On my 90 325I, the fuse gets corroded. I have to clean out the connection every now and again in the fuse box under the hood.
The gears in the speedometer are stripped. If the odometer is working then you have input.
Probably the cheap black plastic odometer gears(2) if you have set in center. If you have odometer on the left and trip odometer on the right then it is two sets...four gears. Usually when one breaks the other is not far behind in the two set type. There are several online suppliers who can provide parts for the repair.
If the speedometer doesn't work either, then the cable broke or came loose. Otherwise, the gears in the odometer broke.
If you open the odometer, there are two small plastic gears. One is connected to the speedometer, the other to the odometer. The speedometer gear drives the odometer gear. In all likelihood, one of these gears is missing a few teeth. I have the same problem with my Ramcharger, same year.
There is a pair of gears driven off the Speedo cable. One or both of the gears have most likely broken. I have a set on the way. Sorry, haven't changed them yet, so I can't give you details on how-to yet.
If the instrument cluster is just mechanical then you will need to pull it out and check that the gears and rod that connect to the odometer are working and still connected and if they are then you will need to have the cluster overhauled by a certified speedometer shop........
The issue with the odometer not working while the speedometer functions correctly in your 1991 Dodge truck is likely due to a problem with the odometer's internal gears or the odometer drive assembly. These components can wear out or become damaged over time, affecting the odometer's ability to record mileage. Additionally, a malfunctioning speed sensor or wiring issue may also contribute to this problem, though it's less common when the speedometer is still operational. Checking the odometer gears and connections may help identify the exact cause.
Replace the speedo head assembly. It is a sealed unit, with no servicable parts. If the speedometer is working, then the cable and the speedo drive gears are working. The failure must be inside of the speedo head assembly itself.
To fix the odometer on a 1984 Corvette, first, remove the instrument cluster from the dashboard. Check the odometer gears for any signs of wear or breakage, as these are common failure points. If the gears are damaged, they will need to be replaced; you can often find replacement gears online or at auto parts stores. After replacing the gears, reassemble the cluster and reinstall it in the vehicle, ensuring all connections are secure.
The gears inside the odometer broke due to heat and age. You can buy the gears and replace them yourself. Or you can take your car to a place were they work on odometers.
If the odometer and trip meter stop working while the speedometer continues to function, it may indicate a problem with the odometer gears or the connection between the odometer and the vehicle's speed sensor. The speedometer typically relies on a different mechanism, such as a cable or electronic signal, which can remain operational even if the odometer is malfunctioning. Additionally, a blown fuse or issues with the vehicle's electronic control unit could also lead to this discrepancy. It's advisable to have the vehicle inspected by a mechanic to diagnose and resolve the issue.
Lower gears in the rear end means that the wheels will turn more than expected for a given gear and engine rpm, so the odometer will read higher than it should.