump motor that is a concern. Wouldn’t want it to fire back up when turning the engine off...

[rw7810]

Thanks