Last MoT Advisory showed indicator bulbs to have aged and, consequently, were paler than should be. So, I have just replaced all 4 with "Twenty20 Endurance Amber" PY21's ready for next MoT a few months away. Replacing them was easy and they work (although I can't see that much difference...). However, suddenly, and only very occasionally, when indicating right, the flashing speed goes wild..? I've checked to see if there's a blown bulb - there isn't; I've checked to see if I fitted them wrongly and earthing/contact is flawed but there's nothing obvious; anyone got any ideas? The bulb lifespan is guaranteed for x3 years.

Rapid flashing usually means a bulb is not working, the first thing I would do is check all lights when it is rapid flashing and if one is out or dim clean the contacts of that one, if they all seam ok clean all contacts and try again.

Richard FL2 07 TD4 GS Auto
Ex 02 TD4 Auto

Thanks Richard. All bulbs do work - when standing still, using the hazards and/or the direction indicators. It's impossible to make the lights flash faster when the bus is stationary, also impossible to predict when it happens. However, I'll disconnect and reinspect tomorrow as you suggest, just in case I missed something the first time around.

When it happens, can you get out and have a look at which one is not working. At least that'll narrow it down to the faulty lamp. You could try swapping bulbs and if the problem reverses, it will be the bulb. Another thing to do - try them with all other lights working - side, tail, reverse, fog and indicator. If it does it then, it'll be an earthing problem. Past: FL2 TD4 HSE Auto
Evoque SD4 Dynamic Lux Auto
Present: Audi A3 S Line.

+1 for faulty bulb.

I never buy cheap bulbs (not suggesting thats what you have done crocket) as they never last, and I've had a few fail quite early in life. I had a nightmare with some I got from Halfrauds and fitted them to my old D3. Binned them all of in the end and got some decent ones from Advanced Factors. (site sponsors) Updated- Waiting for a Scotland v England 6 Nations home win. 24th Feb 2018
Gone-1972 88 SWB Soft top
Gone-1981 24v FFR Lightweight
Gone-2009 Freelander 2 TD4 GS manual
Gone before it bankrupted me- 2008 Discovery 3 TDV6 Auto
2013 Freelander 2 SD4 GS Auto

I wonder if you can get an LED upgrade for these?

 3 x FL1 2 manual + 1 auto
5 x FL2 4 manual + 1 auto
Now Discovery Sport P250 MHEV SE

Try fleabay, they are probably available with a 10 day delivery from Hong Kong....  Updated- Waiting for a Scotland v England 6 Nations home win. 24th Feb 2018
Gone-1972 88 SWB Soft top
Gone-1981 24v FFR Lightweight
Gone-2009 Freelander 2 TD4 GS manual
Gone before it bankrupted me- 2008 Discovery 3 TDV6 Auto
2013 Freelander 2 SD4 GS Auto

Just had the same thing happen to me on a few occasions as I've been driving along, however when I stopped to get out and look they worked again. Took a while to get it to continue when I had stopped but eventually it carried on and turned out to be the side indicator. The bulb wasn't blown, these bulbs are the push in type so a little tweak of the contacts in the bulb holder to make them tighter seems to have done the trick. 2007 TD4 XS Manual in Sumatra Black

Well, after removing and refitting each of the indicator bulbs, and having given all of the holder contacts a clean (despite them looking fine), my (expensive) bulbs all seem to be functioning as they should. Couldn't understand why all were working, as were all of the other bulbs, and only occasionally going berserk when a turn to the right was made. However, thanks folks for the thoughts.