Troubleshooting step 3
What you can check without removing the Speedometer.
1. Ground, Check using test light connect to (+) on battery or a DVM on the Ohms range.
...a. Check ground on dash between (-) on the battery and dash
...b. Check ground on Speedometer housing between housing and dash or (-) on battery.
.......1. Good Ground
...... 2. Bad ground
2. Power
...a. Make sure power connector is still connected.
...b. Touch nut on "I" terminal to see if plug is making good contact with the terminal.
3. Resistance check. Turn power OFF Disconnect all wires on Fuel and Temp gauges
...a. Check resistance from "I" to housing. It should read around 50 ohms
...... 1. If it reads no resistance or infinit then it could be the heater is broken. You would have to replace the gauge.
...... 2. If it reads around 0 ohms, check that the gauge is centered in the housing and is not shorting out. You probably have been replacing fuses at this point.
...b. Check resistance from "A" to housing. It should read around 50 ohms.
...... 1. If it reads no resistance or infinit but "I" to reads 50 ohms then it could be the points are dirty. If you take the speedometer apart, you might be able to clean the points.
...... 2. If it reads around 0 ohms, check that the gauge is centered in the housing and is not shorting out. You probably have been replacing fuses at this point.
...c. Check resistance from "I" to "A". It should read around 0 ohms +0.2 ohms
...... 1.If it does not read around 0 ohms, it could be the points are dirty. If you take the speedometer apart, you might be able to clean the points.
Next step is remove front glass and trim ring of the speedometer housing.
1. Check case of speedometer to case of gauge is 0 ohms.
.... a. If it is not around 0 ohms then the speedometer housing may be rusty and the ground contact on the gauge is not making good contact. Try cleaning up the rust and scrape the contacts on the gauge and test again if the fuel gauge housing is making good contact with the speedometer housing.