Where is relay 109 located on a 2003 be beetle 1.9 t.d.I.

Get a service manual, it will help you locate it. Usually they are under the hood or behind the glove box.

replace thermo switch... this is normally located near radiator hoses.

Kneel on the ground with your driver's door open, look up under left side of steering column. Should be able to see black and grey relays, 109 is in the upper row.

I believe you're looking for Relay 109. Look up under the dash on drivers side and you'll find the tray with relays in it. It should have a big 109 on it and be a square relay about 1"x1". It should also be Grey in color. If it's black definitely replace it. The black ones are the older, problematic relays.

Glowplug relay 180; located in Position 10 in the relay panel. If you unplug the coolant temp sensor, you can trick the computer into thinking it's really cold out, and it will run the glow plugs.

You could try www.faxonautolit.com for a used dealer service manual.

CODE P2181 COOLING SYSTEM PERFORMANCE MALFUNCTION CONDITIONS - ECT SENSOR HAS FAILED. 2.0L ENGINE ECT LOCATION IS ON THE UPPER RADIATOR HOSE CONNECTION AT THE REAR OF THE CYLINDER HEAD. 2.5L ENGINE ECT IS ON THE UPPER RADIATOR HOSE CONNECTION ON THE CYLINDER HEAD ALSO.CHECK COOLING FAN FUSE AND RELAYS

Does your glow plug light on instrument panel come on when you turn the key? I'm assuming the car won't start? If no GP light on instrument panel then it sounds like a Relay 109 problem. It's the main power relay. It's a grey or black 1" square relay located under the dash on the driver's side. Give it a smack with a screwdriver or something. You might be able to knock it back into whack. Seriously.
www.tdiclub.com - loaded with tdi info

Relay 109 right? It's under the driver's side dash. It's about 1"x1" and either light gray or black. www.tdiclub.com has tons of useful info!