12v power to MJ

Rob Heslop · Post by **Rob Heslop** » Wed Jun 13, 2007 7:12 pm

I've connected my MJ up to the ignition so that it is only powered when the engine is running, as I don't like the idea of it being on 24 hours a day. However this proved to be a real pain when I had the car on the rollers as it meant I couldn't make any changes to the MAP when the engine was off which was a bit of a pain. So I was wandering where most people get the 12v feed from, do you use the permanent 12v live or go for a switch supply?

MartinM · Post by **MartinM** » Wed Jun 13, 2007 8:55 pm

You need a supply that is live when the ignition is on and live when cranking:

- the first so that the MJLJ and EDIS is ready to go when the cranking starts
- ...and so that you can update the MJLJ without the engine running

- the second so that the MJLJ and EDIS are powered and can produce the sparks during cranking.

It should be pretty easy to find such a supply from either the ignition barrel or the fusebox

DannyP · Post by **DannyP** » Thu Jun 14, 2007 12:52 am

Power it wherever your old coil was powered from. If in doubt about current handling, use the old ignition to trigger a relay that is hot all the time with a nice, thick lead. Ignition on, MJLJ and EDIS powered, ignition off, relay is off, and so is ignition. On my install I'll be using some Subaru relays and a mounting block pulled from a parts car, one relay for ignition on, two for rev limit, one each for each side of the coilpack, with current limiting resistors.