You know, I just remembered something from a past FGF project:

You can run a wire from one temp "sender" to the water temp guage, and then another wire from another temp "switch" to the idiot light. The intake manifold has a few bores to allow for both the switch and the sender. Very easy to do and quite inexpensive, just make sure "switch" wire goes to light, and "sender" wire goes to guage.

Quite a few folks have this setup for redundancy, because some don't watch the temp guage as much as I do! They prefer a guage AND a big red idiot light as back-up.