They said it could be my wire harness but what do I look for

The ECM likely failed.

Turning the ignition switch to ON (Position II), not START, does the CEL come on and then go off after 2 seconds? If not, the problem is with the ACG (ALT) (S) 15 amp fuse, in the under dash fuse/relay box; ECM (perform the K-Test, below); main relay; or the ignition switch. Perform tests in that order.

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. Many Hondas parked for several years are now back on the road. "The K-Test creates massive value, by providing a low cost solution where one did not previously exist."--TxGM