[Mgs] tachometer with electronic ignition

[PaulHunt73]

Where are the coil and CSI picking up their 12v supplies from?


The RVI tach is current triggered and wired from the ignition switch 
(not the fusebox) though a pick-up on the tach to the coil +ve and 
pulses through the coil register on the tach.


Prior to 1973 and the RVC tach electronic ignition systems usually needs 
to be powered from the white at the fusebox as the additional current 
from the electronics flowing through the tach pickup can cause 
problems.  However they usually read too high in that case.


FWIW RB cars with ballasted ignition systems also need electronic 
ignition to be powered from the white at the fusebox even though they 
have an RVC tach as the coil +ve is continually switching between 12v 
and 6v and that can confuse the ignition system.


But it sounds like the problem may be more with the tach itself, they 
can be tested if you have an old-fashioned trickle charger as described 
here http://www.mgb-stuff.org.uk/gauges.htm#tachtest


PaulH.





On 09/06/2023 10:24, R. Martin Rogovein wrote:
>
> Hey all,
>
> After 15 years of staring at it in it's parking space, I am almost 
> done with a full mechanical restoration of my 70 B.
>
>
> Engine, overdrive, brakes, steering, suspension, carbs, and more all 
> completely rebuilt.
>
> Loads of new parts.
>
>
> No paint and bodywork yet, but I'll get there.
>
>
> Replaced the points ignition with a CSI electronic unit, wired 
> everything up per their diagram.
>
> Car runs great, but the Tachometer registers nothing.
>
>
> the tach is the RVI unit with three connectors (M and F bullets for 
> 12v from fusebox through tach to coil) and a tongue for switched 12v 
> to the electronics. Ground is though one of the mounting bolts.
>
>
> Is there a wiring trick to get this tach to work with electronic 
> ignition, or do I have to either get a later tach or order one of the 
> conversion boards?
>
> (like this https://spiyda.com/smiths-rvi-rvc-conversion-board.html)
>
>
> thx
>
> -- 
> --------------------------------------------------------
> Israel is the most dramatic country in the world.
> Everybody's engaged. Everybody argues.
> When I leave Israel, I get a little bit bored, you know?
> --Shimon Peres
> --------------------------------------------------------
>
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