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LED bulbs 700

posted by oldyellr on Fri May 8 15:23 CST 2009
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last visit: Fri Oct 24 14:28 CST 2014

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Has anyone used LED bulbs in their Volvo? If so, how does that affect the bulb failure circuitry? I think that LEDs use less current, so using a pair of LED equivalents to replace a pair of 1157s could halve the current consumed the same as one burnt out 1157, would it not? Conversely, if you used a pair of LED 1157s in the taillights and a pair in the trailer lights, would the bulb failure circuit know there were 2 extra bulbs if a cheap non-powered trailer harness adapter were used?

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LED bulbs 700

posted by B.B. on Fri May 8 15:58 CST 2009
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last visit: Mon Oct 6 13:15 CST 2014

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The bulb out sensor is just looking for an inbalance in the current flow.
If both lamps in a leg are drawing the same current then all is OK.

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LED bulbs 700

posted by oldyellr on Sat May 9 01:52 CST 2009
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last visit: Fri Oct 24 14:28 CST 2014

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But if the same bulb is burnt out on both sides, the "current" would be balanced, but the sensor will show a warning. My sense is that it's looking for a total current within a certain range, say < +/- 50% of the expected current. Incidentally, I had no warning when one of my license plate bulbs was burnt out, probably because they're only 4W on the wagon, but when I try running my trailer lights off that circuit, I get the warning.

So, my original question was, will substituting equivalent LED lamps in the taillights set off the bulb failure warning due to the lower current? Those LEDs are more visible and have a much sharper on/off characteristic when flashing.

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LED bulbs 700

posted by TONY H on Sat May 9 10:28 CST 2009
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last visit: Fri Oct 17 16:39 CST 2014

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I added lighting to each side. And the Bulb out sensor was still happy.

You should be fine with LEDs. Except a trial I did on my 200 shows that since the Lenses are not designed to defuse the light, Unless you are directly behind the car you cannot see them illuminating. I opted not to do the LED swap.

License plate bulbs are not in the 'Bulb Out' circuit.

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'75 Jeep CJ5 345Hp ChevyPwrd, two motorcycles, '85 Pickup: The '89 Volvo is the newest vehicle I own. it wasn't Volvos safety , it was Longevity that sold me http://home.no.net/ebrox/Tony's%20cars.htm

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LED bulbs 700

posted by oldyellr on Sat May 9 11:00 CST 2009
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last visit: Fri Oct 24 14:28 CST 2014

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If the license plate bulbs are not in the "Bulb Out" circuit, why do I get the warning light when I connect my trailer taillight wire to the license plate circuit instead of the car taillight circuit? I thought I had a work-around for using a cheapie harness adapter, but it doesn't work.

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LED bulbs 700

posted by Dave Stevens on Sat May 9 19:08 CST 2009
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last visit: Sun Jan 1 02:36 CST 2012

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As previously mentioned, the license plate lamps are absolutely not on the bulb out circuit. There should be no problem grabbing the trailer tail light (parking light) circuit from the license plate lamp circuit. If the bulb out indicator lights when you do this it is almost certainly an indicator that you've got a trailer ground problem causing the trailer lighting ground to back feed through the brake lamp circuit. Because of corrosion, ground problems with trailers are very common. Ground wires on trailers should be taken right back to the trailer lights and not use the trailer frame as a chassis ground.

Secondly, unless you use some kind of electronic adapter, there is no way to take a four lamp vehicle separate brake/turn lighting setup back into a two lamp combined brake/turn trailer lighting system and have it work properly without upsetting the bulb out sensor when you apply the brakes (for turn signals it doesn't matter -they're not on the bulb out sensor either). If you grab the brake lamp signal ahead of the bulb out sensor (like at the brake pedal switch) without using an isolating electronic adapter, the turn signals would do nothing when the brake lights are on.
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Dave -940's, prev 740/240/140/120 You'd think I'd have learned by now

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LED bulbs 700

posted by oldyellr on Sun May 10 03:35 CST 2009
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last visit: Fri Oct 24 14:28 CST 2014

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Dave, thanks for the explanation and tips! Yes, I do have a solid state adapter to run my conventional dual filament trailer lights off a European and later model circuit with separate indicator bulbs, and that part of it works okay. It just doesn't have the 12 volt feed to fool the Volvo bulb out sensor (those cost $65 in Canada). But I think you've hit the nail on the head regarding grounding. This is a very old trailer that I rewired over a dozen years ago. The lights worked correctly last year when hooked up to my Camaro, but I had to clean and jumper some ground connections to even get them to light with the Volvo. Obviously I need to run a copper ground wire straight back to the lights instead of trusting the rusty old trailer frame, as you suggest. Maybe then the license light circuit will power the trailer taillights without the bulb out warning and I'll only have to contend with that when I use the brakes and flashers. That's not a bad thing because it will serve as a reminder that there's a trailer back there.

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posted by Dave Stevens on Mon May 11 19:52 CST 2009
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last visit: Sun Jan 1 02:36 CST 2012

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Many times over the years I've knocked my brains silly trying to get trailer lights working properly, especially at the beginning of the season, only to find it was a ground fault.

You're slightly wrong in assuming that the cheaper independent bulb trailer wiring converters will upset the bulb out sensor. If you go to the trouble of running a wire for the brake lights all the way up to the front to attach ahead of the bulb out sensor (like at the brake pedal switch) and also grab the parking lights off something harmless like the license plate lighting (not on the bulb out sensor) then all will be well. As I've mentioned many times, the biggest problem with those adapters is that they provide as little as 5 volts through to the trailer brake/turn lamp filaments so they won't be very bright. The proper solution as you know is to use a powered adapter. I know these often cost over $50, even on websites (counting shipping), but if you shop around at places like RV dealers or wholesale auto suppliers you should do better, like under $40 (even in Canada, eh).
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Dave -940's, prev 740/240/140/120 You'd think I'd have learned by now

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posted by oldyellr on Mon May 18 06:37 CST 2009
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last visit: Fri Oct 24 14:28 CST 2014

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Okay, I got around to running a proper ground wire to my trailer lights. Now, when I run the trailer taillights off the car license plate circuit I get no bulb failure warning! So in my case a cheap (free) trailer light adapter does the job. Of course, I only have a pair of simple dual filament trailer lights. I'm sure someone with a trailer that's lit up like a Christmas tree will not be able to get away without using a proper 12v powered adapter.

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