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Q & A: Tachometer

Dear John,

I have recently found your website for University Motors Ltd. I would like to both congratulate you on a site written by, and for, MG enthusiasts and to ask for some help.

I currently have a problem related to the tachometer of my 1976 MG Midget.

I have recently purchased a replacement tacho as the previous unit would jam at approximately 3500rpm. The unit I have been supplied with is an RVI2430/00, this unit is does not have the same electrical connections as the previous one, and does not work correctly. This is now the second RVI2430 unit and I am still having problems.

There are three connectors on the rear of the RVI2430/00, a male bullet, a female bullet and a male spade connector. In the dashboard position for the tacho there are three wires, a black ground, a green +12V female bullet and a black/white female spade connector. The black/white wire connects to the positive terminal of the coil and displays a +12V square wave with a frequency of the engine tickover.

I have tried to connect this tacho in the obvious manner of green-male spade, black-tacho securing nut and black/white-male bullet. This configuration shows no reading on the tacho.

My questions are as follows ;-

1) Will an RVI 2430/00 unit work with a 1500 Midgets wiring?

2) Is a voltage stabiliser, or any other piece of equipment required with the RVI 2430?

3) What should the wiring connections be for a 1500 Midget with a RVI 2430 unit?

Any help or suggestions you could provide would be greatfully accepted, as I have now had this problem for a number of weeks.

Regards,

Steven Sloan

STEVEN!

The problem here is that you have an earlier tachometer. Let me explain. The first tachs picked up a pulse between the key switch and the positive side of the coil. The very early units had an external "impulse... read more