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MG Midget and Sprite Technical - RVI Tachs and Electronic Ignition

Continuing to try and advise and help with a '65 Mk. 2 midget that I don't really have time to think about.

I suggested and advised they fit an electronic ignition module to the distributor to save them any points related problems.

They have just had their RVI type tacho' refurbished. As it was all over the place on both the points and electronic systems, then stopped working all together.

Should the RIV tacho work with the electronic ignition, just fit it and go? Googling chucks up various, generally inconsistent, stories. Anything I need to look out for or tricks to have it working as it should?


We have fitted many magnetronic kits and NEVER had an issue.
And why should it be an issue ... The tach is counting the number of current pulses due to the switching on and off each time a spark is to be triggered. Whether the switch us via points or electronic should make no difference.

We also run the original RVI on our VVC K series Midget, simply by having the coil packs powered by a feed wire directly off the ignition switch, and going through the tacho loop before splitting two ways, one to each coil pack. The earth sides of the coil packs are switched by the ecu, just as a distributor electrinic kit would. And it all works fine.

However, I can see a scenario in which there could be an effect. If (as usually recommemded in the kit instructions) the power feed for the trigger is taken from the coil connection the current in the wire through the tacho loop doesnt drop to zero each time, just to the base current powering the module. If the current drawn by the module is high enough it might (very might) confuse things. But I have never noticed it - though we have always used the same unit.

Another issue that can occur with drawing the power from the coil connection is when a ballast resistor is fitted. This reduces the voltage at the coil to 6-8 Volts typically, so can afect the c module's efficiemcy.

For this reason we draw the power for the module from the fuse box.

Paul Walbran

I have a 65 Midget with RVI and electronic module from Simonbbc. It works fine and although a few years ago I dont recall any issues when I installed it. Is it positive or negative earth? I dont see why that should make a difference but mine has been converted to negative and the tacho modified accordingly.

T Mason

Thanks both.

"And why should it be an issue ... The tach is counting the number of current pulses due to the switching on and off each time a spark is to be triggered. Whether the switch us via points or electronic should make no difference. "

Is what I thought...

But then I get some confusing messages about it not working and needing help... I dunno... I will see for myself soon enough! At least now I am more confident that when I come to look at it, I know what I should be going on and that I should work if wired up right.

It is +ve earth, but yeah, I don't see what it would make a difference. Electrons are electrons and wires are wires.


Malc, I only asked about the earth as the module will be different, but I dont think it should make any difference. I may be wrong but I seem to recollect some people having problems with other makes of module and the reason being that the pulses were weaker with electronic and a way to cure that was to put an extra loop round the tacho connection if you have sufficient wire to do it. Never had to try it so no idea if it works.

T Mason

IIRC Willy has the live from an ignition switched live supply instead of from the coil.
Nigel Atkins

The RVI is dependent on a coil current pulse, normally about 4A which drops to zero, producing the pulse, as the points open. With electronic ignition, the coil current pulse will depend on how the solid state sensor (replacing the points) is configured as Paul alludes to Some ignition/ coil combinations might not pulse the RVI tach enough but others will be OK.
Bill Bretherton


what's the cause of the RVC initially needing a tap to get it going?

For a while mine didn't need the tap then later it did again and still does, I can't remember when it stopped and restarted so I can't look up what changes might have happened at those times.
Nigel Atkins


I'm not as familiar with an RVC but sounds like either it has a circuit dry joint, needle is sticking or connections to it are loose. Does the internal light (illumination) work?
Bill Bretherton

yes the bulb works, LED btw. :)

It's the fact that for a time it worked for itself and I thought great - until it stopped starting by itself. If I forget to tap it it don't 'alf bounce the needle.

It's annoying when I want to set the fast idle after starting from cold.
Nigel Atkins

Thanks for all your responses folks.

Turns out the question was moot when I got to take a look last night.

As part of the refurbishment (by SpeedyCables) it appears to be converted to an RVC type, but retaining the RVI face. It explains the confusing messages I was getting about not knowing where connections go etc. No loopy wires required.

A couple of crimp connections and job done and working a treat.


This thread was discussed between 27/07/2021 and 28/07/2021

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