Help with disabling bumper sensors when bike rack connected to towbar

[Adrianlle]

Can any of you electrical whizzkids tell me how to achieve this please ? At present I have a simple on/off switch to disable the live feed to the sensor unit( ( a simple Amazon one on a Sprinter with no canbus etc).I would like to disable them automatically when the bike rack is connected to the 13 pin socket. I haven’t checked but I assume there must be 1pln in the 13 pin socket that is not used. I also assume there must be a permanently live pin in the socket. So I wondered if on the bike rack plug I can connect a wire to the permanently live pin ( which on the bike rack plug should be unused ). and then connect the other end to the plug Pin that corresponds to the unused pin in the socket. Then to take a wire from the previously unused pin on th socket and take that to a relay. That would be the live trigger wire to energise the coil on the relay. The other live into the relay would be the existing feed from the on/off switch to the sensor unit. The live output from the relay would go to the sensor unit. It would have to be the sort of relay that passes power until the coil is energised to break the connection-I can never remember whether that is called normally or normally off. It would be quite straightforward to do. The only other thing that occurs to me is that the factory fitted alarm goes off if the plug is disconnected from the socket when the van is locked. Is that a possible complication as I don’t know the mechanism that achieves that!

Is this a mad idea? If so any others?

 

[gus-lopez]

Sounds to me like it should work.

 

[lorger]

deleted as misread

 

[rod_vw]

Don't the reversing sensors automatically disable when trailer electrics are connected? I think my VW ones do if they are wired with the OEM control unit fitted.

Rear fog lights should also be disconnected when a plug is inserted in the trailer socket but the ones on the trailer should still work.

Maybe the solution for the OP is to try plugging in a trailer light board and see if it solves the problem.

 

[2x2camper]

Can you not use a 7 pin trailer socket with a fog light cut out switch. The micro switch would normally cut the power to the towing vehicle fog lights but you could instead route the parking sensor power through it instead.

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[Adrianlle]

Can you not use a 7 pin trailer socket with a fog light cut out switch. The micro switch would normally cut the power to the towing vehicle fog lights but you could instead route the parking sensor power through it instead.

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I don’t think my original post was clear enough. My 2004 Westfalia James Cook is on a Sprinter which has factory fitted Towbar and 13 pin Electrics. The bumper sensors I recently fitted together with an on-off switch. I already have an Atera retractable bike rack with a 13 pin plug. The bike rack does not have foglamps but that isn’t an issue because the Sprinter fog lamp is clearly visible when the bikes are on the rack. The Sprinter fog light does not switch off when the bike rack is connected up. Hence my idea of using the socket permanent live and a relay as an alternative to the dash on/off switch for the sensors ( which I would still retain for extremes like snow etc). The problem with just having a manual on/off is that I have just fitted sensors to the bike rack. I can foresee that when I take the rack off I forget to flick the switch. Then no bumper sensors and then BANG!

 

[Adrianlle]

Done a bit more web searching and whether my scheme stands any chance of working depends I think on whether pin 12 on the 13 pin Towbar socket and plug is unused or not. It appears that on some systems pin 12 is used as a trailer detection system for the Ecu. I can’t think how I might test whether pin 12 is in use with a multimeter so I will have to take the socket off and check. If pin 12 is unused , do you think my scheme will work?

 

[mitzimad]

my sensor speaker is under the passenger seat i just cut one wire and put a switch in it on the side of the seat