Make a signature with year of truck, drive line type, engine size, and other tid bits of info. It'll help us answer your questions.
If you have a late model Ranger with a dummy gauge, replace the sensor. It's a common issue with our Rangers and cold/damp weather. On my 01 w/ 3.0L, the sensor is located on the rear top side of where the tranny mates with the engine block. Look on the passenger side, you won't miss it.
Also to help you out with pics, try the SEARCH button located at the top menu bar. This has been covered many times before with pictures and detailed instructions for replacement.
BTW, welcome to RF!!!
2001 Ranger Edge - Bright Island Blue3.0L/5-Speed Manual/Supercab/Stepside/Sliding Rear Window/Step Bars/31x10.5 BFG All Terrain T/A's on Factory Chrome Rims/Class III Hitch/Black headlights & Corners/Black Tail Lights/Titanium Chrome Corner & Signal Bulbs/Sylvania Silverstar ULTRA Headlights & Fogs/Ventshade Window Vents/Tonneau Cover/14% Tint/Pioneer Deck w/ 2x12" Pioneer Subs & Clarion Amp/MAC Intake/Leather Seat Covers/Bilstein Shocks/Westin Safari Bar with 6" 130W Blue Tint Fogs/2006 Fender Badging/LED 3rd Brake Light
Too much to list, check out my Cardomain
PROUD TO BE CANADIAN