18 replies to this topic

[unique_name]

One thing I forgot to ask is what gauge wiring should I use to connect from the rev counter to coil?

 

Ohh and my address is;

 

Name: Bruce Wayne

Title: Not Batman
Company: Dark Knight Inc.

[unique_name]

  The crimp tag on the end of your red main battery cable is very poorly made, I imagine that it will show fairly high resistance and when it comes to delivering 150 amps will be a hot spot.  Someone has tried to get away without having to buy the proper, £75.00, heavy terminal crimp tool.  Doesn't work, you need a lot of force to close these crimps.  I am also concerned, as above, about why you are asking about a positive and negative at the solenoid.  The solenoid negative is it's mounting bracket, all the cables on it of whatever size are positive.

 

  Judging by the presence of a positive supply to the dizzy in your diagram I imagine you have electronic ignition.  This is an RVI tacho and simply put, will not work with your ignition if it is electronic.  In case that's an error on the diagram however:

 

  1 is tacho ground (actually I think they have used the wrong screw, it should be the small one by the bullets.  The one they have used is for something internal that hopefully hasn't been messed up by removing the screw), 4 is tacho power.  These do not have to go anywhere near the coil, they are just the power supply to the instrument. As standard tacho power would come from the accessory circuit (stereo, heater, wipers etc.), and the ground would be provided through the instrument PCB so this was originally a 2 clock car I would imagine.  Without swapping to the correct 3 clock PCB, which would provide that ground, you are going to have a hard time providing illumination to this gauge too.

 

  2 and 3 are the sensing circuit for the gauge.  The ignition supply cable (white) must run from the ignition switch to 2, then another cable from 3 to the coil provides coil power (white/green).  It's an RVI.  In order to provide immobilisation the white cable must also run through your alarm.  Without knowing more about the alarm it's hard to say for sure but judging by the diagram you have provided I would run it from the ignition switch, to 4 on the alarm, then from 3 on the alarm to 2 on the tacho, then from 3 on the tacho to + on the coil.  All other wires you have on the diagram are not needed.  There are too many white/red wires here and the extra white cable you can't trace must be the ignition supply I imagine.

 

  The diagram for this clock would be that of a 1975 1275GT.  Who knows what diagram the rest of the cars needs though!

 

Hi All.
 

So I have tried Dan recommendations above and I have had no luck. These are the combinations I have tried. The numbers refer to my original diagram in my first post.

 

Ignition Supply - #2 => #3 to Coil. RV counter doesn't work and car doesn't work. 

Ignition Supply - #3 => #2 to Coil. Same result as above.

 

Ignition Supply - #3 => #4 to Coil. RV counter doesn't work, Car starts

Ignition Supply - #4 => #3 to Coil. Same result as above.

 

So I was only testing the sensing circuit of the tacho. Does the Tacho ground  #1 and #4 Tacho power need to be connected for the sensing circuit to work?

 

Any other suggestions would be great.. Thanks All

[unique_name]

Any advice?

[dklawson]

Dan has identified the tach as the RVI type.  You said it worked before so it should work now as long as you have not changed from points to electronic ignition.  However, RVI tachs are NOT a modern type tach and they are not wired like most people think.

 

RVI tachs are current pulse sensing and are sometimes referred to as "impulse tachs".  Dan pointed out the two bullet connectors on the back of the tach.  I believe he also pointed out a couple of other connections.  I will elaborate a bit on his earlier information.

 

The spade lug next to the bullet connectors needs a switched, fused 12V supply.

Though seemingly wrong, provide an earth connection using a ring terminal on the end of an earth/ground wire connected under the head of one of the screws with the rubber insulators.  Those screws will be in contact with the metal frame inside the gauge.

The two bullet connectors are connected in series with power going to the coil and I will elaborate below.  You have two possibilities for how to utilize the bullet connectors.  I will provide both explanations since I don't know what your preference is and/or what wiring you currently have.

 

The following is an either/or choice.  Select the wiring method that is easier/better for you.  You do not use both wiring schemes at the same time.

 

Car Interior Bullet Wiring:

Locate the white wire leaving the ignition switch and going to the coil (+) terminal.  

Disconnect that wire and extend it so you can connect it to one of the tach bullet connectors.

Make a second white wire and run it from the now empty ignition switch terminal to the remaining bullet connector on the tach.

Start the engine.  If the tach works as expected, great.  If not, swap the two white wires on the back of the tach.  (Yes, you will have to change the wires' bullet connector gender to do that).

 

Engine Bay Bullet Wiring.

If you do not want to mess with the ignition switch wiring as described above, your only other choice is to make changes to the coil wiring in the engine bay as follows. 

Run two new white wires from the back of the tach to the engine bay.  The wires must reach the coil.

Disconnect the white wire coming from the ignition switch that is connected to coil (+).

Splice this wire to one of your two new white wires connected to the tach.  

Connect the remaining wire coming from the tach to coil (+).

Start the engine.  If the tach works as expected, great.  If not, swap the two white wires at the coil.  

 

Why is it so complicated?  It's not really.  What you are doing with either of the wiring schemes above is passing the coil current THROUGH the tachometer.  Inside the tach is basically a pulse transformer.  Each time the coil charges and discharges a small pulse is created inside the gauge and those secondary pulses are then used by the circuit that moves the needle.  

 

Modern tachs and the later Smiths RVC tachs are simpler to wire.  They use a single sense wire connection to coil (-) to determine when the coil fires and in effect... directly count the voltage pulses.

 

As Dan said, RVI tachs do not like electronic ignitions.  If your RVI tach does not work properly after swapping white wires around, give up and buy a modern or Smiths RVC tach.