Rvc rev counter

rich777

Member
So just replaced rev counter with rvc one was rvi as the car won't start now I have 1 spare wire behind dash for rev counter where should the go
Thanks
Rich
 
This may or may not be relevant to the problem, but it's not necessary to change to an RVC rev counter when fitting electronic ignition. You simply feed the power to the ignition module directly from the ignition switch rather than from the coil positive (assuming a negative earth car). The existing wire to coil positive, which passes through the RVI rev counter on its way to the coil, stays in place.

I've done this with two P6s and the rev counters have worked perfectly. Hope this helps.
 
DISCLAIMER: I'm not responsible if your car catches fire....

Probably because you have no power to the coil. The RVI old tacho was wired in series with it.

The RVI will have a white wire which is +12V ignition and a white/yellow wire to the coil via the ballast. Ignoring any illuminator wiring (if any).

For the RVC connect the white and white/yellow together. That's the power feed to the coil on the ignition. On the RVC tacho itself, the +12V comes from the white wire as before. Run a wire from the negative side of the coil to the RVC signal. Connect the black wire (if it exists) to ground.

The wiring diagram is from a chassis A V8. It shows the RVI tacho (63), the ballast in the wire (62), the coil (85 - the other wire from the starter to bypass the ballast) and the distributor (86).

Literally a series circuit through them all from the battery to ground!

1711055346558.png

Later ones (chassis D) are wired differently and are easier to convert.. You'll notice the tachometer sits on the negative side of the coil and there's not the little white bridge wire to feed the power to the ignition circuit. Here you connect the white/black to the white/slate. This also means you have your signal wire for the RVC already behind the dash along with the white wire for power. Which might be why they did it so they could fit either an RVI or RVC with the same wiring loom without an extra wire for the RVC signal as before.

1711056276306.png
 
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Chassis E finally shows the standard RVC tacho (34). The white/black is the signal wire to the negative side of the coil. White is +12V but it powers only the tacho it doesn't feed the ignition circuit. i.e. it is wired in parallel rather than series. It would not affect the ignition circuit at all if you disconnected it, whereas it would with an RVI - which actually removes a point of failure which is a good thing.

1711057388046.png
 
This is extremely helpful. I am ingoing to let my lift down so I can check the chassis number. I will also check if there is any reference to RVI or RVC on the face of the tach.

The wiring diagram you attached matches the one in my workshop manual, but the components have different numbers. My car was one of the first 3500S 's but it was built for sale in Germany. The shop t hat rebuilt my alternator noted that it was German specification. The BW35 trans was also European spec.

I am also going to call MSD Tech Support. Part of my concern is not to cause any harm to the 6AL MSD unit which connects to the coil directly with an orange wire to positive and a black wire to negative.

The newly rebuilt 3.9 engine will not be started until I find some answers to these issues. I promise to post how they are resolved,, along with a diagram of the wiring and some pictures. I will have fire extinguishers handy at first start.



Thank you very much. Keith Hennessee
 
This is extremely helpful. I am ingoing to let my lift down so I can check the chassis number. I will also check if there is any reference to RVI or RVC on the face of the tach.

The wiring diagram you attached matches the one in my workshop manual, but the components have different numbers. My car was one of the first 3500S 's but it was built for sale in Germany. The shop t hat rebuilt my alternator noted that it was German specification. The BW35 trans was also European spec.

I am also going to call MSD Tech Support. Part of my concern is not to cause any harm to the 6AL MSD unit which connects to the coil directly with an orange wire to positive and a black wire to negative.

The newly rebuilt 3.9 engine will not be started until I find some answers to these issues. I promise to post how they are resolved,, along with a diagram of the wiring and some pictures. I will have fire extinguishers handy at first start.



Thank you very much. Keith Hennessee
Further to my last posting, I called MSD TECH SUPPORT. I described the wiring diagram and the tests I had made to confirm that it was correct for my car. I asked if it would harm the MSD 6AL unit to connect the two wires, one from the Tach through the resistor, and the other supplemental voltage line from the starter that supplies power to the coil when cranking to the positive terminal of the MSD Blaster 3 coil along with the orange wire from the MSD 6AL box. He said that should be OK.

I am going to try to connect the small red wire from the MSD 6AL unit to the wire that supplies power from the ignition switch to the starter relay. The large red wire is connected to the terminal on the starter that has the cable from the positive terminal of the battery.

I will post results when it all comes alive.
 
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