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2003 Legacy L/SE Wagon (5 Speed)
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Discussion Starter · #1 ·
2003 5MT Legacy

I have noticed recently (I am not sure if I just haven't noticed it before) that sometimes when I go in reverse, usually when first starting the car up after not driving for a while, the reverse lights do not come on. Later on in the drive, I go to reverse and they work fine multiple times. I even can stop and get gas and reverse out and they work fine too.

I have checked and the reverse wire to the autodimming mirror follows the behavior of the reverse lights themselves, so I am confident it is not a bulb or hatch wiring that is causing the issue (unless the reverse signal going to the mirror first passes through the bulbs, but I doubt that is the case. Should I just order a new sensor or is there something else that could be causing this?

Electrical system is great, alternator is OEM and running strong and battery is only a few months old. Grounds are clean and so are the terminals.
 

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Checking the reverse wire for the autodimming rear view mirror was a good idea, however, the mirror reverse wire is powered by the same 12 V that is sent to the back-up bulbs when the tranny is in reverse. (Power from a fuse goes to one side of the back-up light switch on the transmission. When in reverse, the switch closes, and the power goes through to the back-up bulbs and to the mirror wire, so the mirror wire should have 12 V when reverse gear is selected.) Consequently, the fact that the mirror wire does have 12 V when in reverse does not confirm the back-up bulbs or the wiring to them.

I'd probably start with the bulbs. There might be bad contacts where they fit into their sockets, or the bulb filaments might be failing. Although the 2005-9 have a definite problem with wiring to the rear hatch (where it goes through the flexible boot between the car body and the hatch), this would be rare in the previous generation.
 

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2003 Legacy L/SE Wagon (5 Speed)
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Discussion Starter · #3 ·
Checking the reverse wire for the autodimming rear view mirror was a good idea, however, the mirror reverse wire is powered by the same 12 V that is sent to the back-up bulbs when the tranny is in reverse. (Power from a fuse goes to one side of the back-up light switch on the transmission. When in reverse, the switch closes, and the power goes through to the back-up bulbs and to the mirror wire, so the mirror wire should have 12 V when reverse gear is selected.) Consequently, the fact that the mirror wire does have 12 V when in reverse does not confirm the back-up bulbs or the wiring to them.

I'd probably start with the bulbs. There might be bad contacts where they fit into their sockets, or the bulb filaments might be failing. Although the 2005-9 have a definite problem with wiring to the rear hatch (where it goes through the flexible boot between the car body and the hatch), this would be rare in the previous generation.
Hmm so that is how it is wired in. The bulbs appear to be good, as they will work later on in the drive. I meant to say that both the mirror and the bulbs either work or do not work at any given time, which makes me think the problem is upstream of that fuse as neither are getting that 12V signal.

So simply, since neither the mirror nor the bulbs work sometimes, and all other times they both work, it is likely something upstream of the fuse?
 

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Ah, that's different. I thought the mirror reverse wire was getting the 12 V when the lights at the back were not turning on. But, if it is as you clarified, i.e., "both the mirror and the bulbs either work or do not work at any given time", then it is upstream.

So, again, power from the fuse goes to the switch; when the switch is closed (when in reverse), the power goes through the switch to the mirror wire and to the back-up bulbs.

The fuse is upstream of the switch, and the switch is upstream of the wire and bulbs.

There could be a bad contact where the fuse plugs into the fuse panel which might be intermittent. Simple test/solution is to remove the fuse and, preferably, replace it with a new one of the same amperage. It's a 15 Amp fuse in the cabin fuse box, identified in the Owners Manual (page 12-6&7) as #18, for the Backup light, Cruise control, & Backup light & ABS control. But note: if the fuse is the problem, it would affect operation of the cruise control, which should be checked.

That said, the back-up switch on the transmission is probably the issue. It's been seen before. There's two wires that connect to the switch. There have been cases of one or both wires weakening and breaking away, disabling the back-up lights. Or, there could be a bad contact in the connector. But given the intermittent nature, I wouldn't be surprised if the switch isn't going bad -- also not unknown.
 

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2003 Legacy L/SE Wagon (5 Speed)
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Discussion Starter · #5 ·
Ah, the previous owner did say that cruise control sometimes didn't work and I've noticed that rarely too, it very well might be the fuse in that case! I'll swap that out if I have an extra (I might have used it on the auto dimming one that randomly blew a month ago).

The switch isn't even terribly expensive from the looks of it either, either way it isn't looking too bad. Thanks for your help, I'll report back after swapping the fuse and taking a look under the air box at those wires
 
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