'84 5kS radiator

[Michael Spiers <mikes@specnet.com>]

Went by a boneyard on Saturday to pick up a replacement heater control valve
for the one I blew up on Thursday.  Went to pay for it, the guy tells me I can
have it.  Cool.  "How much for the radiator in the gray '85 5000?"  "Hundred
bucks."  "Thanks."  Last week he wanted $125.  I went home, scraped up $87.97
and headed back up.  Came home with a radiator.  This was an aftermarket
radiator, didn't have a name but it was made in Singapore.  Must have been
replaced three months before the car was junked (not wrecked, the panels were
in perfect shape, damn thing was in better condition than the '84!) because the
radiator was in PERFECT shape.  My question is this:  the radiator I pulled out
has a sensor at the bottom, that has a three prong connector.  My (her,
whatever) '84 has a two prong connector.  I'm just going to take the sensor out
of the '84 and put it in the new radiator, but what is the extra prong for?
 Also, any tips for replacing a radiator?  It only took five minutes to get the
one out of the '85, but it didn't have a grill, a left quarter panel, an
overflow tank, or a hydraulic pump, so it was kinda easy.  Anything I should
watch out for?  TIA for any suggestions.

-Mike
87 5000CS TQ