I made a boo boo when I connected up my wiring last time the motor came out. Burnt out the points on the dissy as I connected 12v direct to them. Easy fix and no gib deal, BUT I also connected the tacho send wire as well... Now this one seems to be the non loop type. I need to double check this, but im 99% sure its the single wire type(whatever you call that). Of the eletrical type peoples, does anyone have a good idea as to what it would be that I have stuffed inside. I can do most electrical type stuff, but this is a little past me to fault find. Any clues from the smart electronicy peoples would be great. I'd like to have a crack at fixing it myself rather than paying silly $ to get repaired.

Cheers
Aaron

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If you don't want to take it to an Instrument Repair Shop...find someone with the same Tacho fitted and ask if them if you can check yours by disconnecting theirs and connecting yours...some people may be very reluctant to do so (for obvious reasons!)

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"Show me the Mini!"

Nothing, it will work fine.

When the points are open, the voltage on that single wire rises to twelve volts.
When the points close, the coil voltage drops dramatically to near zero volts.

Putting 12 volts onto the points shorted the points and melted the wires, but the voltage on the tacho at worst still rose to 12 volts like normal, so no damage. More likely cos it was a short, it never wavered from near zero volts.

The tacho doesn't really consume current, it just counts the pulses.

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SooperDooperMiniCooperExpertEngineering

All garage work involves equal measures of enthusiasm, ingenuity and a fair degree of irresponsibility.

Interesting Mick. It's not doing a lot of the rev counting behaviour now though. Give it a tap and it jumps, but nothing much else. I'll look into it a bit more over the weekend. Perhaps the Tacho is ok and there is a melted wire somewhere maybe.

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Have you pulled it apart to check it out??

Probably doesn't help but I have pulled a couple of GT tacho's apart (same principle) and the wire inside (the large white wire, which I think is the loop type - by your description). but it was fried I don't know how or why just was.... I need to replace the wire.

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Not as yet. But I will when I have the chance. I'll double check the wiring to the tacho first. Then I'll go from there.

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even if it is a charred mess full of dead shorts inside?

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"Show me the Mini!"

Well the short was between the 12 volt supply and the points, so mooocho current passing down through the wire to the points.

The tacho is just a sense line, it rises to 12 volts every time the points are open, so if it was going to melt it would do before now. It has a high impedance termination, so current doesn't short through the tacho to ground. The condensor will also absorb the high voltage from the sparking as well.

If there is damage, then it is/was an induction loop, not a voltage sense.

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SooperDooperMiniCooperExpertEngineering

All garage work involves equal measures of enthusiasm, ingenuity and a fair degree of irresponsibility.

I love the smell of burning V90 PVC insulation in the morning

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"Show me the Mini!"