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MG Midget and Sprite Technical - FIA Battery Master Switch

Hi,

Mk MG midget
Can anyone give me details of wiring an FIA Battery Master Switch. I've had one fitted by a so called motorsport auto electrician but the engine won't cut-out when the cable is pulled. He's kept the wiring so I'm some what stuck.

Thanks
Peter King

The usual cause of this is that the engine keeps running because the electical system is being powered by the charging system rather than the battery, and the kill switch is in the main battery feed. You will need to arrange things so that the feed from the charging system is also isolated.
Paul Walbran

these should help
http://i369.photobucket.com/albums/oo137/mgdavid/misc/DSCN5574.jpg

http://i369.photobucket.com/albums/oo137/mgdavid/misc/DSCN5575.jpg

it's important to work out the two pairs of switched secondary terminals - some of them are embossed in the plastic base with '1' and '2' but done in a way which can be confusing, test it out with a battery and bulb to make sure you have them the right way round.
David Smith

Thanks David, very helpful.
Peter King

Yes as David says the correct FIA switch has 2 sets of "auxiliary" contacts available. The "normally open" pair need to be wired in series with the power to the coil so that when the switch is turned to the "off" position the engine will STOP!

I don't think the electrician has wired these the wrong way around as if that were the case then the engine would not atart when the switch was in the on position.

You need to check what wiring is across these 2 contacts. Equally some people use a battery isolator switch for this purpose however such a switch does NOT have these extra and necessary contacts, have you got the correct FIA switch?
Bob Turbo Midget England

thanks Bob; I meant to add that it took me ages to work out how these switches function, as contrary to expectations one pair of aux terminals are 'on' (closed) together with the master connections, while the other pair is reversed so that the resistor provides a load for the alternator when the main switch is turned off.
*I think*.
David Smith

As said one pair of contacts cut the ignition. I understand the other pair used with the resistor protect the altenator from the sudden switch off in some way.
David Witham

Yes that is correct David the other pair of contacts make when the switch is turned off and this then connects the alternator to a high power resistor to apply a suitable load whilst the alternator is winding down. Not absolutely necessary but good insurance for your alternator if the scruitineer is testing you master switch on a regular basis :)
Robert (Bob) Midget Turbo

This thread was discussed between 20/08/2011 and 23/08/2011

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