Extra Ignition power wire

[pharriso]

I could answer if I knew what RCI and RVC mean. The car had been converted to negative ground when I got it. I did not request anything special from them.

The initials are confusing...

RVI is current sensing, as originally fitted, the Tacho has 2 white wires (In & out) & measures the current pulses passing through the wire

RVC is voltage sensing & has a single wire. Although nominally the ignition wire is at +12v there are high voltage spikes, caused by the ignition coil & the tacho senses these.

Electronic ignition often screws up our RVI tachos, so you can fit a conversion circuit board from Spiyder to convert over... I think Nisonger did a similar conversion, that's why only one white lead.

[pharriso]

I see my confusion.

My tach only has two white wires coming out the back. One is piggy backed to the ignition light and it goes to the ignition switch (position 2)

That first wire is used for the ignition / charging indicator. Good

I only have one other white wire which disappears into the potted input on the tach which also comes from the ignition switch (position 2). According to the descriptions I have there should be another white wire exiting the tach and going to the coil.

As I said in my last post I think your Tach has been converted to RVC. In which case that single wire needs to be connected to the coil +ve terminal to sense voltage.

The extra white wire I have coming from the harness has continuity to the coil. Can I simply splice that wire into the wire coming from the ignition switch? .

Yes !! So you have a direct feed from the ignition switch to the Coil

Or, should there be another white wire exiting the tach?

The tach configuration is as I received it from Nisonger.

Please forgive my confusion.

Don't apologise, we've all been there! I would confirm with Nisonger that the Tacho is now RVC & then crack open a beer...

[billwill]

I see my confusion.

My tach only has two white wires coming out the back. One is piggy backed to the ignition light and it goes to the ignition switch (position 2)

I only have one other white wire which disappears into the potted input on the tach which also comes from the ignition switch (position 2). According to the descriptions I have there should be another white wire exiting the tach and going to the coil. The extra white wire I have coming from the harness has continuity to the coil.

Can I simply splice that wire into the wire coming from the ignition switch? Or, should there be another white wire exiting the tach?

The tach configuration is as I received it from Nisonger.

Please forgive my confusion.

It seems that your tachometer is a voltage driven one (RVC) not a current driven one (RVI).

What does it say on the dial?

If this is the case then the wiring diagrams shown above are the wrong ones.

RVC are not the standard option, but are often fitted (or converted from RVI) when electronic assisted ignition is fitted.

They would probably be wired with a wire direct from the ignition switch to the coil, then with a sensing wire (which may have some conditioning components in line), probably white, leading back from the coil to the tachometer.

In which case your extra white wire is probably the old disconnected wire that was used with an RVI tachometer.


Have you actually stated whether your engine actually runs and whether or not your tachometer reads its RPM? Is this all a wild goose chase just because you have an extra wire that you can't account for?

[fattogatto]

The harness is new. The dash is out of the car. So, NO, the engine has not run.

Nor does it have electronic ignition.

Am contacting Nisonger for instructions.

[StressCraxx]

The harness is new. The dash is out of the car. So, NO, the engine has not run.

Nor does it have electronic ignition.

Am contacting Nisonger for instructions.

Hello Charles,
Good idea to contact Nisonger. The tach in the photo does not have the coil wire loop on the back. Nisonger may have built/rebuilt for you an RVC tach. They are not bad, just different. Unfortunately I don't know what to do with the extra white wire either.

Best regards,
Dan Wise

[Billmack]

On the white wire.. It needs to come from the run position on the key switch to one of the white on the tach then from the other white wire on the tach to the coil. That's what lights up the coil. There should also be a green wire to a tab connector on back of teach to power it up. I think I have seen your name in a sportsv2000 forum. I have a Lola 594 and used to work with the pirate SJohnson. The difference between the tachs functionally is one has the loop of white wire inside the tach and two connectors and the other has the similar loop wrapped around a nylon block and completely visible on the back of the tach .

[Billmack]

Originally the tach has one male and one female connector as the electricity has to travel in the right direction to make it work. On the earlier tach some folks have called single wire I usually clip the wire in two places so I can reverse the direction of the electricity if necessary. I hope this clarifies.

[fattogatto]

First of all, thanks for all the replies. I have certainly learned how much I don't know.

Issue solved by a quick phone call to Steve Smith in Florida and reference to the Nisonger documents I found.

Yes, the tach had been modified for a Pertronix ignition system. Only one white wire exiting the back of the tach. That wire needs to be extended (a long way) and connects to the NEGATIVE terminal on the coil. The tach gets its power through the smaller gauge white wire that powers the ignition light.

That left two white wires in the harness. One switched to the key (position 2) and the other showing continuity to the white wire that goes to the POSITIVE terminal on the coil. So, all that was needed was to connect these two wires together.

Voila.

[pharriso]

I like a good ending

[h20hamelan]

Steve is excellent!

[billwill]

On the white wire.. It needs to come from the run position on the key switch to one of the white on the tach then from the other white wire on the tach to the coil. That's what lights up the coil. There should also be a green wire to a tab connector on back of teach to power it up. I think I have seen your name in a sportsv2000 forum. I have a Lola 594 and used to work with the pirate SJohnson. The difference between the tachs functionally is one has the loop of white wire inside the tach and two connectors and the other has the similar loop wrapped around a nylon block and completely visible on the back of the tach .

Nope... What you describe is the difference between early & later RVI tachometers (current pulses). What the OP has seems to have is an RVI tachometer converted to RVC (Voltage pulses).