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MG Midget and Sprite Technical - Tacho's and Pertronix...

Hi all,

Question for you knowledgeable chaps on rev counters. I've just fitted the pertronix Ignitor setup and have, as expected, some issues with the rev counter fluctuating significantly. Having trawled the archives, I understand that the earlier tacho's, like the one on my '72 midget - RVI 2430 - arew prone to this. However the later ones aren't. I've got an RVC 2415 to fit in it's place but the wiring connections are different. ie. the RVC tacho is a connector short. Where the RVI has one white wire in & one out, the RVC only has one (from coil & to ignition switch).

Can anyone advise how I can rewire to use the RVC one?

Car is standard negative earth & doesn't have a ballast resistor.

Thanks, Matt
Matt

Matt,

This is the first time I've heard of someone having this problem other than myself. My old electric Smiths counter of unknown vintage in my negative earth 59 Frog died so I bought a new Smiths to replace it. I also have a Pertronics and this counter does strange things. It shuts off for a few seconds and comes back to life or suddenly jumps to 7000 RPM and just sits there for a while. Or it spins all the way around back to the peg. When it first happened, I sent it back with an explaination, they changed the stepper motor and it still did it. Sent it back again and they sent me a new one and it still does it. This led me to think that it was not the tach but the Pertronics causing the problem. I've been meaning to call the supplier here in the US to see if they have an answer.

I can't help with wiring your new counter but I'm curious to see if anyone has any recommendations on the odd behavior. If I get an answer from the supplier, I'll definately post it.

Martin
Martin

Thanks Martin.

This seems to be a fairly common problem with these. There is a lot in the archives and the answer is to fit a later model tacho that isn't the inductive loop type. I've worked out how to wire up the later RVC version I have but the only thing I hope someone can help with. Which terminal on the coil do I wire the supply to the tacho to? I think it's the -ve but not sure! Fingers crossed.... Matt
Matt

The white wire from the Tacho goes to the positive of the coil, although will work happily for many thousands of miles if inadvertantly wired the other way around
Bob (robert) Midget Turbo

On later cars, the pulse wire is white & black and connected to the CB or -ve side of the coil.
Dave O'Neill 2

Thanks all - I connected the new feed to the RVC tacho to the -ve side of the coil and it worked perfectly - no problems. It seems the later 1275's ('73 on, I think) have it on the -ve terminal, although the RVI one I took out was connected to the +ve side. I just joined the original white wire from the coil to the white wire to the ignition switch after unplugging them from the old tacho - then ran the new feed directly from the coil. ie. the black&white pulse wire Dave mentions.

Cheers, Matt
Matt

I've just purchased a quite nice '66 GAN3 for my dtr. However in getting it ready for inspection (I bought it in NY), I was unable to get the rev counter to work. A little more inspection, showed that the car has been converted to - grnd.

We want to install a Pertronix unit ASAP and of course will get a neg grnd unit.

Short of sending the rev couinter away to be re-built, does anyone think that the conversion to - grnd is a cause of the rev counter not working?

If so, can the rev counter be converted to work w/o sending it away?

Gord Clark
Rockburn, Qué.
Gordon A. Clark

Gordon,

Yes, the positive ground rev counter in a negative ground car won't work. You could try reversing the wires that go into the rev counter and see if that helps. That's how I ran my + ground counter in my - ground Sprite for about 4 years until it gave up the ghost. That's when I bought a new Smiths counter.

Martin
Martin

on the back of the 72 midget tacho (RVC type) there is a spade treminal and a bullet terminal , which one is the coil connection ?

I assume the shell is earthed via the alum knurled nuts on the fixing posts .

This is going into a -ve earth dynamo charged Frogeye.
TIA thanks Alan
AP Jones

This thread was discussed between 26/07/2008 and 08/08/2008

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