Crane XR700 & Tachometer

[scotta]

On my 72 Fairlady the PO had installed a XR700 electronic ignition combined with a Fireball PS200 coil. Works well however the tachometer was not working (it was not wired in). Wanted to share my solution and check if anyone knows if there might be issues with what I have done.

There is a lot of differing advise out there on this. But this is what I believe;

I have a tachometer that uses an induction coil to detect the revs. I think referred to as a 3 wire tach.  I am assuming it works by detecting the current fluctuations every time the coil fires to determine the RPM. 

I figure that the coil and the tacho have to be wired in series. 

First diagram is the original setup without the tacho connected. Second is how I have wired it. I am not using a ballast resistor at is it not needed with this setup. 

 

 

 

[Zed Head]

Have you tried it?  Yes, having the tach in series with the coil sounds right.  The question might whether or not the tach can handle the higher current, since the current was limited by the ballast before.  Call it a "6 volt" tachometer, using a 12 volt coil now.

Crane's instructions are very poor and confusing.  And kind of contradictory.  But it looks like the 700 keeps the ballast.  The 3000 doesn't.

http://www.cranecams.com/uploads/instructions/9000-0700_.pdf

[scotta]

You are right about the advice being confusing and contradictory. 

 I’ve not yet run it for any length of time to see if the coil heats up.

 I can try to add the ballast in between the ignition power and gauge and coil. But that will limit current to coil. 

 

[Captain Obvious]

I do not believe the change in current caused by the inclusion or exclusion of a ballast resistor will cause damage to the tach. The ignition coil side of the (early) tach is simply a piece of wire, and the pickup is clamped around that wire. Unless you try to push so much current through that wire that it burns open (like a fusible link), then the amount of current flowing through it probably doesn't matter much.

Edited May 20, 2018 by Captain Obvious
Added clarification for the early tach

[Zed Head]

That's a great point.  I hadn't thought it out, just posed it as a difference to be considered.  The tach should be fine.  I'd forgotten that the current just passes by the tach, not through it.

As far as the coil, it should be fine also.  It's the XR700 that you need to worry about.  Apparently, from the not so clear instructions, you should have 3 - 4 ohms total resistance on the primary circuit.  And, it's probably best to get it via a low ohm coil and a ballast resistor.  Ballast resistors are odd things that automatically change resistance based on current flow time, resistance rises as they get hot.  So, they have higher resistance when dwell is long, time-wise, like at low RPM, then let more current flow at higher RPM, as dwell time decreases.  Mechanical current limiting.  The old pre-electronic age stuff is pretty fascinating once you figure out what they were doing.

Just an observation.  You could just use a 3 ohm coil and probably be fine.  Make sure that the module doesn't get hot and drive it.

I think that you meant PS20 coil, not 200.  And it is supposed to come with a ballast resistor.  The XR3000 is the one that doesn't need a ballast.

http://www.cranecams.com/416.pdf

[SteveC-VA]

I just got my fuel gauge working now on to my tach. I'm having this issue with the tach on my 260 using the Fireball XR700. I tried the wiring as shown in scotta's pic but didn't have the same color combination wires as he listed. My car wiring is hacked everywhere which makes things more challenging. I tried removing the wire from the ballast to coil and the car wouldn't start so I had to go back to how it was. In the pic I have labeled a few wires, I do have the small black/white, it was cut and taped along with the light blue wire. Looking for suggestions to try to get my tach working.

 

[scotta]

Attached is photos of my final cleaned up wiring. Hope this helps

A couple of points;  there are two types of tachometers out there. Three and four wire, they work differently. 

Mine is a Japanese Fairlady. Some of the wire colors are different to the us cars

 

[Zed Head]

3 hours ago, SteveC-VA said:

I just got my fuel gauge working now on to my tach. I'm having this issue with the tach on my 260 using the Fireball XR700. I tried the wiring as shown in scotta's pic

Looking for suggestions to try to get my tach working.

The 260Z was the first year of electronic ignition so your tach would be the voltage triggered tach, not current triggered.  So scotta's solution won't work for you.

Here is a link to the instructions for the XR700.  Look at page 16.  Your tach should work if the blue wire is connected to the coil negative terminal, and the blue wire is unbroken on the way to the tach.  Looks like yours have been hacked at by the coil. 

Also, make sure that original electronic ignition by the fuse box is disconnected, but the wires aren't cut.  The blue wire branches at the module and one leg goes to the tach.  If somebody cut the wires you might lose that tach leg.

  https://static.summitracing.com/global/images/instructions/xr700%20instructions.pdf

 

 

[Zed Head]

Forgot to say, that's on old tach.  sometimes they just die.  Confirm that the blue wire at the tach is continuous with the coil negative blue wire.

And, a GM HEI module would be more powerful than that XR700.  The XR700 is another primitive points-to-electronic conversion system.  If you still have the 260Z electronic distributor, with electronic pickup coils, for $25 you could have a much better ignition system.

[SteveC-VA]

This post was entered on Wednesday evening but didn't post for some reason:   Thanks Zed, I will need to lower the heater core to get in there, I can see the bottom section of the fuse box but nothing more than that. I will get into it this weekend to make sure the wire is removed as well as check the continuity of the blue wire from the tach to coil.

 

I got into the tach again this morning, this is what I have done so far.  Initially I just connected the blue wire to the - coil on the off chance that the blue wire was removed from the ignition module, no luck, engine would not start. I lowered the heater coil by removing the front bolt and took the TIU out and removed the blue wire pin from the connector and heat shrinked it. I checked continuity from the blue wire under the dash on passenger side to the blue wire terminal near the coil, it checked good. I then dismantled the dash and pulled the tach out and I have 12 volts on the green wire when checked to ground and also checked the green to black and same 12 volts is there. I pulled red wire from the back of the tach post and checked continuity to the terminal on the blue wire near the coil and shows 2.197k ohms, this tells me the wire is good and the 2200 ohm resistor are good. I checked voltage on the red wire with the engine running and see a low, .03 to .06 varying voltage.  From all my checks this leads me to the conclusion that I have a dead tach. Is there a way to test the tach by connecting it to a battery and the coil?

[Zed Head]

2 hours ago, SteveC-VA said:

  Initially I just connected the blue wire to the - coil on the off chance that the blue wire was removed from the ignition module, no luck, engine would not start.

I pulled red wire from the back of the tach post and checked continuity to the terminal on the blue wire near the coil and shows 2.197k ohms, this tells me the wire is good and the 2200 ohm resistor are good. 

If you still have things disconnected, measure continuity from the post on the tach that the red wire was connected to, to ground.   Or measure continuity to ground at the blue wire terminal by the coil, with the red wire connected.  It sounds like your tach might be shorted to ground at the red wire post.  So when you connect the blue wire to the coil it also shorts to ground which would cause the ignition system to malfunction.

There's a guy out there somewhere that rebuilds these tachs.

[SteveC-VA]

I had everything buttoned up when I got this. I pulled the tach out of my other car and hooked it up and it worked sort of, it is erratic and jumps around. In the second video, you can see how bad it is and after I turn th ecar off, the tach reads at various levels, not sure what is happening there.

 

I did test the other tach that I pulled out, the terminal where the red wire attaches to the case of the tach and read around 2.5 M ohms.

 

 

Edit: sorry for the poor video quality.

Edited July 7, 2018 by SteveC-VA