Problem with indicator when headlights on

Not_Me_Officer

Car is an X plate Golf and recently if the lights are on (side or dipped) and you indicate then at the rear the rear light to say the headlights are on also flashes - so the indicator and rear light flash alternate. It only does it if the headlights are on though. Occasionally the clicking for indicator sound will speed up.

Any idea what the cause of this may be?

Mr.Generous

I've seen funny things happen when the bulb has a short across the terminals. Take out the bulbs one at a time on front and rear lights and while each one is out test and see if it still happens. On my car many years ago (a Ford Escort no less) it was carbon build up on a brake light bulb. On modern car wiring one fault can cause all sorts of other symptoms because the system shares wires. Give it a whirl, If I were you I'd start with the indicator bulbs.

Not_Me_Officer

It's funny because i recently changed one of the rear bulbs. It was either a brake bulb or for the headlights (tail lights, whatever they're called) i can't remember which. It seemed to happen after that but it was the correct type bulb.

Mr.Generous

Bingo its got to be the bulbs!

Geoff1963

Does it only have this problem with one side of indicating ? The side with the new bulb maybe ?

The usual problem is someone fitting a 21 Watt brake-only bulb, when it needs a dual filament 21W + 5W brake + tail bulb.

I think it's a legal requirement that if an indicator bulb fails, it has to flash at double speed. it will also do that if the wiring is wrong in certain ways.

The other possible cause is that you've lost the earth for the lamp cluster on that side. When the lights are off, the indicator gets a ground back through the side lights. When the lights are on, it can't.

Using an assistant, check which rear bulbs light up when you select : sidelights, brakes, reverse, indicators, and all 15 combinations. Check both sides, and make a note of what is on when it should be off, and off when it should be on. That will say what's wrong.
Side only
Brake only
Reverse only
Indicators only
S + B
S + R
S + I
B + R
B + I
R + I
S + B + I
S + R + I
S + B + R
S + B + R + I

Next is to try taking out from the bad cluster, all the bulbs but 1, and checking that function. ( 4 tests )
Now put just 2 bulbs in, and check the 2 functions. ( 12 tests )
Now put 3 in etc.

You'll probably find that some functions only work ( or only don't work ) when a supposedly unrelated bulb is fitted / removed, or switched on / off. If you can identify the pattern, that's the answer.

Good luck, Jim.

AdrianC

It's probably earth to the cluster.

custardy

AdrianC wrote: »

It's probably earth to the cluster.

Yup,poor earth would be my first check.

Richard53

Geoff1963 wrote: »

The other possible cause is that you've lost the earth for the lamp cluster on that side. When the lights are off, the indicator gets a ground back through the side lights. When the lights are on, it can't.

This was my first thought. Very common on an older car.

Not_Me_Officer

I was in the car myself tonight and noticed that when my wife indicated left (it only seemed to happen when indicating left) it would double click (or at least click faster) and then go back to normal. Sometimes it would go faster, normal followed by faster again.

I'd read the replies on my phone on my dinner break but couldn't remember my log in details to respond. When we parked up we noticed only 1 reverse light was on also and when she put it in reverse the indicator bulb illuminated but didn't blink (on the problem side).

So i disconnected the wiring before plugging it back in making sure it was seated real well.

Put it in reverse and both lights lit up this time. Indicator on and it worked as it should.

Fingers crossed that when i just replaced the bulb i just didn't plug in the connector properly. Thank you for the replies. I'll be back if this hasn't worked Hopefully it has though.

Geoff1963

Sounds like the earth wire on that side has got dirty or corroded. When any bulb(s) operate, they get a ground through whatever isn't on, so the "other" bulbs come on a bit. The double rate flash is when an indicator bulb isn't working, so if it's partly on, it will be border-line.
Probably worth plugging and unplugging the cluster on the other side too, clean it up.

The car was probably designed for 10 years, so X-reg is almost double that ; I bet "when 130 years old you become, look as good, you will not, huh ?" ( sorry, Yoda )