* Main Power Feed: The problem is probably upstream of the fuse box. Check the main power feed wire(s) to the fuse box. These are usually thick wires connected directly to the battery or a main power distribution point. Look for corrosion, broken wires, or loose connections at the battery terminals, the main power cable connection to the chassis, and at the fuse box itself.
* Ignition Switch: A faulty ignition switch could be preventing power from reaching the fuse box. Try wiggling the ignition key while testing for power at the fuses. A failing ignition switch is a common cause for widespread power loss.
* Main Relay (Possibly): While it's a possibility, the main relay is *less likely* than the above issues to cause *complete* power loss to that many circuits. Main relays typically control things like the fuel pump and ignition system, not necessarily the heater blower motor and gauges. If *only* fuel pump and ignition were affected, the main relay would be a top suspect. But the broader nature of the power loss suggests a more fundamental problem.
Troubleshooting Steps:
1. Battery Voltage: Check the battery voltage with a voltmeter. A low or dead battery can cause these symptoms. Try jump-starting the car to eliminate this possibility.
2. Battery Terminals and Cables: Inspect the battery terminals for corrosion and tightness. Clean them thoroughly if necessary. Check the main battery cables for breaks or loose connections, both at the battery and wherever they connect to the chassis.
3. Main Power Feed to Fuse Box: With the key off, locate the main power feed wires going into your fuse box. Use a test light or multimeter to check for voltage at the input side of the fuse box. If there's no voltage here, the problem is upstream.
4. Fuse Box Connections: Carefully examine the connections to the fuse box itself. Look for loose or corroded connectors or any signs of damage.
5. Ignition Switch: If the previous steps yield nothing, suspect the ignition switch. This requires more specialized testing or replacement. A qualified mechanic can test the switch for proper operation.
6. Main Relay (After other checks): Once you've ruled out the more likely culprits (battery, cables, main feed), then check the main relay. Swap it with a known good relay (if possible) to see if the problem is resolved.
Important Safety Note: Disconnect the negative battery terminal before working on any electrical components. Be careful when working near the battery, as it contains corrosive acid.
If you're not comfortable working with car electrical systems, it's best to take your Prelude to a qualified mechanic. Diagnosing electrical problems can be tricky and requires experience.
