Indicator bulb warning detector circuit

[vexorg]

Bit of an odd one, randomly the indicator flashes fast as if a blown bulb warning is there. Every time we check all the bulbs are fine. I've cleaned the bulb contacts and still randomly it was doing the fast flash.

MOT time a few weeks ago and it failed on rear sidelights changing brightness when indicator or brake came on. So fixed that by attaching a heavy earth wire from light loom earth to the body - lights were fixed and not a flicker from the sidelights now. MOT passed with perfect lights.

The random indicator still happened, but we've since found that the fast flashing happens when the indicator is on and brake pedal is pressed. So, the question is, what detects and controls the fast flashing fault condition?

Where or how does it sense a bulb out?
And what unit decides to make the indicator flash fast?

 

[Mika The Finn]

G'day!
Rear light clusters in the back, there is a metal 'circuit board'. I had a problem, brake pressed, turn signal to the right.
Whole rear was dimly flashing, fixed by adding to both sides, ground wire from metal 'circuit board' to ground/body = under tail light screw!

 

[vexorg]

I had sorted the dimly flashing with the earth wire on the loom at the connector. It's a heavy wire in to the body right beside the lights.

What was now concerning me was if the return earth wire from the lights somehow acted as the bulb fail detect. I doubt it, but can't think of what would be the issue if the lights are ok.

 

[RobinC]

We had a situation a few years ago when we set off on a journey and one of the indicators started doing a fast flash, so we stopped at a Halfords and got new bulbs, and then later - when over taking a lorry on a motorway - the engine appeared to be pulsing with the 'beat' of the indicators, which was unsettling. Stopped at the next services and called the AA, they couldn't find anything wrong but said it was probably a bad earth - problem didn't reoccur while they followed us for many miles. Later I ran a 'fresh' earth wire from the rear light cluster to another earth point, just in case, and never had the problem again.

 

[novocaine]

There is no bulb fail detect circuit. There is no canbus on a k12 that connects to the lights in that way.
The relay works on the amps drawn from 3 bulbs (about 1.2 amps) , when one bulb goes out the amps drawn goes down and the lights flash quicker. (There's a bit more behind this as it's to do with the resistance, but this description is good enough)
You have an earth fault, meaning the cluster is bypassing the bulb (which may still flash only not as bright) and the relay runs fast. Clean up all contacts and check earthing across the back.

 

[vexorg]

Thanks, I know how a conventional system works, was just thrown by it appearing to be fine every time the bulbs were checked.

I found the real fault, dirty connection on the earth pin on the plug to the lights. Moving the connector created an intermittent fault. Cleaned up the pin and all good now. The earth wire fix probably wasn't needed but wont do any harm.

 

[Mika The Finn]

I use dielectric grease in all my vehicles, Harley Camaro & Micra, connectors bulbs and fuses!
Less problems in the long run!...