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MG MGB Technical - 65-67 Tach Wiring

I've put a 5-main engine in my MGA and have an early 'B 4" electric tach. Unfortunately, the white loop is missing. It has the terminal and knurled nut, but nothing else. Any suggestions on how to get this working? (pictures are a plus)
Kemper

Hi,

The white loop that you are missing is just the wire from the ignition switch wrapped around the terminal, nothing special.

See attached image which gives you the circuit and an illustration of how the wire wraps around the terminal. NOTE that the direction the loop is wound is important, otherwise it won't work.

HINT: Make sure that the tacho is compatible with the polarity of your car, it should be printed on the face of the dial.

Some reference materials

www.classictiger.com/techtips/motach.html

www.mgexperience.net/article/tachometer.html

this article also briefly outlines converting the polarity of the tacho.

Herb

Herb Adler

How do I attach the wiring? Here's what I'm dealing with:

Kemper

There should be a small nylon block which the loop goes through. It fits onto the post under the knurled nut, as per Herb's diagram.
Dave O'Neill 2

That's the problem, there is no nylon block; just the knurled nut. If I'm not mistaken, the loop and block are part of the wiring harness. Anyone have a spare loop, block, and the bracket that goes over the block?

To get the MGA sorted, I may have to go with Plan B: take an old MGA tach and put the innards from a midget tach inside.
Kemper

The plastic block is just a former for a single turn of wire, shouldn't be difficult to make one from wood at the very least. The bracket is ferrous metal to complete the magnetic circuit, and should also be fabricateable. The loop is just a length of wire. Originally part of the main harness it was changed to a short bulleted ended loop, then the pickup was mounted internally and there was a male and female bullet on the case back.

Alternatively use a voltage triggered tach which are easier to wire anyway, late American MGBs had 4" versions, albeit with Smiths instead of Jaeger if that is what you wanted.
Paul Hunt 2010

This thread was discussed between 27/06/2010 and 28/06/2010

MG MGB Technical index

This thread is from the archive. The Live MG MGB Technical BBS is active now.