Pulsing Daytime Running Lights

I've been living with this for a while, and thought I'd finally post about it. The car is a 1999 Taurus Wagon SE (Duratec).

When I start the car the DRLs light up normally. After about a minute they start to pulse (dim then brighten), maybe every 30 seconds. After the car has been running for a few minutes, the DRLs speed their pulsing up to about twice a second and stay that way.

When the headlights are on, all is well & normal. All other lights are fine. No pulsing, no odd behaviour. All other electrics are fine too.

Is there a relay somewhere for the DRLs? And if so, is it user-serviceable (and easy to get at?).

These symptoms make me think there's a dying relay somewhere; after it's been energized for a while, it starts to go wonky.

I've resorted to driving with the headlights on all the time so other drivers don't confuse the pulsing DRLs with flash-to-pass etc. I was getting lots of stares and they weren't all good. :naughty:

Don't know much about daytime running lamps, could be a faulty drl module, it's located in the left front fender near the headlamp, maybe it's overheating and failing, if that's possible.