I need to automatically terminate RS-485 (produced by '51 derivative) and so far has only come up with using Jacks to mechanically connect the termination when pulled.

It would allow me to use better connectors if the termination could be broken by shorting two pins in the plug.

I have searched analog switches, but none I have found would terminate AC with a tolerance of less than, say, 10 ohms. All proudly announce the small differences between the switches in a package, but that does not help me since a) the two ends are not in the same package and b) matching is impossible (a year from now one end may be replaced)

I have considered a relay, but that solution is unattractive since my environment (busses) shakes rattles and rolls.

Any suggestions?

Erik