I bought adigital oil temp gauge from JC Whitney for $36 and 3 senders for $15 each. Along with a 3 pole 3 throw toggle switch (radio shack $4. 95)I can now monitor engine oil,trans,and diff. temps with one gauge,most of the time it's parked on the trans. temp. Gauge seems to be very acurate,when the truck is parked for awhile all three read the same as the outside temp,the range is 0-350 degrees. You didn't say if you had a gauge yet that will determine what type of sender you need,but Ithink any auto parts store can help you out.