2 12V sources going to the same connection will yield 24V at that spot.
The relays should be one way, so that there is no chance of feedback frying the ECU.

Having the fan on does cool the engine a bit, but not very much.
An electric water pump would very much be the way to go.

Frank McCoy aka Mod-deth aka Mid Life Crisis aka SVT Doood aka mcgainer is a SCAM ARTIST Pre98 Zetec - Some Mods