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MG Midget and Sprite Technical - Tacho wiring

Hello all. We've converted my 67 midget from positive to negative earth as part of the (now nearly completed) 16 year rebuild but can't get the tacho working. It is a negative earth tacho but we're not sure how to wire it up correctly. It has three terminals, a male bullet, a female bullet and a spade. We have a white to the ignition and a white to the coil but we're not sure which goes where and what goes on the third terminal.

Can anybody help please?
WC Mexson

WC

sounds a bit formal :-)

I'm Bill

anyway the spade connection should have a 12v supply when the ignition is on

this operates the electronic circuit that counts the revs

The male bullet should have a corresponding female bullet that just plugs in to it (white wire, rubber protected terminal)

and the female one should have its corresponding male one on a white wire.

The white wire with the female bullet connector comes off the ignition switch, it has the rubber sleeve around it in case the wire drops off the tacho (it happens sometimes, honest!) if it drops off it has protection against short circuits behind the dash. Its corresponding white wire with the male connector has no protection becase if it drops off there is no "live" terminal, the white is on its way to the coil to power up the spark switching circuit when the points close at the end of that part of the circuit.

so

ignitionswitch---tacho wire female_end---tacho---tacho wire male---coil---distributor---pointsandcondenser---earth

hope this has helped
Bill sdgpm

Thanks for this Bill. I'm also Bill and don't know how I ended up with such a formal screen name. I must try and work out how to change it.

I shan't be working on the car again until Thursday night but will try connecting the tacho as you describe. I should have mentioned that the loom is new and doesn't have bullets (male or female) on the whites that we believe to be destined for the tacho.

Thanks again.

Bill.
WC Mexson

Just testing to see if I've managed to change my previously formal screen name!
BillMex

If the loom is new and doesn't have bullets, what car is it for and where did you get it from?

If it is a Midget/Sprite loom, it should have bullets, unless it is for a post '72, in which case it may be wired for the later type tacho.
Dave O'Neill 2

If you have the wires ready to use it should be simple enough to pop a couple of terminal ends onto it, maybe difficult to make the female end fit but the male one will be a piece of cake. Red crimp-on connectors will probably be the way to go.

So remember:
one live off the ignition (Green wire) switch
one White from switch to tacho
one white from tacho to coil

and an earthed casing on the tacho (to let it work)
Bill sdgpm

Thanks again Bill.

Dave, the car is a 67 Midget and the loom was purchased new from MGOC around 15 years ago. A number of "experts" have "helped" with the 16 year rebuild but Dave and Mike (my present helpers - or to be more precise the guys that are now making it work with a little help from me) have had to undo a lot of what has previously been done with more enthusiasm than skill.

So, the cables may have had bullets at some time but don't any more.
BillMex

This thread was discussed between 16/02/2009 and 17/02/2009

MG Midget and Sprite Technical index

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