OH NO! WD40 leaves an insulating film after drying. On a ship, one of my maintainers found out the hard way after spraying the very many relays and switches in several of the communications controle boxes around the ship on open decks. Instant problems! Took a very long time cleaning off each individual contact in all boxes to get it all working properly again.

Location: NW Devon

Coke or Pepsi are just as good.

Once connections/switches cleaned (and after soldering wire) use a Contact Treatment Grease. For example RS components do a 20g syringe container. It may seem a bit expensive but you only smeer a very thin coating on contacts to help prevent corrosion, spark burning and lubricate the contacts. Makes switch action smoother. Also use on battery terminals.
I have had mine for years and still not even used 1/4 of the tube.

Location: NW Devon

We've just used this with great success this morning on our Transit van - half an hour before MOT and the entire instrument panel was dead. Pulled out the pod, found everything behind the dash was pretty sh***y, squirted the plugs and sockets and fuse holders and we were back in business!

Does what it says on the tin!

Location: Herefordshire, with an "E" not a "T".

Location: Shropshire

Ian's cleaner and Derek's protector arrived today and everything is working properly again - many thanks again!