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Reverse light out, but works in dim mode

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Got a bulb on passenget side in my reverse light that is not working in reverse.


Are these 2 bulbs in one?


When parked or in neutral. Its on, but dim. The same with driver side. It's dim when in park or neutral. But it works ok in reverse. brightness up.


Is this a bad bulb? Never seen a 2 stage bulb. But doubt its a fuse since I'm assuming each headlight are on same fuse

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  • 2 weeks later...

Many of the bulbs on your car are "2 stage". They're actually dual filament... a single bulb with two filaments inside - one that's bright and one that's dim. They are commonly used for turn signal and parking/running lights. The bright filament flashes for the turn signals while the dim filament provides parking and running light functions. Same thing with the brake/tail lights - the bright filament is used for brake lights while the dim filament provides tail lights (they're not separate bulbs).


On the other hand, the backup lights don't use dual filament bulbs. What you're seeing sounds very much like a bad connection on one of the bulbs. Often this is on the ground side of the circuit. What happens when there isn't a good ground is that the electrical current will "back feed" to ground through the other bulb on the same circuit causing both to light more dimly than normal (because there is twice as much resistance as normal from going through the second bulb). When the circuit is put in use (you put it in reverse), both bulbs are getting power so there can't be any back feed anymore and only the bulb with the working ground will illuminate - the other will turn off.


While the symptoms you describe most commonly indicate a ground problem, there are other wiring situations that will cause the same symptoms. In this case, I would be concerned that the backup lights are on at all (even dimly) when the car is not in reverse. There should be no power at all to those bulbs when the transmission is not in reverse. So I suspect you may have a short between another circuit and the backup lights that is powering the circuit when it shouldn't be. That would be extremely unlikely unless some modification has been done to the wiring - the most common culprit being a trailer connection.

Edited by TheWizard
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