Caution - for the technically minded.
I have a Witter tow bar and electrics fitted to my Passat Estate, which I am very pleased with, except for one minor annoyance. The installation I’d purchased didn’t disable the parking sensor fitted to the Passat. Consequently, whenever reverse was selected with the van hitched up, the sensor would bleep frantically at me which was very distracting at a critical stage of caravan manoeuvring!
So how do I “tell” the sensor that the van was attached and that it should shut up? I thought a little about this and recalled the days of my youth when I had played with relays when installing a set of air horns to my first car (I won’t tell you how long ago that was).
A relay is a device that allows one electrical circuit to switch another on or off. They are typically used in vehicle lighting applications, for example it’s usually a relay that operates your car’s indicators. A low power control circuit is used to energise the relay which then opens or closes a switch on the circuit being controlled.
A little Internet research established that I needed an SPDT or Single Pole Double Throw type 12V relay, which has a hold open feature. This type has 5 terminals rather than the more usual 4. I managed to procure one from my local auto parts store.
A little exploratory work in the back of the car revealed that it was going to be easier to interrupt the power supply to the parking sensor beeper than to the sensors themselves. Once I was certain I had found the right wire I cut it and crimped female spade connectors to the ends. Next I connected the spade connectors to the relay’s hold open terminals. IE in this configuration the parking sensor should still work when the relay was not energised, it did (big sigh of relief).
Next I needed to identify an appropriate signal circuit that would switch the relay when the caravan was connected. The obvious choice was the reversing light circuit, which would be live when reverse was selected. But I wanted it to be live only when reverse was selected and the van was attached. Now a correctly installed 12S (grey auxiliary) socket has the reverse line connected to pin 1 and, in post 1998 installations, pin 2 and 5 are spare. In pre 1998 installations pin 2 is available for auxiliary battery charging, ie it is live when the ignition is turned on; pin 5 is still spare. On my car pin 2 was wired up so that both pre and post ’98 vans could be towed.
As our van is a post ’98 model my solution was to use the pin 2 (blue wire) to energise the relay. First I disconnected it from its existing live terminal, then extended it (with a scotch block and extra lead) and connected it to the relay’s energise terminal, the other energise terminal being connected to ground. Then, by bridging pins 1 (reverse) and 2 (spare) in the vans 12S plug I could create a condition whereby the blue line was only live when reverse was selected and the van was attached. This would energise the relay, thus opening the relay’s contacts and disabling the parking sensor beeper.
Once the modifications in the car were completed I tested the installation by turning on the ignition (but not starting the engine) and selecting reverse. A reassuring beep told me that the parking sensor was engaged. When I walked round to the back of the car the parking sensors detected me and set off the beeper, which was as expected. I then connected a short wire across pins 1 & 2 of the 12S socket. Eureka it worked! The relay instantly energised and silenced the beeper.
All I had to do now was apply the bridge to the caravans 12S plug and the job would be a good ‘un!
Having thought a little more I realised that I should probably have used the number 5 pin as that is also spare on pre 98 vans, hence there should be no problem if either type of van was towed. I will let you know how I get on…
Disclaimer - if you attempt to carry out a similar modification you do so entirely at your own risk.
I hope this is of use to some of you.
Kindest regards
Ian
Post last edited on 04/04/2006 21:34:05
Post last edited on 04/04/2006 21:37:05
-------------
Ian & Fiona
|
Topic: Disabling Your Reversing Sensor
![[:o)]](https://www.ukcampsite.co.uk/chatter/forum_images/smiley20.gif)
