Hi Les, then I assume that you need something like this harness with JR/Hitec male & female plug/socket. This one also has a third plug for connecting the battery to a charger when the switch is in the off position.
DON'T use this feature if you are using a LiPo battery!!
There are several other versions without this third plug available here
http://www.componentshop.co.uk/futaba-charging-switch-harness.html

I guess the RX battery is a fairly small NiMH and also has the JR type plug.
BTW: something to check before switching on-
Does your speed controller have a BEC circuit? if so it supplies the RX as well so you don't need an RX battery at all.
Or doesn't your yacht have any auxiliary motor and ESC?
Happy sailing, Cheers Doug 😎
Looking forward to the video of the insulting tape 😁😉 or is that what I keep seeing on the news with Mr T??

Ah insulting Tape. LOL. That's for Donald Trump. I think I may have ordered the wrong switch fitting. I thought they were all the same. But the one I received does not fit the receiver, its a tad too fat. Perhaps I can return it for the correct fitting. Problem is I not at all versed in the various pugs types and associated names for them.

You have been courageous in stopping me kill this little bit of apparatus. Not wishing to waste my time on this murder, I applied two new transfers to the little Proboat Westward 18 in preparation for its initial sail. I have three ponds I can go to, Knightswood Boat Club, Elderpark Boat Club and Richmond Park Boat Club. All within fifteen minutes drive of me. The suspense is killing me. Thanks again.

Hi Les, if you can't solder DON'T CUT ANYTHING! How would you want to connect the switch anyway?
What you need is this
http://www.componentshop.co.uk/jst-male-female-with-on-off-switch.html
I don't recommend insulating tape for anything on a model boat! After a while the glue leaches out and makes everything sticky 😡 --> Emergency repairs only !
If you do cut wires and insert a switch Colin is quite right; soldering and heat shrink sleeve is the way to do it. Wire at least same thickness as the original. You would only need to cut the red wire anyway.
But much easier to use the switch above and the existing plugs. Don't cost the earth.😉
Cheers Doug 😎
PS What a difference one little letter can make! Would love to hear what 'insulting' tape has to say for itself 😉

Very likely to give you migraine. visit your local model shop or look online for the correct switch harness to match your radio gear, that way the plugs will match.

You would be better to solder and cover with shrink tube that would ensure problem free running. As to wire try to keep as near to original as possible. Good day Colin.