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Is the gas tank full ? that would make the gauge read full.Have you serviced the cable. a drop of oil can cure a gallon of problems.
The fuel gauge probably has an open somewhere in the sender circuit. With the ignition switched on, jump the fuel gauge sender pin directly to ground. The gauge should rapidly drop to Empty. Check the PCB-to-gauge connections and the I/P cluster harness-to-PCB connections. Burnish the copper foil and terminals at the points of electrical contact using a soft rubber eraser, if necessary. But be careful not to peel the foil away from the plastic substrate; it's an easy mistake to make.Now is a great time to lube the speedometer cable! Make sure the cable is fully seated onto the back of the speedometer head. When you stated that you "used a drill to turn the speedo and it moves like it should," was that with the drill motor attached at the transmission end of the cable? It is very rare for the speedometer drive gear to fail without causing visible wear of the driven gear. However, the drive gear may have shifted axially on the output shaft of the transmission if its retaining clip failed or was not properly installed during prior assembly. Peruse the article, "Common causes of 'bouncy' speedometer needles" for additional insight.
I tested it in the tank and out the tank. ... I know the gage will go to full because if the wires are disconnected it defaults to full. ...
Quote from: Jimartina on May 08, 2024, 12:49:17 PMI tested it in the tank and out the tank. ... I know the gage will go to full because if the wires are disconnected it defaults to full. ...When the gauge wire is disconnected from the sender with the ignition switched ON, the fuel gauge needle should swing well past FULL to the 3:00 o'clock position. When you ground the sender wire the gauge should quickly drop to EMPTY.You can also perform a rudimentary check on the sending unit if you have a decent ohmmeter. With the sender float in its lowest position (EMPTY) an ohmmeter with its leads clipped to the sending unit frame and sender wire pin terminal should indicate ~0 Ohm. Moving the float to its highest position (FULL) the ohmmeter should indicate ~90 Ohms; midway (1/2 Tank) it should indicate ~45 Ohms.If the sender float is closed cell nitrophyl foam, give it a firm squeeze between your finger and thumb nail. If the float oozes fuel when squeezed, the float is saturated and the sender should be replaced with another brand that uses better quality materials.
Might need to test it with sender out of the tank. Use some jumper wires between sender terminals and Truck harness and move sending unit arm up and down. Should tell you if it's dash gauge or not.
When the gauge wire is disconnected from the sender with the ignition switched ON, the fuel gauge needle should swing WELL PAST FULL TO THE 3:00 O'CLOCK POSITION. When you ground the sender wire the gauge should quickly drop to EMPTY.