OBC, no illumination - have changed lightbar

Mon Jun 23, 2008 3:55 pm

I'm going to get this working

I bought an LED lightbar off US ebay and I've swapped it into the OBC. Still no illumination even with the side/headlights on. What else should I be looking at?
It turns out that this is not the first time that the lightbar has been fixed, someone had soldered another bulb onto the original one but it wasn't identical. One was in a plastic socket the other one (probably NOT the original judging by the soldering) was slightly larger and didn't have the plastic surround at its base. Is it likely that the wrong bulb has caused problems elsewhere? Neither bulb from the original unit look to be blown.. how should I test this? (I don't want to risk putting large currents through either).
Cheers
Morat

Mon Jun 23, 2008 4:45 pm

You could test for continuity and hence intact filaments on the old light bar, if you have a multitester with a continuity function.
I thought the bulbs had blown on mine recently, but it turned out to be one of the fuses.

Mon Jun 23, 2008 5:37 pm

/me checks instructions on new multimeter..
Hey, yes I do!

So I can get a reading across both bulbs, and across both LEDs (infact the LEDs light up weakly if I use the 200 range) but I can't seem to get a reading if I stick the probes into the two sockets in the blue thingy at the end of the bar that plugs into the OBC. Maybe my probes are too fat.. or perhaps both blue sockets have failed in some way...Surely thats unlikely?

Which fuses are you referring to? are they in the fuse box under the bonnet or inside the OBC itself?
Thanks for your help

Mon Jun 23, 2008 6:56 pm

I'm fairly certain it was fuse 21, in the main fuse box. If both bulbs ore okay, I would definately go for the fuse.

I say that because when it happened to me I was all ready to pull the dash apart to get to the OBC, and for once in my life I thought No...I'll check the obvious first and I was lucky! It's not usually that straightfoward though.

Mon Jun 23, 2008 7:13 pm

heh, not in this case either, sadly.
21 was fine. I looked at some other likely 10A fuses but no joy. I'm starting to think it will be something inside the unit... which isn't great. It actually works fine - its just the illumination that doesn't!
THanks mate

edit: from other threads it looks like fuse 21 should be a 7.5A. This isn't looking great

Mon Jun 23, 2008 8:17 pm

I pulled out the OBC and found one bulb on the back - checks fine for continuity.
Also there is a single yellow wire that ends in a white plastic connector. I can't find anywhere that it might plug into. You can see it on the image below just touching the green plug that goes into the OBC. (just below the OBC unit itself on that photo)
I think the fitting guide in the OBC article mentions it (yellow plug) but I can't see where it is meant to go....

Mon Jun 23, 2008 8:31 pm

I've been looking at the circuit diagram to see if I could shed any light on the illumination problem (sorry!), still stumped on that. The yellow wire is not used on the E30 according to that.

Mon Jun 23, 2008 8:35 pm

Just to add that the single bulb for the buttons only illuminates with the side lights. You proberbly know, but just in case. Oh, and you're missing The Gadget Show if you're still fiddling with the E30.

Mon Jun 23, 2008 8:53 pm

Ah, its for the buttons - that makes sense.
I'm starting to think that the fault must be inside the OBC, which probably means I'll have to look for another one if inspiration doesn't strike soon.
Thanks alot!
Gadget show well and truly missed this week

Tue Jun 24, 2008 12:30 am

think ill check my fuse 2morro before i pull dash apart!!!!!

Tue Jun 24, 2008 8:54 am

If neither the light bar illuminates with the ignition on, nor the backlight for the buttons lights up with the sidelights on, then you have two faults. If they have a common cause, it has to be something to do with the brown earth wire between the OBC and the cluster.
Yellow wire is unused.

Tue Jun 24, 2008 9:34 am

Thanks Brian, but the buttons light up just fine - I just didn't realise what the bulb on the back was until I pulled it out. I was hoping it was a fuse.
So its just the lightbar, and I have two that should work. Which is worrying.
The OBC functions are all working, its just that I can't see them unless the light is perfect.