Fitting Reversing Sensors

Since I have had to replace the complete reversing sensor and alarm system due to damage to the old system during the February 2009 accident, I decided to make a guide of what’s involved in fitting a system to a Series vehicle. They’re good accessories, helping with parking or manoeuvring in tight spaces, increasing safety (especially where there are children), and making life far easier in three point turns. The latter point was really proven during the Alps trip, where well over a hundred three or five point turns were required on numerous days – the sensors allowed me to use every last inch for manoeuvring up against ledges and hill sides at the end of each zig-zag in the descents without Helena having to get out and direct me every few minutes. Many people dismiss these systems as being for bad drivers or “softies”, claiming they are of no benefit to good drivers – don’t believe a word of it!

The kits comprise an ECU, a number of sensors (2,3 or 4), an audible alarm unit and a wiring harness to provide power and connect the alarm. Some kits also have digital displays, varying from very basic to units which display a measurement of remaining distance and which sensor is detecting an obstacle. My kit does not have the display.

The first thing is to decide where to put everything. I have a 4-sensor kit, and decided to install the sensors on the each end of the tow hitch step and in the rear corner protectors. Holes were drilled in the protectors and special mountings made up to enclose the step mounted sensors, but a simple bracket would suffice. The ECU needs to be positioned within a suitable distance of the rear in order for the sensor cables to reach. I chose to put the ECU in the rear tool locker (109 and 110 only), which is now used as my battery box. The audible alarm was fitted atop the rear lights wiring cover panel (self adhesive tape).

The sensors need their cables threading through bumpers or mounting brackets, and this can be a problem where the plastic plug is so big. I had to enlarge the cable holes in the step mounting tubes to allow the plugs to pass through, using rubber grommets to fill the holes afterwards. The photo shows the cable being pulled through the rear corner protector’s tube section with string.

Once all the sensors are in place, the cables need routing to the ECU. They need to take a suitably direct route to reach, but you don’t want them exposed to damage. In my case, routing them along the top of the rear cross member worked fine, clipping them in place and bundling them with cable ties.

With the sensors and the main harness connected to the ECU, the main harness other ends of the main harness are connected to the alarm’s terminal plug and the power source. In my case, because I have already fitted reverse lights, the feed could simply come from the reverse light feed and earth directly to the battery. In vehicles without reverse lights, or where the system is fitted to the front of the vehicle, a switched feed from the battery will be entirely acceptable.