Ok, what gives

I was given a tacho - wired it up as the 'giver' said, but the needle bounces around all over the place. Maybe this is why he gave it to me??

When I was installing it, I was poking about under the bonnet, had my multi-meter with me, and was checking the voltage...........I am getting a reading just by waving the -ve lead around the engine bay.

Engine is running ok, but this has me very confused. Any thoughts??

Hooroo

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Rod
http://smg.photobucket.com/albums/v607/Rodney/

Mine 1275LS tacho used to do it, but no anymore, well not so much.

Not sure why, but I have played with the igntion heavily since then. SO I think that has a lot to do with it.

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1964 Morris 850, 1330 Supercharged - 81.8hp atws.
1975 Leyland Mini S 1100S powered - Nice and reliable.
1977 Leyland Mini LS - Project LS-T

On New Zealand GT1275s the tachos bounce mine does it and i have others do it too

Look for half arsed connections on the way to the tacho(you have probably allready done this) but other than that it may be after 40 years it has a few degraded components (Like germanium transistors for instance). Loose connections will generate little back EMF voltages that will upset the tacho.

As for the multimeter, don't worry too much about it. They are so sensitive that they will pick up all kinds of spurious voltages. One trick for the new boys in the work shop is to convince them that if they put a lead on each temple and think REALLY HARD then they will register a voltage. The idea you convince them of is that the smarter or harder you think, the higher the voltage measured.....

Then convince them that a Megger Insulation Tester operates like a lie detector, ask them a question while they hold the two leads and then ZZZZZZAP them with 500 volts. The resistance reading will tell if they're lying or not you see....

Good fun to watch.

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SooperDooperMiniCooperExpertEngineering

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

I bought a speco tacho the other day, did a quick trial in the engine bay today and reading was smooth over 2000, but jumped around abit under this.

I'll pull out the destructions in the morning, it did have a section dedicated to mini's! and the possable need to fit an extra part - something crazy like a 30amp diode - can't recall.

Are you using a mini tacho or aftermarket?

In the case of my engine, I'd say points and worn dizzy wouldn't help the cause, but the soon to place pulsar should fix this.

It's an 'after market' tacho. I'll play with the various connections again too I guess.

Cheers

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Rod
http://smg.photobucket.com/albums/v607/Rodney/

yeah theres something suss if its bouncing, deffo shouldnt do that.