# Centre rear brake light fuse location?



## plano-doug (Jul 1, 2015)

ralph1981 said:


> Any tips on other things to check would be appreciated. I am trying to work out what is at fault, so I do not buy a new brake light needlessly. Tomorrow I will test the brake light connected to the car battery.


You don't mention the year, but looking at a 2012 schematic, the BCM controls the tail lights. From the BCM, connector X4-pin 11 goes to the center brake light. There are 3 fuses shown providing power to the BCM, and all 3 are in the instrument panel fuse block. I would check F24DA first, then F23DA, then F3DA. (That's how they are labeled in the drawing; not sure if they're labeled the same way in the fuse box.)

If it's not a fuse, the next step, if you can, is to probe the BCM pin with a meter to be sure you have the signal at the source. Then go to the other end and inspect to be sure the wires are properly connected at the light. After that, it starts getting tricky because you have to start disassembling things to trace the wiring.

I believe the BCM is located on the hump above the passenger's left foot. (I haven't worked my Cruze's BCM yet, but if it's like the ones on my Impalas, it's not too hard to access.)

Also, before tearing things apart, try checking the ground. The 3rd brake lights shares ground number G309 with the left rear brake light. So you can trace the black wire from that light - there will be a junction with another black wire from the 3rd brake light. Make sure the junction is in good condition.

HTH.

Doug

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## ralph1981 (Jul 29, 2019)

Thank you for the reply plano-doug.

The car in question is a Holden flavour of the Cruze JH 2012 sedan 1.8L. I should have mentioned that.

I checked the BCM fuses 31 & 32 in the engine compartment then 3, 8, 9, 10, 23 & 24 also all BCM fuses in the left side of the glove compartment box (there is no fusebox on the drivers side on my model) and all were ok also. The 2 amp BCM fuse housing in the glovebox did seem burnt, maybe it was stressed when the surge or what not happened. Logically this could be the fuse for the middle brake light as its current draw should be well below 1 amp to the leds.

Before checking the fuses, I did try testing the voltage on the middle brake lamp connector but found nothing. I may have had a poor connection as afterwards I tried again and shoved the multimeter probes into the plug and got 12.3v. I did not do this initially as I was worried I would damage the pin sockets on the plug.

The middle brake light PCB is dead. I applied 12v to it and nothing lit up, I then applied directly to 3 leds connected in parallel, they burnt out ? then tried 5v on other leds and they lit up. This PCB uses rectifiers, resistors and a varistor to limit the voltage to the leds.

Wreckers quoted AUS$65 (US$40), however I am going to try repairing it myself with 12x 2 volt 5mm red 1500 mcd leds with 15 degree viewing angle, and a 15v voltage regulator (reduces 14.5v to 12v) with the 6 leds connected in series. This will cost me about AUS$30 to repair at most. If you order online, you can get such leds for a couple of dollars. I have to get this fixed quick so buying from the only electronics store in my city at AUS$1.35 each.

I will post a DIY if I succeed in the middle brake light repair.

Cheers,
Rauli


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## plano-doug (Jul 1, 2015)

ralph1981 said:


> Wreckers quoted AUS$65 (US$40), however I am going to try repairing it myself with 12x 2 volt 5mm red 1500 mcd leds with 15 degree viewing angle, and a 15v voltage regulator (reduces 14.5v to 12v) with the 6 leds connected in series. This will cost me about AUS$30 to repair at most. If you order online, you can get such leds for a couple of dollars. I have to get this fixed quick so buying from the only electronics store in my city at AUS$1.35 each.


Hi, Rauli, 

I admire your initiative. I only have a little experience with LEDs. I think they're supposed to be driven with a current source, but those are not easy to design - they're for analog guys, and I'm digital  

Anyway, I've used a voltage regulator to drive a constant voltage to LEDs, so what you're trying makes sense to me. The only concern I have is that you're not allowing enough drop out voltage between the car's B+ and V-LED. For example, if you use an ordinary linear voltage regulator with 1.5V of minimum drop out, and your 2V LEDs are grouped with 6 in series, V-LED is 12V. Add the regulator drop out, and you're at 13.5V. So any time B+ drops below 13.5V, the LEDs may start to dim. 

OTOH, if you group the LEDs with 3 in series and set the regulator for 6V, then you'll have about 7.5V of drop out across the regulator, which leaves lots more head room for B+ to sag without causing the lights to dim. And, since the LEDs draw little current, there's probably not too much concern about power dissipation in the regulator.

That's just some thinking out loud. Maybe grouping them in 4's or 5's would suffice. Maybe grouping in 6's isn't really a big deal, either. But it's one of those things you think about in circuit design. (Keep in mind, 15% of the design implements the desired functionality, and the other 85% takes care of all the what-ifs  ) 

As for protection, I'm really rusty, but an ~18V zener on the regulator input should provide some protection against spikes on B+. That in parallel with a varistor and capacitor are pretty common from what I've seen.

BTW, the 3 fuses I mentioned are 20, 20 and 25 amps, respectively. So the 2A fuse you found is yet another one feeding the BCM, but wasn't shown on my brake light schematic. So it may not pertain to them.

HTH.

Doug

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## boony00 (Aug 5, 2021)

ralph1981 said:


> Thank you for the reply plano-doug.
> 
> The car in question is a Holden flavour of the Cruze JH 2012 sedan 1.8L. I should have mentioned that.
> 
> ...


Hey Rauli - How did you go with this fix? I've got the same problem and have heard its a diode issue that can be repaired but can find little information on this.
Thanks
Andre


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