#2 is the single wire for the temp switch for the idiot light in the dash.
#3 is the 2-wire temp sensor providing actual coolant temp to ECM.
The "ROCKAUTO.COM" text Dan noted in post #2 is a link to the specific temp sensors/switches for hot air's.
You could pick a Standard Motor Products TS66 for the temp switch and a SMP TX3 for the temp sensor.
Keep in mind that the SMP, Wells (WVE), NTK, AC Delco, and GM Genuine are most likely(like Ivory soap - 99and 44/100) the same part as pictured, built in the same factory, just in different brand packaging and price points.
I see you're working with a print copy of the service manual. to help you find parts in the future, bookmark the following link to the exploded parts diagrams for the car found at webautocats. From the home page and the drop down menu at top, you'll find a lot of different car manufacturers and models.
The Buick Regal exploded parts diagrams (AKA 44W crash book) is found via link below.
Genuine auto parts catalogs (BMW, Mini, Rolls-Royce), ETKA (Audi, Seat, Skoda, VW), PET(Porsche), EPC (Mercedes, Smart, Buick, Cadillac, Chevrolet, GMC, Hummer, Oldsmobile, Pontiac, Saab, Saturn).
webautocats.com
Also, if the temp switch and temp sensor are currently working. you might just let them be. BUT, I would pick up a spare for each as these cars are nearly 40 years old and as a result, even some of the aftermarket support parts are drying up. So, if you do remove and replace these, keep the old parts.
if you decide to purchase these parts from RockAuto, remember to go to the website retailmenot.com, type in rockauto in the search bar, to retrieve a 5% off discount code. paste the discount code in the rockauto website sidebar window or cart on the line " how did you hear about us" and press enter. 5% is deducted from your total. codes from retailmenot are always available.
