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MG Midget and Sprite Technical - Brake light relay

Hi,

took your advice guys and fitted a relay to stop the brake light pressure switch popping again.
Works a treat thanks.
However (there's always a but!) now when listening to mp3 played through an amp there is a crack - it sounds like a pistol shot, every time the brake pedal is released. A friend has said I need a diode?
Anyone any experience of this and fitted a diode (not sure what one is).
Thanks

Jeremy
Jeremy 3

A diode allows electricity to pass in one direction only.

I have a relay connected to my brake lights without a diode and I get no such noise, this is on my 78 midget so I'm not sure about your car.
Rick Bastedo

Maybe you need a capacitor to suppress the arc?

I dunno, I slept through that part of my physics course.
Trevor Jessie

Cheers Rick, Trevor,

I didn't pay enough attention either and am now paying the price!
I'll ty a capacitor - hadn't thought of that.

Jeremy
Jeremy 3

Hi Guys
There is available a relay with a diode built in. I know Hella make them but don't know the part no. sorry.
What is happening is that when you let your foot off the brake and the power is turned off to the relay it discharges like a mini ignition coil giving a backfeed up the line Your local sparky would have a listing in his or her parts cat. Cheers Willy
WilliamRevit

Jeremy - See the article, Brake Light Relay in the Other Tech Articles section of my web site at: http://homepages.donobi.net/sufuelpumps/ to see where to put the capacitor and the size of capacitor to use. I also use a diode to collapse the field that builds up in the relay coil when the brake light switch opens - a bit of extra protection for the switch. Sort of a belt and braces approach. (both the diode and capacitor suppress any arcing). Cheers - Dave
David DuBois

Willy, Dave,

thanks for the info and thanks Dave for the explanation/diagram, relly simple to follow!

Jeremy
Jeremy 3

This thread was discussed between 22/05/2009 and 26/05/2009

MG Midget and Sprite Technical index

This thread is from the archive. The Live MG Midget and Sprite Technical BBS is active now.