HiThese relays are a copy of the Lucas 6RA which was used extensively in English vehicles of the time for example as an overdrive relay for Austin Healey 3000's. Reproduction 6RA relays are available for example at OVERDRIVE RELAY
They are generally very reliable and only need a clean of the contacts but sometimes the coils etc can burn out. Below is a description of how to refurbish a Lucas 6RA which I wrote for an Austin Healey magazine.
"The first step is to carefully bend back the holding tabs which keep the circuit board in place. I find a pair of flat nose pliers is best for this but be careful as too much force or movement will break them. Carefully remove the internals.
Clean the two electrical contacts. I use a small file for this but emery paper would also do. Be careful not to get too vigorous or you will take them out of adjustment. After you have cleaned it all you can check the electrical operation by using a multi meter to check there is little or no resistance across the points when they are closed.
The relay consists of a central coil which creates the relay latching force and a set of contact points to provide power to the horn/lights/overdrive etc.
Using a multimeter you can check that the relay is operating properly. Check that there is continuity in the coil winding W1 to W2. Check continuity from C2 to the contact blade. Close the contacts and you should have continuity from C1 to C2."
While you have the relay apart you can also get the case zinc plated to look like new.