Okay, so I ordered, received and installed a new IVR from Laurel Mountain Mustangs...and the fuel gauge didn't even quiver. Reinstalled the old one, and again it went right up to 1/4 tank. Here is the link: http://www.mustangsunlimited.com/search_sorted.asp?Keywords=instrument+voltage+regulator&x=28&y=13 It is the 3rd one down, #GR512 01 Is this the right IVR for the 76' Mav to use. It is identical to the OE. HELP!!
Did you try and test the new one with a volt meter? Looking from the back of the cluster, the terminal on the right should read 12volts and the one on the right should read 5volts. It's possible you bought a bad one.
Okay. Here's an update. Installed new IVR, completely cleaned circuit board and used all new bulbs (while I was in there) along with contact grease. Fuel gauge tested fine in dash, and new sender in tank. All wiring in between sender and dash checked fine. Finally I decided to clean and scrub the 2 contact points in the harness that attach to the sending unit at the tank.....TAH DAH...it worked fine! As I figure it, this contact is just like the contact used for trailer lights (4 or 5 pin harnesses). From time to time I've had to take a small, round file and clean inside the female part of the harness and use contact grease to keep corrosion from coming back. Well, that was the issue here as well. Used some good cleaner, then lightly filed the female harness innards, put some contact grease on, and it worked fine. No problems since then.
