* Alternator: A failing alternator won't produce sufficient voltage. All three systems (cruise control, AC, and transaxle – especially the electronic controls within it) require electricity to function. A weak or failing alternator can lead to low voltage across the board, causing them to shut down. Check the alternator's output voltage while the engine is running.
* Battery: A weak or dead battery could also lead to insufficient power for these systems. While less likely to cause all three to fail simultaneously than a failing alternator, it's still a possibility. Test the battery voltage.
* Fuses/Circuit Breakers: Though less probable for all three to fail at once, a main fuse or circuit breaker could be blown, cutting power to multiple systems. Check all fuses and circuit breakers related to these systems in the fuse box(es) – there are often multiple fuse boxes in a car this age.
* Battery Cables: Corroded or loose battery cables can impede the flow of electricity. Check the connections at both the battery and the starter motor for corrosion and tightness.
* Main Power Wiring Harness: This is the less likely but most serious possibility. Damage to the main power wiring harness (perhaps from a rodent infestation, corrosion, or physical damage) could interrupt power to multiple systems. This requires a thorough visual inspection of the wiring harness, which can be a complex task.
* Body Control Module (BCM) / Powertrain Control Module (PCM): These modules control various aspects of the car's electrical and mechanical functions. A failure in either (or both) could theoretically cause all three systems to malfunction. Diagnosing a BCM/PCM failure requires specialized tools and expertise.
Troubleshooting Steps:
1. Check the battery voltage: Is it within the normal range (around 12.6V when not running, and 13.5-14.5V when running)?
2. Check all fuses and circuit breakers: Replace any blown fuses, but be sure to find out *why* they blew before replacing them.
3. Inspect battery cables: Look for corrosion and ensure tight connections.
4. Check the alternator's output voltage: Should be within the range mentioned above when the engine is running.
5. Visual inspection of wiring harnesses: Look for obvious signs of damage, such as fraying, corrosion, or rodent gnawing.
Important Note: If you are not comfortable working on car electrical systems, take your Cadillac to a qualified mechanic. Improperly diagnosing and repairing electrical issues can lead to further damage or even injury. The BCM/PCM are complex components; trying to fix them without proper knowledge can be disastrous.
