Remove the bulbs from the back-up lamps. Now you can check continuity to ground on the (+) wires for those lamps. With the bulbs removed, there should NOT be any continuity to ground from the hot wires.

I guess that would be the wire on terminals P5 on the 2nd picture that RedBull posted. If the P5 wire is worn through & touching bare metal, that would blow fuses.

I am trying to figure this out. I am using a 6-24 volt testor with a small bulb in it.
When I attach the alligator clip to the lower side of the fuse #21 connector and the pointy lead to the upper side the light is always on, although dimly, meaning I have a partial short - I think, right?
When I put car in Reverse, the bulb glows brighter, meaning that's what would cause the fuse to blow right there. But should I not be seeing a constant dim light? I tried another (working) fuse and it did not light at all.

Jim - I will try the continuity to ground test with bulbs removed. Although I have disconnected the Green wire that power the reverse lamps at the rear seat driver side shoulder area behind the seat and trim there, and still have the same fuse blowing in reverse.

Good. Since you've disconnected that and the fuse still blows, that means the short is "upstream" of where you disconnected it. I guess you unplugged it at C752 in RedBull's diagram?

Can you disconnect the wire up at the P5 terminal at the MICU? It's beginning to act like some part of that wire (from P5 to C752) is rubbed through & touching metal.

It does sound like he unplugged C752, located behind the left C pillar.

I am still wondering what all is plugged in or not, when he said the only way he can put it in reverse without blowing Fuse 21 is by disconnecting the C201 connector.

Ah yes, it's certainly C752 at c pillar I disconnected and fuse still blows in reverse.
And it's only unplugging C201 that makes the fuse stop blowing in reverse (with everything else back plugged in).
But is that simply cutting off the "return" current of 12V from the Trans Range Sw completing the reverse circuit and therefore interrupting sending it further upstream?
in other words would I check wiring between C201 and C152 or
Check P5 wire from MICU to C752? Thanks!
To say I'm a newb to electrical theory isn't totally off base here.

From C752 at the C-pillar, check the wire that goes forwards to P5. Check whether that wire has any continuity to ground.

What I'm thinking is that you might have a short-to-ground in the wire between P5 & C752. It doesn't blow the fuse until the controller switches the backup-lights ON.

Then similarly, check whether the wire from C201 to C152 has continuity to ground. But I suspect a short in that wire would blow the fuse 24/7 - not just when you shift into reverse.

Ah interesting Jim, thanks.
That does sound good theoretically to me since you've explained it that way. And it also seems there would be chance to short P5 to C752 anyway with the car frame right there and possible wear points in the plastics over the cable harness in the side floor panels.
I will check that pronto again. I've now wound up yet on the opposite side of the country from the car again on a family vacation.

And yes perhaps the engine bay wiring side, being shorted there, would short the fuse always with car in any key position all the time. And the voltage sounds like it must travel up from the trans switch back to MICU and down the line to short out when in reverse.

(Ok, flew back to area and Ohm-ed car now.)
With C752 C pillar connector disconnected and a 19 pin connector at the MICU - the vertical green connector just behind the inside kickpanel main fusebox - I Ohmed and grounded to a good body ground and DID GET CONTINUITY to GROUND on the green wire - tested both ends of green wire to be sure and tested about 9 other wires while in there.
The odd thing is I am also got a continuity to ground on a purple and black wire there - hmmm... maybe that's in fact the ground wire?... now I feel a little silly about that, I was suspicious... Don't have complete wire pin diagram for MICU.

But it looks like the tentative diagnosis is:
I have a short to ground from MICU Pin 5 (green with grey dots wire) somewhere running up to the rear C pillar driver side C752 connector. I will post my final results and fix as I find it.
Thanks to Jim, RedBull and Poorman for all the help so far!!!!!

Nope. That's not it. I have a short on this circuit, but it's not anyway up to the C Pillar C752. There's multiple connectors up over the fusebox that are not listed on any wiring diagram. There's some secret 3 way split on the green wire between about a 12" stretch of two large white connectors, and it's shorting to ground up there somewhere I cannot see.
there is a black plastic small wire going out of area to top left of the dashboard area - perhaps towards engine bay / firewall, and that must be the grounding to short cause in there or beyond.
If I disconnect all these I only short to ground up there, not at the back of C752 anymore.
so annoying this issue that goes on and on.

Can you post a few pictures of the driver's under-dash fuse box area;so, I can get some bearing of what you're describing and possibly try to find more info.?

Also, take a picture of the wiring connectors near the fuse box, to the left of the Data Link Connector (aka OBD II port).

isolated short to ground - sort of
 

I tracked it back after disconnecting all kinds of things, to isolate, and the only source for making the short to ground is a small black plastic wrapped wire(s) going up from above fusebox area to the A Pillar driver side.
The SRS airbags are there, so I am afraid to pull out all the stuff there.
What on earth goes up there?
Car has moonroof. could it be something that connects on that circuit only when reverse completes the green wire circuit??

1st pic has pencil pointing to 'bad' wire. this is only possible cause of getting shorting to ground readings. This continues on up the 'A' pillar driver side.

2nd pic is farther back showing left of steering wheel area, where the moon roof switch panel has been removed to trace wiring behind it.

In your second picture, I see a ground wire added for some aftermarket electronic accessory? What is that connected to? Many times aftermarket electronics are the cause of problems.

In your first picture (post #51), next to that black wire, the LT Grn 28 cavity connector is junction connector C405 and the LT Blu 28 cavity connector is junction connector C406. If your car was a manual transmission, then part of the circuit for the back-up light switch from C752 runs through C406; however, your car is an automatic; so, it doesn’t run through there.

For your automatic, there's actually a couple more junction and splice connectors in the circuit for the back-up light switch. For the automatic, junction connectors C501 and C601 (For your EX) are also in the circuit.

I haven't found what that black wire/cable is yet; but, I'm not sure if that would cause the problem for the No. 21 fuse blowing.

It does seem a little unlikely that it's causing all this, however, with that wire connected to whatever it's connected to, it is measuring a short to ground on the green wire, and if all connections are connected, that causes the P5 green wire from the MICU to the C Pillar C752 to also register a short to ground reading.
I ALSO discovered a very odd 2 Amp fuse right up in there, it looks like a 3 wire termination point, but in fact it's black / yellow 3 way tie in which I assume is either hot 12 VDC or switched 12 VDC. I don't know if it's related at all, but that fuse is toasted shattered inside.

I've pulled apart nearly everything in that region, C501, C502, C601 etc etc... (C405 and C406 aren't involved in the short to ground matter so they were left as is).
the only thing that has no connector to disconnect that's still in line with the short is that wire going up the A Pillar. I have a very short multi wire 12" connector with two white ends disconnected at Both ends (so it's like a floating wire), and both green wires register short to ground, (and also still the green wire on fog lights switch connector on the dash ALL reading short to ground). At that point on the two white connector cable that's completely disconnected, the only thing left I haven't disconnected to this floating unhooked wire is a spliced in T joint black wire casing - that's the one in my picture that goes up the A pillar. That's all that's left down below to give the short to ground reading.

I think that's not a wire going to ground. I'll go check. But this car is completely stock. Only factory (or dealer) supplied options. The car was bought new by the family and never altered.

If you can, try to take some more pictures of where that black/wire cable may comes from or goes to; so, I can try to find what is may be related to. Just seeing part of the wire makes it hard to search for the circuit.

Also, try to take some pictures of that 2 amp fuse, related wiring, and 3-way termination point.

So far, the only wire harness I see that goes up the driver's side A-pillar is for the driver's vanity mirror light, ceiling lights, ambient light, and moonroof. However, the only thing I see on that roof harness that might have anything to do with the back-up light circuit would be at the C601 junction connector, which you said you unplugged.

Junction connector C601 is related to the moonroof circuit for the EX and EX-L trim levels.

Ah wise you are RedBull. I thought it was all stock. I was wrong, and you're right, it IS some aftermarket thingee.
There is a multipin computer style black connector on one side. it looks like a computer charger or weird XL iphone kind of charger.
Also there seems to be a black sensor that was glued behind the dash on the right of the steering wheel area and directly in front of that was a piece of velcro adhered on (which goes to nothing we have).
I am not quite sure what it does, but it connects into some very large gauge wires that are crimped and barrel crimped off things in the fusebox area. If I disconnect this setup the car won't start.
No idea what it is, but calls will be made to track it down. I asked main owner of the car for past 6 years and was told that sometime they 'think something went wrong with the power door lock / key fob' - they 'think' but don't really remember.

The first pic is the 'sensor' glued behind dash. You can tell by slipshod way it was wrapped around things, this was NOT Honda work.
Other pics are the other side plug in that goes to nothing. and also the power source with heavy amp fuse I think.
I guess I thought at first this was the diagnostic plugin, but I found that farther up.

And, um, feeling a bit sheepish, I'd better go and double check I pulled that C601 connector.

This is a very long thread, and I just tried to re-read it. I have a simple question. What number fuse is blowing according to this picture you attached earlier?

https://www.hondaaccordforum.com/for...e-21-image-jpg

The fuse #21 "IG Meter" is blowing anytime I shift into or past 'Reverse' on AT. All components in that circuit I've tested are fine.
Have short to ground on it, on the green wire.

RedBull: Just pulled C601 which in my 2004 EX AT is a 7 pin connector, yes 7 wire. And that made no difference. The Green wire is still reading continuity to ground with that disconnected.

I just discovered with all the fuses back in (and not in reverse) the mirror on the car is dead. There are two black buttons on it, a sensor and three wires in and out of roof. Moonroof has full functionality as does interior map lights both manually and on door setting.
Could this be the cause? That mirror must be powered up the A pillar enclosed wire case, the one that seems to be making my meter read continuity to ground on the green (reverse) wire.

I also see on wiring diagram that there are two other things spliced into reverse circuit: "navigation unit" and C601 + C602 "option connector". I don't know what these do. Is there a in mirror compass that determines position for nav unit??
I have the EX model. Not sure what options were on it. I've never used a nav screen on the 6 disc changer.

I'm a little confused by your last post. Which mirror is dead? Is it the driver's vanity mirror light, the side powered mirror, or an add-on Honda automatic day/night mirror with compass?

If you have the automatic day/night mirror with compass, that black wire harness may be for it. Usually on the newer generation Accords, only EX-L (leather) trim came with it; it was an add-on for most other trim levels.

http://www.handa-accessories.com/accord/04-mirror.pdf

If you have an electronic type mirror, can you take a picture and post it; so, we can see whether it is an OEM accessory or aftermarket.?

Sorry should have been more specific.
Right, it's the driver interior rear view main center windshield mounted mirror.
Factory leather installed EX model.
Yeah, was thinking this wire runs up to that mirror thru the A Pillar.
What the heck is that green wire "option connector" that's Ts off the green wire that runs to the MICU and onward to the rear brake lights?

The C602 "option connector" is used for your automatic dimming mirror. It is not used if it was other trim levels without the auto dimming mirror.

You may have found the source of your problem.

The pic 4 & 5 above
and on this post pics show more detail of wiring which I am almost sure is not factory to that oddball accessory that is not connected and I have no idea what it does, it also connects to that weird glued behind the dash sensor, and as mentioned earlier car will not start without it hooked in.
There is also a pic of probably non factory hot splice into a black and yellow power lead - that plastic butt end connector simply housed a (blown) 2 amp fuse. Last pic is weird computer looking connector to nothing.

These butt connectors and wire connections do not look stock. Are they part of that other aftermarket accessory (not the auto dimming mirror) from the earlier posts we talked about?

Edit: You posted right before I posted this one.

Woohoo!! this gives me something to look forward to when I get the car back from my gf tonight. (At least I can hope for a few hours before facing the music and partying or back to drawing board).

THANKS REDBULL!!!

Yeah, that's that weirdo aftermarket looking accessory. It's all tied in together. Seriously, if you saw the stupid way someone wrapped a black two wire cable around raw metal framing under the steering wheel and compared it to ANY Honda wiring I've ever seen in this car or my Integra you'd know right away that's not factory.

I don't think this is, in fact, tied into the back up light / green wire circuit in any way, but it would interesting to know just what the heck this is. And again, I can't disconnect that butt spliced hack job from power or the car won't start. There is an alarm, but I always thought it was factory installed. Has pro looking red blinky on dash and 'panic' on Fob which still works if I unplug that weird set up.

That thing has a huge inline fuse - rated 40Amp I think (??), and only powers the hidden glued in sensor to right of steering wheel, and that computer plug in thingee. The gauge of the wire that's super thick and that large inline fuse makes me wonder what the hell is needing to potentially pull all that power? Is this the end? Had Big Brother gotten to all our cars and recording everything we do? :)

I also agree that the aftermarket accessory (whatever it is) would probably not be tied into the back-up light circuit. It does not seem logical for any purpose, if they did.

Oh holy SH*T!!
REDBULL - thanks for that last wiring diagram I've never ever seen anywhere!!
So - that is where that 2 amp fuse is, and where that black / yellow wire was tapped as a split and was blown. I kept wondering why it was blown, now I think I know.
Must be grounding to frame in either the A Pillar or roof area that darn green wire.

(now as to theory, why oh why, is a auto dimming rearview mirror tied into a back up light circuit?? And could wiring diagram authors have been a little more explicit instead of writing 'option connector'? How could I know that's there casually looking? I'd have to have access to that last diagram you provided.)

My memory is a little fuzzy right now; but, if i remember correctly, when you put the car in reverse, the auto-dimming feature may be turned off or something like that. There was a discussion on another forum before, where people were trying to tie into those wires to power other aftermarket electronics and it was mentioned that in reverse, it won't receive power on a certain wire.

I was thinking, maybe it is circuited that way to override the nighttime or bright light in rearview sensor and provide Maximum rearward brightness vision in the mirror itself when in fact, backing up.

Also, I have a bad feeling I'm going to have to wrap this up with a "there, I fixed it" confession. I will confirm tonight if what I did on Friday June 7th did all of this.

Problem solved. Thanks to all the help on this forum!!
And especially thanks to RedBull for the final help and missing electrical wiring diagram.

So the, uh, problem was something, uh, I did.
"There, I fixed it" was basically what I said in June when I found a new bolt to replace a missing head visor bolt. I was being careful but somehow I managed to pinch the black - yellow and green wire four pack to the auto dimming mirror.
The wires were jammed and crimped by the metal attachment point of the visor and just barely cut a wire strand width from the green wire sheathing. The green wire was shorting right there and took out my whole back up light circuit.
I'll post a pic tonight of what it did. It was somewhat minor but big enough to give me headaches and fits for 2 months.

Glad to hear it finally was fixed, this thread was getting very long without resolution. Yes, please post the picture.

Here's the pics. The four wires got wedged between visor mount. 4 wires crimped a bit 2 with very slight tear thru the insulation. I pulled wires out of headliner cut and pulled back the black sheathing and then electrical taped the wires to insulate them as they are. Now I can go into reverse!

Dang.......you found it. Nice job :)

Thanks Pooman! This was quite the nutty repair for me. I really wished I remembered I tightened up that sun visor that day... could have saved me 10 + days of work.

(I remember seeing the wires there, and trying to make sure they would not get hit by the bolt, they didn't, but got pinched by visor mount instead. I watched the area for any sparks / smoke in case I struck a hidden wire and then completely forgot all about it when nothing happened).

Many Many Many Thanks!!!
 

I just want to thank you all for the many hours of work diagnosing this issue. I had a similar problem with my '05 EX-V6 and it was making me crazy. I spent hours diagnosing the obvious added iphone connection, back up lights, etc, etc. Then, by the grace of God, I found this thread. I read the first few pages early on in my experiment, but yesterday I finally read through to the end. Well, don't you know I had my headliner replaced after moving to Florida last year (Florida killed my AC and my headliner instantly, thank you very much). I am the original owner, so I know everything that has been done to the car. Of course, I completely forgot about the headliner until I read this. In any case, I pulled the harness out for the auto-dimming rear view mirror and, voila!, bare wire is exposed!!

Where may I ship the case of beer?

Haha!!!!

Thanks man.

You know what, I have a huge grin here. I am thrilled if it helped someone else.
I mean, I was almost pulling my own hair out on this one.

Excellent news you stumbled on this thread and it helped you! Congrats on the diagnosis and fix!