1992 ls 400 spedometer started to read slowly,then stoped working alltogether, pointer rests at about 20 mph. is there an easy fix, replace cluster, sensor or what ? thanks

One or more of the illumination bulbs in the cluster may have burnt out. There aren't many, maybe only 3 or 4, so if just one burns out, you won't get much illumination.
You have to get to the back of the cluster to replace them. The hard part is removing the cluster, lots of trim pieces to remove first, then pull the cluster out a little to disconnect the electrical connectors. Then the bulbs are easy to replace-parts stores sell them.

The fuel level indicating system is a magnetic type system, which consists of the sending unit located in the fuel tank, an anti-slosh module located on the back of the instrument cluster, and a fuel gauge located in the instrument cluster. The sending unit changes resistance according to the level of fuel in the fuel tank, which varies the current flow through the gauge.The pointer position varies proportionately to the current flow. In this system, the sending unit resistance is low (22 ohms) when the fuel level is low and high( 145 ohms) when the fuel level is high. The pointer of the magnetic gauge remains in position when the ignition is turned to the Off position. On some models, an anti-slosh module is used to dampen out fluctuating fuel signals from the sender. Some vehicles are equipped with a low fuel warning indicator. The anti-slosh module will also actuate the low fuel indicator when the fuel level in the tank reaches 1/16 to 1/8 full.


Do your other gauges/warning indicators work properly with the ignition on? If not, check for power at the fuse panel/fuses.

If they do then partially remove your cluster with connector still installed and check for voltage at cluster connector and gauge. Check continuity of cluster and gauge for ground.

Sometimes the anti-slosh module (if installed) goes bad in the Grand Marquis but not likely.

Sender troubleshooting:

1. Perform test with resistors as follows:

1. Disconnect wiring connector at sender unit, then connect resistor between gauge lead and a suitable ground.
2. Turn ignition switch to On position.
3. With 145 ohm resistor, the gauge pointer should contact the Full mark.
4. With 22 ohm resistor, the gauge pointer should contact the Empty mark.

1. Perform test with fuel sender of known quality as follows:

1. Turn ignition to Off position.
2. Disconnect wiring connector from sender and connect it to test sender.
3. Move float rod away from fuel filter against Full stop position. Wait approximately 30 seconds, then turn ignition switch to On position. The gauge should read on or above the Full mark.
4. Move float rod toward fuel filter against Empty stop position. Turn ignition switch to Off position. Wait approximately 30 seconds, then turn ignition switch to On position. The gauge should read on or below the Empty mark. If gauge works properly replace sender, which involves dropping fuel tank.
   

Hi!!
Check on the instrument cluster for a switch labeled English/Metric, pressing that switch will change the display back to miles.
Good Day!! A HELPFUL - 4 THUMBS - rating for this solution would be greatly appreciated. Thank you for using FixYa.

Ok, Looks as though your Instrument cluster is FUBARED. Has anyone tried to see if they can get a live reading from the ODB2 port under the dash. If you can get a scan tool to show MPH and RPM's then your cluster is done. Replace it. As for the Alarm system I would lay odds that once you resolve your Instrument cluster issue,rest should comeback online. Good luck and let me know how you make out. Pat

I have worked at a chevrolet dealer for 12 years and have probably replaced a few hundred of these clusters. the speedometer portion of the cluster always goes out, I have had very few speed sensors go out, and when they do the check engine light will come on and the trans. won't shift, if the new cluster is too expensive they are easy to replace if you just buy it outright, you can also get a wrecking yard cluster your miles just won't match

Your instrument is bad, The spiral coil for the needle is alraedy out ot calibration therefore it has been jumping around. Even they reset, it already been stretching. It needs a new one.
Don't waste mony for the reset.
It is probebly expensive from dealer plus labor. Just to check out the price,
You can get a used one from ebay for $85. However, you need to know how to replace it. Let me know it you need any help.
Meanwhile you can gauge your RPM to keep your speed under control on the long trip.For example: 2000 rpm is about 55 mph. Try to keep it below 3000 rpm so you don't get over speed limit.

to fix this you have to remove the instrument cluster, it's not hard (4 screws) and take it apart. On the hidden part of the board, there is about 20 contact points (where the cluster connects) all you have to do is reheat the solder around those pins and add solder accordingly and you'll have an instrument cluster that's good as new

how did you fix it

it will be a new cluster for you. gears in the cluster that is connected to the cable is no good. Replace the cluster and you will be fine.

This happen to me too. Had to get it replaced under my exstended warrenty that cost me the $200 deductable but would of coast over $400 if this happened later.