Used to come on after raining and then go out after a few drives. Now, has remained on. Neighbor hooked a diagnostic computer up to it and it didn't relay any codes. Removed the fuse (fuse 7.5) for 10 seconds and light still remains on. Any other suggestions?

. Test all under-dash fuses with a test light or multimeter:

https://www.askmehelpdesk.com/cars-trucks/faq-how-troubleshoot-repair-maintain-hondas-46563-3.html#post252145

Be thorough or you could end up wasting time and money.

. Perform K-Test on ECM:

The K-Test: Remove the MAP Sensor connector and turn the ignition switch to ON (Position II). Using a multimeter, check for 5 volts going between the MAP Sensor connector's reference wire (+) and ground. As you look at the connector, this is the socket on the right. Really press the black test lead into a cleaned main ECM ground on the thermostat housing. If the voltage is low, it's probably indicating ECM failure. Most failed ECMs will record a fraction of a volt. To me, the K-Test is simple, elegant, and accurate.

Two other, though less likely, reasons for the CEL staying on are a bad main relay or ignition switch.

What worked like a charm? What did the tests indicate was wrong?