Classic/Antique Car Repair: temperature sending problem, New Temp sender wont work.

Question
i have a 1977 jeep cj7 with a 304 engine. my temp guage was not working when i bought the jeep. i bought a new sending unit standard part number (TS37) and also purchased an after market guage, when i hook everything up, it maxes both the factory and aftermarket guages out. so i figured i got a bad sending unit, so i purchased another new one same standard part number TS37. i noticed on the old one the top plastic part is black and the new ones are white. is there some sort of resistance problem with the new sender or is this even the right part number. any info you can give me would be appreciated.sida

Answer
My book shows NAPA TS6713SB for that vehicle.

If you have a store which carries Niehoff parts, they show TS82791 for that vehicle.  Kragen and O'Reilly carry them, amongst other stores.

Make sure the wire that runs from the sender to the dash unit isn't rubbed bare or touching something, or broken inside the insulation where you can't see it.  To check for that, temporarily disconnect that wire at both ends and run a separate wire direct from the sender to the dash unit - if that makes it work right, you know your problem is in the wiring, not the dash unit or the sender.

Dick