Retro-fitted parking sensors yesterday, including a relay to stop beeping when moving through R on auto gearbox. Relay needs a live feed, taken off boot light supply.

All fitted and tested satisfactorily, locked car, went to bed reasonably happy . Unlocked car this morning, switched on ignition, horn started beeping. Tried relocking/unlocking car, same problem, several times. Very embarrassing for me, very annoying for neighbours (especially the one on nights!). Horn stops when ignition turned off again, and stops when engine started, but so far haven't driven car anywhere. :(

I guess problem must be something to do with parking sensor wiring, anybody got any (sensible!) suggestions please?

Is it an official Skoda reversing sensor kit for the New Octavia?

Noop, it's a quanan 4 sensor kit with additional relay. Worked fine when tested/fitted, ignition/engine on/off - but that was before I locked the car/set the alarm!

I'm guessing that the relay holds off the sensor kit for a second or 2 when you enter reverse thus preventing the kit turning on when you pass through R on the auto box. The kit itself I imagine is powered from the reversing lights. I'm not sure why you need a permanent supply for the relay though.

I'd say the connection to the boot lighting circuit is your problem. It's creating a volt drop of sufficient magnitude on this alarm monitored circuit to fool the alarm into thinking the boot has been opened thus triggering the cars alarm system.

Thanks Johnny. Yes the relay is for just that purpose, and your conclusion is the only one I can think of too. I'll take the relay out first and see if that cures the problem. Unfortunately , as you say, that means the parking beeper triggers when I pass through R, and also means I'll probably trigger the bulb failure monitor circuit. Any thoughts on how best to access an ignition switched feed for the relay?

I did something similar for my mp3 player install last week. It's a hard drive in the boot which boots up and starts playing where it left off when the ignition is turned on. There's a remote controller on the dash and worked fine until I started the engine at which point the audio cut out even though the mp3 player kept running. I then had to re-boot to get it going again.

It seemed that interference between the cars wiring loom and the mp3 player control cable was causing this. I got round it by installing a timer controlled relay which held the mp3 player off for 5 or 6 seconds thus delaying the boot up and giving me time to start the engine before the interference took place.

I did this with a simple circuit using a 555 timer IC, a few components and a relay.

The timer and relay is connected to an ignition switched supply. The relay is closed but as soon as the ignition is turned on the timer opens the relay for 5 seconds and then closes it again.

Why can't you supply your relay from the revering lights circuit though? It shouldn't bring up a lamp failure on your dash. If anything your relay circuit may prevent the lamp failure warning coming up because it places a load on the circuit even if the lamp itself fails.

The best place to get a switched ignition supply if you really need one is from the fuse box on the side of the dash on the drivers side. There's any amount of empty fuse holders of which some are permanently live and others are ignition switched. Just check a few with a multimeter.