I fitted a towbar to the GT (07 Blackline JTDm) today which was an absolute pig of a job to do, so to (hopefully) save everyone else some agro, I thought I’d do a guide to it.
This is for a Thule/Brink removable towbar though the fiddly bits (removing the trim and drilling the outermost holes) will probably apply to all towbars.
Removing interior trim
To remove the spare wheel well cover unscrew the 4 load tie down points, they are a 6mm allen key, and prize out the central retaining plug with a large flat head screwdriver. Remove the tool tray, spare wheel etc.
To remove the panel forward of each cubby hole there are 3 screws, you need to fold the seats forward to get to 2 of them. Pull the panel away gently, and unclip the wiring (12v plug on one side, boot light on the other).
To remove the C-pillar trims pop off the “airbag” cap (the clip will separate from it so try and catch it!) and unscrew the 5mm allen key screw behind it and pull out (there are 3 push fit connectors which will release with a bit of a tug) and leave hanging on the seat belt lug.
To remove the side cubbyholes there are three screws within each cubby (2 at the back, 1 at the top), and two screws which were behind the C-pillar trim.
To remove the boot lip trim there are just 4 5mm allen head bolts and 2 crosshead screws.
If you have Bose audio remove the subwoofer, disconnect the plug, and unscrew 2 crosshead screws at the top, and 2 10mm bolts at the base.
Once the trim and subwoofer are removed rotate the side carpet (still attached at the front by the rear door/side cards) round, and pull out the sound deadening linings to expose the rear corners of the car.
If you are being really fastidious at this point scrape away any sound deadening from beneath the internal mounting plates, mine sat evenly on top of it so there was no risk of distorting the boot floor when torqueing everything up, so I left it.
Mark and drill the holes; this sounds simply and quick enough but was the biggest nuisance of the whole job. The rear haunches make getting a relatively normal sized battery drill into position difficult. There is already one hole for the rearmost bolt that goes through the chassis-rail on each side, but it is in the wrong place.
The Thule towbar I’m using has inserts that go through the chassis rail to prevent crushing it, and require a 25mm hole in the top of the chassis rail. Drill the holes from the top, add the inserts and drill the forward hole through the base of the chassis rail. For both sides in turn temporarily bolt up the nearside spreader plate as a template to the underside of the chassis rail and drill the rear hole for both sides. On the nearside there is a thread which projects down from the chassis rail at exactly the point where this rearmost hole needs to go. I removed the fog light (3x 10mm screws and 1 phillips) and it’s little heatshield so I could get the angry grinder to the thread.
While the grinder is out cut the inner rear corner out of the subwoofer mount so that it doesn’t foul the inner towbar mounting plate.
With all holes drilled bolt up and tighten 4 spreader bolts on the offside, and loosely mount the main crossmember to the offside through chassis rail bolts. At this stage you won’t be able to get it into position, but lift it as far as possible (until it hits the underside of the bumper) and mark the bumper cut. Remove the crossmember and cut out the bumper cut, I used a set square on the leading edge of the bumper and a Stanley knife which went through with a bit of patience.
Fit the cross member, receptacle for the removable bit and electrics mounting plate and torque everything up.
There is a very good guide to building your own relay based system here
I have broadly followed that, but using a relay box like this
mounted on the offside as there is more space away from the subwoofer, and run a feed around from the 12v socket on the other side of the boot.
I've put the fog light on a relay and left the tail light fed from the car loom on the basis that a fog light bulb is 21W and the 2 taillights are 5W each, but have left the option to swap them over incase I ever tow anything with loads of side marker lights which are also fed off the taillights.
That’s it, test it, put the interior back together, and put the kettle on.