Small light fuse clears when switch turned one click to parking lights. I'm very familiar with electrical troubleshooting as I've worked as an instrument mechanic for 23 years, but having a hard time finding the fault.

The tail light relay coil side loop thru the headlight switch is good to go, no ground fault. I removed the tail light relay connector from the relay control module and the wiring to the lights is still showing a ground fault, so this eliminates the control module relay as the culprit. I then disconnected from each lamp one at a time, ground fault still present. I removed the driver's side molding under and around the steering wheel and checked all wiring with my Fluke set for a continuity tone to give me an audible alert if the fault went away. I also did this for harness under the hood, middle of car, and trunk. No luck finding the fault.

Schematic shows the taillight relay supplies power to 8 lamps, 2 front of car and 6 rear. I spent a good 4 hours looking for this fault and I'm at point now of either installing a slug and looking for a puff of smoke (kidding) or just running new wire.

Has anyone had this problem and actually located the ground fault. If I could figure out where the wiring splits into 3 parallel circuits, I could narrow down more, but with everything bundled and a cramped location it's going to be hard to find. I could get a tone generator, but would rather not have that expense.

Any help is appreciated, thanks.



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Is the taillight relay is integrated into the relay control module where you can't remove the relay and test pins?

 

Regardless of the relay, you can isolate the three legs coming out of the fuse box by unplugging connector H on the back of the under hood fuse box.

The diagram you attached looks like the 03-05 setup in my shop manual. The 06 is only slightly different. Does your accord have LED left and right taillights?

Pins H13, H14, and H1 (this is I1 on the 03-05 accords) should all be red/blk wires. H13 is the left front, H14 is the right front, and H1 (or I1) is the rear lights. Make sure the wire colors are correct before testing. The pin-out is shown for the H connector on the B0178 troubleshooting tree. Connector H location is shown in the fuse/relay box diagram earlier in the electrical section.

If you use your volt meter, you should be able to measure resistance from each pin to ground and you should see the lowest resistance bulb in a good circuit. A shorted circuit should show almost zero resistance. I'm not sure how your meter is measuring a ground fault or where you were testing with the bulbs unplugged, as each leg should be separate coming out of the fuse box.

 

I did remove the relay connector from the back of the relay box under the hood, still showed a dead ground on the wiring.

I'm using a fluke 87, connected to one of the Red/black wires with other lead to chassis ground and reading continuity. Showing 0.8 ohms to ground. I've pretty much ruled out all the end devices, only thing left would be the wiring. This is my daughter's car and she gave me the Haynes manual with the schematics. The wiring I'm seeing does match what's in the schematic.

 

My Haynes manual shows thru 2007 Accord. I'm not a car mechanic by any stretch of the imagination, are these manuals known to have bad info?

 

Forgot to mention, no led lights and taillight relay is integrated into the box. Would have to replace the whole box if the relay was the culprit, but I don't think it's the problem based on continuity reading.

 

Are all three legs common in the connector H or at the relay? If common at the relay, then ground is definitely inside the car since I disconnected the H connector and still showed the ground at the license plate wiring. I'll remove the connector again and check the 2 front lights. This really helped me as my schematic doesn't show pin assignments. Thanks!

 

Any idea where the circled connector would be in the car? If I could disconnect here, I could eliminate half the inside wiring.

 

I am not familiar with 2006. But, can you follow the tail light wires from back tail lights towards the side rear fenders?
It would seem the "split" to the rear lights would be near the gas cap inside the trunk, or on the other side near the rear wheel.
You will have to remove the trunk carpet to expose everything.

 

I found the splitter connector in the back seat on the drivers side, was in the same area as the rear air bag. Unplugged the connector and checked back to the lights, no ground, so problem is from this connector to the relay connector under the hood.

I opened the plastic conduit under the driver dash and found the red/black wire in the bundle. Cut wire and checked wire going back to the trunk, no ground. Checked wire going to the relay connector, dead ground.

Looks like this ground is in the area I hoped it wouldn't be, being so inaccessible. At least I have it narrowed down to about 6 feet of wire. May just have to push a new piece of wire from the relay to where I cut the wire at the dash. Never tried to run wiring thru a firewall, it that possible using the existing penetration? Figure I could push something stiff and non conductive thru the penetration from inside the car, attach a piece of wire and pull it back thru. Does this sound correct?