This happened a few weeks ago.
My reliable 1999 406Hdi 110BHP developed a niggle after new-year. The
indicators would flash a few times after turning the ignition to
accessory, then go off when I started the car. This strange behaviour
got worse and worse, sometimes having to turn the indicator on to turn
it off again.

After buying the Haynes manual (pretty useless unless you want to
dismantle the engine). Convinced it was some earthing problem I located
the earth points up under the dash in each foot well, tightened but no
real effect.

It all went really bad one day driving 40 miles home down the M3. The
indicator started flashing (left) and no matter what I did could not
stop it, save occasionally holding the stalk hard in and odd position.
Caused real havoc with other motorists and I was a complete stress head
by the time I got home.

Eventually found the control unit, but forget taking it out, or even
removing the connectors, as its behind the fusebox tucked up under the
drivers side foot well.

Eventually took the indicator switch itself off and here I found the
problem. The indicator switch is just a changeover switch with a centre
off position. The off resistance was less than 500Ohms, and this was
causing the electronics to false trigger. I could move the switch around
and get varying resistances, but never more than a few hundred ohms. For
those non electrically minded people, it should be hundreds of MegaOhms,
not hundreds of ohms, on an open circuit. I was tempted to take the
switch apart, but a) it looks expensive and b) looked like there were a
lot of pieces in it, as its the light controls as well. A quick blast
through with some switch cleaner, and now the contacts measure
open-circuit, and it's all been OK since. Phew!

This is definitely a case of modern electronics fouling up. If it were
an old lamp flasher this would never happen.

Robert
Older and wiser