How to fit rear parking sensors to an Alfa GT without removing the bumper.
Having bought some rear parking sensors (4 Sensor) from Ebay for £15 I thought surely someone will have written a how to on fitting. But no…so I guess someone had to do it.
1. Remove plastic trim inside of boot covering rear valance by removing all 4 hex screws and the 2 phillips screws under the removable covers.
2. This will reveal the cable entry hole and grommet to the rear of the vehicle. Remove the grommet by pulling it inside the vehicle, we’ll worry about that later.
3. Remove the 3 torx screws underneath the bumper, this will free up just enough slack to squeeze your fingers in the gap underneath.
4. Cut 5ft of electrical wire (5amp or similar), feed the wire through the grommet hole downwards keeping a foot of wire in the car. Lay on the floor and put your hand underneath the back of the bumper and feel for the wire. Pull it free and stick each of the wire together to make a loop using lecky tape.
5. Measure where the holes are to be drilled. You MUST stick to the locations that sensors are setup on Cloverleafs. There is a small amount of scope for variation but be particularly accurate with the two centre sensors as these need to be pretty much spot on. The 3 pictures below will help gauge where to drill the holes. There is nothing behind the side sensors as you can tell by putting your hand behind the bumper.
6. Before drilling make sure the bumper is clean, you mask up the area to drill, clearly marking where to drill and measure, measure, measure, you only get 1 shot at this, if you mess it up you only have yourself to blame. One good measurement is from the floor to the sensor. Mine were 50cm on a flat surface from centre of sensor to floor but obviously it depends on suspension etc.
7. Carefully drill the 4 holes using the drill bit supplied with the sensors. Drilling holes in your pride and joy goes against every natural instinct but take your time and if in doubt seek a second opinion on the markings.
8. Once you have drilled the 4 holes now comes the difficult part. Getting the cables through. If you look at the picture below of a GT with the bumper off it gives you an example of what you have to navigate around. Those black things are actually high density foam. Think of the holes you drilled as A,B,C,D from left to right
Hole A requires you feed some stiff 3 core cable over the top of the foam, I found the easiest thing was to tape about 1ft of ribbon or similar material to the end of some 3 core cable, then feed it through. Once through tape the sensor cable to the end and pull it right through. The ribbon is to give you something extra to feel for at the bottom of the bumper (behind) when you’ve fed the cable through and it won’t snag on anything in the process.
Hole B is the trickiest, I used a single strand of 3 core cable, feeding up the provided conduit and manipulating it over the top of the foam and back down. I also taped a piece of ribbon to this cable to assist with fishing for it.
Hole C is easiest, simply feed it through and it will drop down where you can grab hold of it.
Hole D again, quite easy, just use your stiff 3 core cable over the top of the foam with the ribbon attached again.
9. You can actually see the foam at each side if you lay under the car so it’s not all working blind. With all of these holes, once you’ve got your guide cable to the target position then just tape on your sensor cable, pull it through to where your single strand wire is from section 4, then tape the cable to the section 4 wire and feed it up through the hole in the bodywork. Now you realise why we looped the wire in section 4. It saves you having to fish for your trace wire 4 times over. Makes life much easier doesn’t it.
10. When all the cables are in place you can then connect the sensors to each of the cables and push fit them into the holes you drilled.
11. Cut a hole in the grommet being careful not to take your fingers off in the process.
12. Feed each cable through the grommet and into the boot area. Re-fit the grommet, its tight but not too difficult, just make sure you don’t push it right through the hole else its bumper off job !
13. Position the control unit accordingly in the boot area. Position the speaker accordingly (I stuck mine into the wheel well and it can be clearly heard from within the cabin).
14. Take the power for the unit from the cables running behind the plastic trim you removed :
Don’t bother trying to confirm the cabling by checking the colours going into the reverse light. There is obviously a connector somewhere in between which swaps the colours over as I found out during the wiring process. I used a military in line splice then taped up accordingly. Feel free to use scotch blocks or whatever floats your boat, if you use scotch blocks in line with the hole in the rear brace it will fit behind the plastic cover.
15. Plug power into control unit, put vehicle into reverse with ignition on but engine not running and walk around the car checking the sensors react as anticipated. Any issues can be ironed out here and now before putting the car back together.
16. Put all the trim and bolts back exactly as they came off the car and marvel at your work.
Have fun (Any problems with links just shout up). I also created a word doc I can send over if required.