11 replies to this topic

[Gulfclubby]

My clubby originally came with the twin clocks without a rev meter and I have now fitted the rev meter triple GT clocks, but behind the dash, it's still the old thing so the rev meter currently is not properly connected over the voltage regulator module. Now I could probably work out a way to get it connected over the existing unit for the petrol and water temperature gauge, but that would mean taking the whole dashboard apart again, and after having done that too many times already, I really don't want to. Instead I'm simply going to fit another voltage regulator to the + lead of the rev clock that currently goes directly to the fuse box, which results in the clock behaving totally wrong.

Long story short: does anyone know what kind of resistance or circuit the voltage regulator has? Would someone be able to provide a wiring diagram, so I can reproduce a unit with the same functionality? Advice greatly appreciated.

[Gulfclubby]

Found this: http://home.mindspri...eStabilizer.pdf

Should help.

[Ethel]

The rev counter does not need connecting.

It's just gauges like the fuel & temperature one's that sense resistance that would be effected by changes in voltage.

[Gulfclubby]

The rev counter does not need connecting.

It's just gauges like the fuel & temperature one's that sense resistance that would be effected by changes in voltage.

Thanks for this info. So basically if we hook the tacho/revcounter up to battery for power, the chassis for ground and the coil for signal, it should work correctly? If it does jump up and down erratically, that could be a sign of a coil that is about to go, I have been told. So I will try reconnecting the clock and fit a new coil and see if that helps.

[Dan]

What type of tacho is it? It will say either RVI or RVC on the front somewhere. Early 1275 GTs used a tacho that is basically incompatible with your wiring and if that's what you have, to be able to use it you will have to rewire the ignition.

[Gulfclubby]

What type of tacho is it? It will say either RVI or RVC on the front somewhere. Early 1275 GTs used a tacho that is basically incompatible with your wiring and if that's what you have, to be able to use it you will have to rewire the ignition.

Can't tell you right now as I need to see the car first, probably next weekend only (currently on holiday). Which one would be the one that is working and how would the wiring have to be changed to make it work?
PS: From what I know from afar is that it's a proper triple GT clock unit, so not a Smith gauge or something like that, but I don't know how old it is. Will get back to you next WE.

Edited by Gulfclubby, 08 August 2010 - 06:38 PM.

[Dan]

RVI is the wrong type. They don't connect to the earth trigger of the igniton, they sense pulses in the igniton supply instead.

Can't remember off the top of my head what the 1275GT type looks like. It might have two connections for ignition cables, or it might have a stud with an insulated clamp. If it has a stud and clamp, the supply wire to the coil positive from the ignition switch has to be wrapped around the stud once and clamped up. If it has two connections, the supply must be cut and conneced via the tacho. This means if the (very old, unreliable when brand new) tacho fails, you have no ignition supply. The unit also needs 12v and earth as well as these ignition connections. I don't think that anything else can be connected to the ignition wire without it affecting the tacho.

It will not work, at all, with any kind of electronic ignition.

If it's RVC, it works as you would expect.

[Gulfclubby]

RVI is the wrong type. They don't connect to the earth trigger of the igniton, they sense pulses in the igniton supply instead.

Can't remember off the top of my head what the 1275GT type looks like. It might have two connections for ignition cables, or it might have a stud with an insulated clamp. If it has a stud and clamp, the supply wire to the coil positive from the ignition switch has to be wrapped around the stud once and clamped up. If it has two connections, the supply must be cut and conneced via the tacho. This means if the (very old, unreliable when brand new) tacho fails, you have no ignition supply. The unit also needs 12v and earth as well as these ignition connections. I don't think that anything else can be connected to the ignition wire without it affecting the tacho.

It will not work, at all, with any kind of electronic ignition.

If it's RVC, it works as you would expect.

That is excellent news then, provided I do have an RVC type tacho. I have an electronic ignition, so an RVI unit would have to be removed. I'm quite positive I have an RVC type though, as the clock only has 3 connectors (two flat pins for ground and +12V, I assume, and one round connector for the coil signal). Am I assuming correctly that if I had an RVI unit and connected it to the car like an RVC unit, with electronic ignition, I wouldn't even have a jumping needle?

I guess I will check the type, all connections and exchange the coil and try again.

[Dan]

I'm afraid it sounds like you have an RVI as the ground is usually through a screw into the instrument case rather than a terminal. Given three terminals, it's probably an RVI. The RVC tachos have one blade and one bullet. Do check though. The change point for the tacho type was the middle of 1976 I seem to remember, if you happen to know what car it came from.

[Gulfclubby]

I'm afraid it sounds like you have an RVI as the ground is usually through a screw into the instrument case rather than a terminal. Given three terminals, it's probably an RVI. The RVC tachos have one blade and one bullet. Do check though. The change point for the tacho type was the middle of 1976 I seem to remember, if you happen to know what car it came from.

I see, the ground is indeed a blade connector, although it is screwed on, too. Might be a later modification. Keeping my fingers crossed. I'm guessing those tachos are no longer available?.

[Gulfclubby]

I'm afraid it sounds like you have an RVI as the ground is usually through a screw into the instrument case rather than a terminal. Given three terminals, it's probably an RVI. The RVC tachos have one blade and one bullet. Do check though. The change point for the tacho type was the middle of 1976 I seem to remember, if you happen to know what car it came from.

I see, the ground is indeed a blade connector, although it is screwed on, too. Might be a later modification. Keeping my fingers crossed. I'm guessing those tachos are no longer available?.

Studied the wiring diagram for a 1275 GT which I guess my tacho is from. Indeed they were fitted with RVI units standard that are hooked up rather complicated with a ground going over the windscreen wiper switch, a feed coming from the coil positive and another one from the +12V terminal of the ignition starter switch. Obviously, I need not even try to set that up properly with the electronic ignition.

So what I need, it seems, is a later model tacho from one of the "normal" minis that came with triple clocks standard, past 1976 which were fitted with an RVC tacho that was grounded over the foil circuit and only had two remaining terminals, a flat one for +12V and a bullet one for the coil negative.

*******, I was really hoping I would never have to take that damn dashboard apart again. I've done it about 20'000 times by now...

[Gulfclubby]

I'm afraid it sounds like you have an RVI as the ground is usually through a screw into the instrument case rather than a terminal. Given three terminals, it's probably an RVI. The RVC tachos have one blade and one bullet. Do check though. The change point for the tacho type was the middle of 1976 I seem to remember, if you happen to know what car it came from.

I see, the ground is indeed a blade connector, although it is screwed on, too. Might be a later modification. Keeping my fingers crossed. I'm guessing those tachos are no longer available?.

Studied the wiring diagram for a 1275 GT which I guess my tacho is from. Indeed they were fitted with RVI units standard that are hooked up rather complicated with a ground going over the windscreen wiper switch, a feed coming from the coil positive and another one from the +12V terminal of the ignition starter switch. Obviously, I need not even try to set that up properly with the electronic ignition.

So what I need, it seems, is a later model tacho from one of the "normal" minis that came with triple clocks standard, past 1976 which were fitted with an RVC tacho that was grounded over the foil circuit and only had two remaining terminals, a flat one for +12V and a bullet one for the coil negative.

*******, I was really hoping I would never have to take that damn dashboard apart again. I've done it about 20'000 times by now...

Ok solution to the problem here:

Turns out the tacho I had was a proper RVC unit from sometime after 1976, was wired correctly and the coil was fine too. However, it was simply broken. I haven't disassembled it yet, but I guess the resistor spring or counterweight or whatever there may be inside is kaputt and that caused it to bounce up and down even when there was no power on it. Exchanged it for an identical unit, same wiring and all that and voila, tacho works just fine now.

Now all I have to get sorted is a slightly leaking tank and the second gear popping out when driving downhill and decelerating. Of course, both of these issues are really annoying too and will be potentially very time consuming to fix... Thanks for everyone's help on the issue solved.