I have a 2003 Accord Coupe 6MT. Love the car.

While on a recent trip, I lost driver's side low beam. Replaced the bulb, but still nothing. Fuses for both low beams test good. Tested voltage at the fuses: 14.2V on working passenger headlight (engine running), but no power at fuse for dead light. High beams work fine and all other signals, etc, work fine. In case it matters, I did get some mV fluctuations from the fuse connectors when I had someone turn the switch on and off, but only up to about 50 mV.

Among my theories:

Bad relay? (where the heck is it located?)
Bad ground?
Bad multi-switch stalk?

I'm going nuts looking for the headlight relays. I've pulled every relay from the underhood fuse box with no impact to the one working headlight. None of the cabin relays appear to be marked for headlights, either.



I found two clusters of groundwires bolted to the frame inside the driver fenderwell (pic). One was crusted in grunge, so I thought I'd found the problem. After cleaning, still no headlight.



When I have someone operate the headlight switch, I hear clicking from the underhood fusebox, but I don't think it's coming from any of the visible relays. Are there any components under the "box" to the right of the fuses in the photo? If so, how do you get to them?

 

The low beam relay, high beam relay, and a control block are inside that Relay Control Module ("Box") in the under-hood fuse/relay box. The Relay Control Module is supposedly built into the fuse/relay box.

Is it the number 1 fuse (10A) in the under-hood fuse box not getting power or is it some other fuse?

The ground (G301) is located behind the bumper (left side).

 

there is only one relay for both low beams, same for highbeams, so unlikely the relay is the cause if you have one lamp working. have you checked the headlamp connector for power?

 

Looks like you got the right ground connection.

 

First, thanks for the quick and knowledgeable responses.

No, I haven't probed the bulb socket because it's incredibly hard to reach. I figured it was unnecessary because there's no power at the fuse for that lamp, which I expect would also mean none at the socket.

 

Yes, redbull, the number 1 has no power. It is marked as lo beam for drivers side. The passenger side low beam is number 6 and has 14V with fuse removed and engine is running. Swapped fuses, same outcome.

 

Actually I didn't mess with the one you marked since it looked solid. The one I cleaned is the black mess just to the right. Is there a way to "jump" a ground somewhere in the circuit to test?

 

Although it may be something else, I am not so sure whether you can rule out the relay control module, as the only component/circuit protected by the No. 1 fuse is the left low beam headlight, and power runs through the relay control module to the No. 1 fuse.

This is a description of how the circuit works:

The headlight circuit is controlled by the Multiplex Integrated Control Unit (MICU) system. The high beam and low beam headlight relays are located within the relay control module.

Power Supply
With the ignition switch in the ON (II) or START (III) position, battery voltage is applied through fuse 21 to the MICU and to the combination switch control unit. Fuse 7 is hot at all times and supplies battery voltage to the MICU and to the combination switch control unit.

System Description
High and Low Beams
The high and low beam headlight relays are located within the relay control module (in under-hood fuse/relay box). The relays receive battery voltage at all times. The grounding and operation of the relays are controlled by the multiplex system. The combination switch control unit in the steering column receives information signals about operating conditions from the headlight switch and from the dimmer switch. When headlight switch is turned on and the dimmer switch is set to the high or low beam position, the information from both switches is processed by the combination switch control unit and transmitted from control unit-to-control unit across the multiplex communication lines. The relay control module will then ground the appropriate high or low beam relay to operate the necessary headlights. Because of the multiplex operation of the headlights, the headlights will always reset the low beams when the ignition key is cycled.

 

Eeek. So there's a possibility that the only relay not accessible may be faulty? Is there anyway to test it other than installing a new fuse/relay box?

Looks like a new one is $325 and a used one is about $75.

In case I do need to replace it, is the fuse/relay box plug/play? Does the wiring simply plug into the underside?

 

It is sounding like it may be the relay control module/fuse box. The battery should be disconnected and then waiting at least 3 minutes before attempting any work.

There are two bolts holding the alternator and battery cables, two fuse box mounting bolts, and 11 connector plugs under the box.

Found a similar issue like yours:
Honda Accord: Driver Headlight (Low) does not work - JustAnswer