Since the plugs are the same on the two different relays and since the one from the breakers clicks in all the right places when I test it, I am hopeful that it will make my car run. The guy at the breakers said the cars were both runners when they arrived.

However, if it does make my car run, can you think of any reason why it might be a bad idea to leave it in car as a permanent replacement?

I spoke to my Hond a dealer today and gave him the details of my car and one of those I found at the breakers. His computer told him that the main relays of these two cars is different. He gave me the part numbers:
My car: 39400-S84 003
Breaker's car: 39400-S1A G010

He said the "39400" bit referred to the product type, ie relay.
The next bit meant body type, "s84" means coupe; "S1A" means 3 door saloon
He didn't know what the "003" or "G010" bit meant though.

I didn't have the chance to play with it last night - my first day back at work after nearly 3 weeks leave was pretty hectic and I got home late. I'l ltry to make time to fiddle tonight.

I examined my broken relay very carefully at the weekend and I couldn't see any bad contacts. I used a test meter to check for continuity between all the pins that were connected to the same tracks, and they gave a good result. In other words, I can't see how resoldering it would make any difference.

 

The typical failure is porosity & microscopic cracks in the solder. Not real easy to see. Something about soldering at lower temperature in the factory. That's the COMMON failure, but doesn't guarantee yours has that exact problem.

I don't know how the other relay would be bad as a permanent repair. They seem to do the same job on either car, and the current draw in either case shouldn't be much different. I just don't know for sure whether Honda does anything goofy with electrical equipment being different in Swindon. It's not like your electrons drive on the wrong side of the wire...

The first couple digits of the VIN indicate where the car was built. "1H" would be a USA-built Honda.

 

Had a very hectic week at work and couldn't make the time to look again until today.

Anyway, I've fitted the relay from the other model and it works fine. The fuel pump temporary supply has been removed and it is now powered from its own loom. So problem solved.

I also had a look to see if I could see why the cruise control stopped working. It turns out that the reason it didn't work was because I accidentally left disconnected the plug on the brake pedal! So I've been driving around without brake lights all week! (I removed this plug to give better access to other things).

Thanks everyone for your comments and advice, especially Jim.

 

Cheers!
We all appreciate hearing about the final resolution - & it helps other people who find this thread.