Stewart Warner Temp Gauge, Single Wire??

[hotwls13]

I haven't ran the truck for more than 3-5 minutes at a time since I bought it a couple months ago. Mostly because it barely had any gas and I was in the middle of the tank relocation. Now, because I still haven't gone through the running gear (other than changing rear gear oil, checking engine oil, coolant and trans fluid levels).

I'm going to assume my factory Temp gauge doesn't work (since previous owner added a Stewart Warner temp gauge). Temp really hasn't gotten that high (somewhere a bit above 100) but honestly the truck hasn't ran for long and I wasn't watching the temp that closely. I was also worried thermostat could be stuck and cause truck to overheat??

My 2 questions are:

1. What are the chances my original gauge works and just needs a new sender or proper wiring (or both)?

2. The Stewart Warner only has a single large black wire coming out of it. Does that sound right?? And where should that black wire be going??

Thanks,

I'm a newb to all of this, but I'm willing to learn.