Hi All

I was checking all the lights on my 2007 GP before NCT test tomorrow. I find out that my reverse light is not working. I changed the bulb and still nothing. The connector looks good and when checked with a multimeter it shows 12V on the bulb connector. So I checked other bulb and still nothing. And here is the strange thing... when I connected LED bulb it is working but it doesn't give any light it is just glowing, looks like it doesn't get enough power to light properly.
I checked it both with the engine running and off.

Any ideas why it works this way?

A bit of theory ?

Here we go:
thanks to its high input impedance, a multimeter draw a very(very) little current from the circuit it measures the voltage.
When current flows through a resistor, there is a proportionnal voltage drop: the higher the current OR the higher the resistance, the higher the voltage drop (ΔU=R*I).

In your case, since I (current) is very small, there is almost no voltage drop so your 12V reading is normal, even if there was a resistance in the feeding line (in electronics that's what called a pull-up resistor).
Now if you install the bulb, its relatively low resistance will allow a high current to flow thru it, current that will drop the voltage in the (issue) resistor resulting in not enough power (voltage * current) @ the bulb to glow its filament (will get warm-ish).
Same occurs with a LED bulb, but since they need less power they'd kinda glow but not at full brigthness…

To make the story short: You probably have a contact resistance somewhere (morelikely @ I020 GB switch), the mulimeter set to ohm-meter will help you here.

BRs, Bernie

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Thanks, Bernie

I checked the reverse light circuit and you are right it looks that switch on the gearbox is faulty. I ordered a new one I will replace it over the weekend.

Any advise or better a guide how to replace the reverse light switch on a Duologic gearbox?

The gearbox itself is the same, being dualogic or manual, so you just have to disconnect the sensor, unscrew it and install the new one …

BRs, Bernie

If someone here helped You fix -or better, understand- your issue, hit the thanks icon @ bottom right corner, it's free and makes us feel helpy ;-)