If you're talking about the one on your head (under the temperature sender) then I wouldn't worry about it. That switch's purpose in life is to prevent your OD from engaging when engine temps are under 140° F. The worst thing that can happen with that disconnected is your OD will work when your engine is cold. I'm not sure why this is a bad thing, but I've disconnected that switch on all my driving vans as that temperature port is more valuable for other things (like cooling fan t-stat, aftermarket temperature gauge, temperature warning system, etc). Anyhow, I've put many thousands of miles on my vans without any transmission issues, so I think it's safe to leave it disconnected. If you really want to hook it back up, I would probably go to a salvage yard. Even if they don't have vans, I'm guessing other Toyotas from that era will likely use it too. Tim