What would cause the fuel gauge thermostat rpm and speedometer not to work in a 96 grand am se all fuses have been checked only one that was blown lighter how is this repaired?

The fact that the fuel gauge, temperature gauge, RPM gauge, and speedometer are all out simultaneously in your 1996 Pontiac Grand Am SE, while the other systems (like lights) are working, strongly suggests a problem with the vehicle's electrical system, likely centered around the instrument cluster itself or its power supply. A blown lighter fuse is a red herring and unrelated unless there's a hidden short in that circuit somehow affecting the main power feed.

Here's a breakdown of the likely causes and troubleshooting steps:

1. Instrument Cluster Issues:

* Faulty Instrument Cluster: The most probable cause is a malfunctioning instrument cluster. Internal connections, circuit boards, or the gauges themselves could be failing. This often requires replacement or professional repair. You might find a used cluster online, but make sure it's the right one for your year and model.

* Loose Connections: Check the wiring harness connections at the back of the instrument cluster. Ensure they are securely plugged in. Corrosion or damaged pins are possibilities. Disconnect, inspect, and reconnect them carefully.

2. Power Supply Problems:

* Ignition Switch: A failing ignition switch might not provide the correct power to the instrument cluster. This is less likely if other electrical systems (lights, etc.) work correctly.

* Wiring Harness: Damaged or corroded wiring between the ignition switch, the instrument cluster, and the engine's sensor(s) is a possibility. This is a more involved diagnosis requiring tracing the wiring harness. Look for breaks, chafing, or corrosion, particularly near the steering column and under the dash.

* Power/Ground Issues: Check the main power and ground connections for the instrument cluster. A loose or corroded ground is a common culprit for multiple gauge failures. These connections are often located near the instrument cluster itself.

3. ECM/PCM (Engine Control Module/Powertrain Control Module): While less likely given your description, a fault within the ECM could interfere with the signals sent to the gauges. This would require diagnostic scans using an OBD-II code reader.

Troubleshooting Steps:

1. Re-check all fuses, even the smaller ones: Though you say you've checked fuses, double-check *every* fuse, even those that aren't obviously related. Look for any that are weak or show signs of discoloration.

2. Inspect the wiring harness: Carefully examine the wiring harness going to and from the instrument cluster. Look for any visible damage or corrosion.

3. Check the ground connections: Locate the ground connections for the instrument cluster and ensure they are clean and tight.

4. Test the instrument cluster (advanced): This requires some electrical knowledge and testing equipment. You could try to find someone with experience, or a repair shop. Testing voltage at the connector pins feeding the cluster could pinpoint the problem.

5. OBD-II Scan: Get a diagnostic code scan from an auto parts store or mechanic. While unlikely to pinpoint the gauge issue directly, it might reveal other problems that indirectly affect the gauges.

Important Note: If you're not comfortable working with car electrical systems, it's best to take your Grand Am to a qualified mechanic. Improperly handling the car's electrical system can cause further damage. Replacing the instrument cluster is likely the easiest (but not cheapest) fix if the wiring and power are found to be okay.