I'm trying to identify an old apparently RS supplied component marked RS 339
487. It looks like a V3 microswitch. It has an operator button like a V3 microswitch. It has three terminals marked 1-2-3 like a V3 microswitch, but unlike a microswitch nothing is connected to anything ! As there are two of these devices in my hydraulic tool turret, both exhibiting these symptoms I'm wondering if it is something more subtle than a normal contact device - maybe hall effect or optical? The only difference physically from a normal microswitch is that the three contacts all emerge from the short side of the body away from the button, whereas ordinary ones usually have the common sprouting from a long side but bent towards the short side, and the no/nc contacts where mine are
Modern RS part numbers are of the format XXX-YYYY so searching their web site fails to satisfy. (It's in a 1983 vintage machine)
AWEM