relay, two 7 wire data devices

I have the need to switch between two devices that each have 7 wires. One of these two devices sends voltage data to a computer. When switched the alternate device will send data to the computer. The relay should be fast enough that the computer does not notice any lapse in the data and the relay should be activated to switch between the devices by a 12 volt signal that will be constant either on or off. What is the part number for this relay and where may I purchase it?

I doubt that you would have to switch 7 wires (unless it's an old parallel interface), and I doubt that "a relay fast enough" is the answer. Relays are very slow compared to computer comms (even at 300 baud), and most comms are not a mere case of switching - parity is often involved if not packet checksums etc. Chances are that you can parallel both streams and toggle the respective enable lines. What protocol is it, and what sort of data?

Well, perhaps some more information will help. The data is 0-12 volts analog. There are three pair that come from rheostats that measure movement and a single wire that lets the device become active. There are three so that the computer can compare them and be sure they agree; if not, the computer declares a fail safe mode. I want to use two of these devices and be able to move from one to the other if a fail safe mode occurs. Thanks.

Ah - now I see the OP voltage data. I missed that analog detail... My apologies! Being rheostats I'd assume low impedance so that contact resistance is not an issue (besides, voltage sensing is high impedance). And I assume there is no common... Most would probably use local isolated ADCs or multi-channel ADCs (albethey usually with a common or ground. Post Edit 9Mar12: - the common (GND) may not be correct, eg, PICAXEs have programmable lower (GND) voltage references. It may be the same for more modern ADCs than I once used. end Post Edit. But recently I saw a "cheap" DIY battery-string monitor based on PICAXEs - all isolated with isolated data comms (and I'd assume at least 10-bit since that's the minimum resolution required for battery monitoring). Can two 4PDT relays be used? They are reasonably common. Alas I too would have to search for an 8PDT - they might not be that common given that telcos etc now use packet switching, though solid-state switches may be a possibility... Was it the 4066 CMOS switch that was popular and they, or similar, might still be used in domestic entertainment units for source switching?

Yes, I see no reason why two 4 line relays could not work. What do you suggest? Thanks, David

5A 4PDT relays are listed in my local catalogs - namely cat nos SY4009 $9.95 (12V, 180Ω) + SY4004 DIN or SY4064 cradle bases (~$5) from Jaycar, & S4290 $7.95 PCB mounting (12V, 160Ω) from Altronics. That's Downunder and in $AUD. I'd expect Digikey etc to have similar. PS - I'm not "recommending", I'm merely FYIing. And I found no specs on switching times...