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Discussion Starter · #1 · (Edited)
A local tragic accident where a child was killed by a minivan backing up prompted me to install commercial-style back-up/reverse alarms on all of my cars.

You know, when a bulldozer is backing up and it makes that BEEP-BEEP-BEEP sound? Like that.

Our older Honda was easy to retrofit, using off-the-shelf alarm+bulb replacements (albeit not very loud), but our 2007 Odyssey uses exotic, tiny bulbs for which the alarm+bulb replacements are too big or fit poorly.

After about a month of on-and-off prodding and probing, I broke down and totally tore-apart the rear tailgate, and was surprised to find that there is a good-sized void to the immediate left and right of the license plate/car tag space on the tailgate that isn't immediately obvious. It's just large enough to fit the smallest commercial-style backup beeper.

To access this space,
1) take all of the interior trim off of the tailgate
2) take off the license plate, and then the plastic trim panel behind the license plate.
When fitting an alarm (or whatever you're smuggling) be sure to do a lot of fit tests with two-way tape before drilling anything. It's a very odd-shaped space.
To power the alarm, tap off of one of the reversing lamps; I fed new wires through an existing weather grommet for the license-plate-light wiring.

As for the interior trim, the pull-handle is the only portion of the trim screwed-down; the rest are pop-on body panel fasteners, and beware that the tailgate latch threads through the trim. (I broke a lot of the fasteners getting it off; though replacements are readily available at NAPA dealers, does anyone have a good guide as to the "right" way to take the tailgate interior trim off?)

As for the license plate trim and surround, it is held on both with bolts and body-panel fasteners, and a couple of the body-panel fasteners are hidden and hard to release (one is immediately behind the license plate, another is totally hidden and you'll have to just rip that one off). Another warning--two of the body-panel fasteners actually hold the gate-mounted tail-light assemblies on, not the exterior trim. And one final off-topic warning--the license plate exterior tailgate trim interferes with the gate-mounted tail-lights; put differently, if you need to replace a damaged gate-mounted tail-light assembly, you have to take all of the stuff off that I describe here. Grr.

The alarm I bought was the smallest commercial alarm they had at NAPA. Even the smallest one is loud enough, believe me.

Weatherproof all electrical connections; rainwater from the back window intentionallly slides through the hidden space.

The backup alarm was rated electrically at 350ma, though I measured it and it actually drew continuously half that. Nevertheless, to avoid overloading the reverse-light circuit, I replaced the halogen reverse light bulbs with brighter and lower-current LED equivalents.

The alarm conducts sound very efficiently to the sheet metal of the tailgate (turning it into a large speaker!); I added some insulation on the inside of the tailgate, behind the alarm, to reduce unwanted sound inside the car.

Now, when I put my Odyssey in reverse, it is impossible to miss hearing the alarm behind the vehicle (standing right behind it'll make your ears ring), and the LED lamps provide a lot more light at night for the reverse camera. I don't have any pictures of the final installation because it is totally hidden.

An alternative place for a backup beeper is inside of the rear bumper. I have not taken the rear bumper off so I can't give many details. The reverse lamp circuit is available on the breakout box in the passenger-side rear corner of the vehicle, and wiring could run the same way as the trailer hitch wiring. My Odyssey has a factory towing package, and there was so much wiring already there (and so many more trim panels to take off) that with better sound projection on the tailgate than behind the bumper, I opted to put it where I did.

Any questions, please post here; I am not sure when I'll get to them but I will try.
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