Towbar dash light
 

I tried out my towbar electrics the other day for the first time (dealer fit from new).

All the lights on the trailer worked OK but there was no trailer turn signal indicator on the dash?
This is required by law in the UK (and I assume the US as well?)

Where should the trailer turn indicator be and what does it look like?
I couldn't find any reference to it in the manual?

should be seen on the dash (regular spot for turn signals) and blinking TWICE as fast...

hmmm, not sure what you're asking... there's supposed to be a separate turn signal light on the dash for when you have a tralier hooked up? I used my '01 to tow a jetski for 3 years and never knew or saw one.

There has to be some indication to show that the trailer turn lights are operating. (This is usually an additional light in the dash or buzzer).

The indication may be as drex suggests, that the dash turn lights blink twice as fast. I'll have a look again.

I don't remember anything different happening... hmmm

There is no separate instrument cluster indication of trailer attachment in the US. We have to observe the trailer lights (as you should always do each time you hook up).

In the US the BMW 7 pin wiring harness interfaces with the "Trailer Module" located under the spare tire. The "Trailer Module" senses a connection the trailer and turns off the rear park distance sensors (if you have them). The turn signals operate on the same basis as no trailer attachment. I had a turn signal light fail on my Airstream and my 2001 X5 "Trailer Module" sensed the failure and caused my signal indicater to blink "rapidly" (normal indication of a light failure) just as if a light had failed on the X5.

that's correct. it blinks fast when the module is connected (but no trailer), or depending on the trailer electrics.

have yet to tow a trailer that doesn't blink fast (although all the lights work)...

but there is no extra trailer light on the HUD or its schematics..

Turn signals should not blink fast unless a light has failed. If your turn signals always blink fast when your trailer is attached you have a wiring problem.

My turn signals have only ever blinked fast on a rental trailer with no ground wire. Rental trailers with a ground wire have not blinked fast. It could have been that all the trailers without ground wires also had crummy trailer light sockets, but I doubt it. I always assumed that you can't depend on the hitch ball or safety chains for the ground circuit.

The fast blinking is simply the electronics responding to the high resistance (same as a blown bulb).