Tachometer

[daddydonuts]

I have a stock 73 240 z Tachometer, I changed the points distributor to a pertronix electronic ignition and flame thrower coil. My tachometer does not work now, I know there is an easy fix but I am electrically challenged, any advice would be appreciated.

[Six_Shooter]

Easiest way to get the tach to work is to get a late 280Z tach, they were points triggered tachs.

[RTz]

The 240 tach is triggered off the positive terminal of the coil. Did you happen to change that with your mods?

[daddydonuts]

The 240 tach is triggered off the positive terminal of the coil. Did you happen to change that with your mods?

 

That is it then, the stock wires are not used with the pertronix upgrade. Thanks

[rejracer]

I used the stock wires when i did the 280zx distributor upgrade. To get my tach to work I had to get a 280z tach and swap out the guts and I think I even had to break the link between the GW wire (tach signal) and start/crank voltage. It's been 15 years since I've done it, so I can't remember if I did that part of it or not.

[daddydonuts]

I have done searches and read threads from HZ with no luck. I even bought a 280z tach and no luck

This may be in-experience talking, but using the pertronix with the stock 40amp alternator and voltage regulator and having my pertronix upgrade wired correctly according to a post on HZ may cause the problem with my tach not getting a signal from the coil?

[beermanpete]

The 73 tach is the 4-wire type. The tach senses the ignition current pulses in the positive side of the primary circuit. Unless you significantly rewired the ignition and tach cicuit, you need to use the 3 original wires on the positive side of the coil. There are 2 black/white wires and a green/white wire. If you reverse the 2 black/white wires the car will run but the tach won't work.

 

To identify which black/white wire is which:

 

1) Remove all 3 wires from any terminal at the coil and ballast resistor.

2) Test for voltage at each wire with the key in the ON and CRANK positions.

3) One black/white wire will have +12V when the key is in the ON and CRANK positions. Connect this wire to one end of the ballast resistor.

4) The other black/white wire will only have voltage in the CRANK position. Connect this wire to the positive side of the coil.

5) Connect the green/white wire to the other terminal on the ballast resistor.

6) Connect the red wire from the Pertonix to the black/white wire on the ballast resistor.

 

If you are not using the ballast resistor, connect the black/white wire identified in step 3 to the green/white wire.

[daddydonuts]

The 73 tach is the 4-wire type. The tach senses the ignition current pulses in the positive side of the primary circuit. Unless you significantly rewired the ignition and tach cicuit, you need to use the 3 original wires on the positive side of the coil. There are 2 black/white wires and a green/white wire. If you reverse the 2 black/white wires the car will run but the tach won't work.

 

To identify which black/white wire is which:

 

1) Remove all 3 wires from any terminal at the coil and ballast resistor.

2) Test for voltage at each wire with the key in the ON and CRANK positions.

3) One black/white wire will have +12V when the key is in the ON and CRANK positions. Connect this wire to one end of the ballast resistor.

4) The other black/white wire will only have voltage in the CRANK position. Connect this wire to the positive side of the coil.

5) Connect the green/white wire to the other terminal on the ballast resistor.

6) Connect the red wire from the Pertonix to the black/white wire on the ballast resistor.

 

If you are not using the ballast resistor, connect the black/white wire identified in step 3 to the green/white wire.

 

I will try that tonight, Thanks!

[daddydonuts]

I will try that tonight, Thanks!

 

So 40 years of being wired incorrectly...I removed some wires from the stock harness that runs in from the front of the car (it was spliced up), I have the following color wires that should be original: Black wire, Black w/yellow stripe, Green w/white stripe, Black w/white stripe, Green, and Yellow w/white stripe. I know the YW wire is for the temp gauge sensor, the BW wire goes to the ballast resistor (along with Red pertronix wire): no clue what the green wire is for and the BY wire either. The engine will run with the BW wire (pertronix red) connected to the ballast and the green wire hooked to the + side of the coil. GW wire hooked up to the other post on the ballast still does not send a signal to my tachometer. The BW and green wire both have voltage in the key on position and when starting. BW-11.3 & 10.03, green-11.15 & 9.7 when key on and start respectively. Any suggestions?

[beermanpete]

One of the black/white wires comes from the ignition switch to power the ignition system. This is the one that should be +12V with the key in both the ON and START positions.

 

The green/white wire goes from the ballast to the tach AND to the ignition switch. In the START position it gets connected to the +12V circuit, effectively shorting out the ballast. This helps the car start easier by providing a hotter spark.

 

The other black/white wire comes from the tach to the coil + terminal.

 

The black wire should go from the coil - terminal to the distributor. Since you have the Pertronix system installed this wire may have been removed.

 

The manual shows a black/yellow wire for the throttle opener solenoid. Perhaps they have been mixed up?

 

It is possible the color codes in the manual do not match the car due ot a mistake in the manual or a producution change in the cars.

[daddydonuts]

One of the black/white wires comes from the ignition switch to power the ignition system. This is the one that should be +12V with the key in both the ON and START positions.

 

The green/white wire goes from the ballast to the tach AND to the ignition switch. In the START position it gets connected to the +12V circuit, effectively shorting out the ballast. This helps the car start easier by providing a hotter spark.

 

The other black/white wire comes from the tach to the coil + terminal.

 

The black wire should go from the coil - terminal to the distributor. Since you have the Pertronix system installed this wire may have been removed.

 

The manual shows a black/yellow wire for the throttle opener solenoid. Perhaps they have been mixed up?

 

It is possible the color codes in the manual do not match the car due ot a mistake in the manual or a producution change in the cars.

 

Ok, looked in my clymer manual and the BY wire is for the solenoid that used to be on the intake (removed now). According to my manual the green wire is for the horn or fuel pump, that is incorrect. I only have one BW wire in my harness, and it goes to my ballast along with my red pertronix wire. Now I'm left with a green and BW wire that are hot at on and start, and a black wire that I will be investigating. Are the hot wires supposed to have any spliced wires?

Edited August 5, 2012 by daddydonuts

[beermanpete]

I never saw any splices in the wiring on my '73.

 

Are you disconnecting all the wires while you test to see when the voltage is present at each? If you test it with the wiring connected to the ballast and coil you will get misleading results.

 

Is you car running now? Does the tach work?

[daddydonuts]

I tested the six wires from my harness, un-connected, I can make the car run with the single BW wire and the green wire only. Nothing to my tach though.

Edited August 6, 2012 by daddydonuts

[NewZed]

The 73 FSM page BE-5 has a legible wiring diagram if you want one more to look at. Shows power to the coil (+) terminal as - Ignition switch > GW wire > Tach > BW wire > Coil (+) terminal

 

So if you don't have power running through the tach on (GW in) and (BW out) you won't get any needle movement. Assuming the FSM represents what you have and is not in error.

 

 

www.xenons30.com/reference

[beermanpete]

I tested the six wires from my harness, un-connected, I can make the car run with the single BW wire and the green wire only. Nothing to my tach though.

 

You should look at the wires at the tach and the ignition switch. It sounds like the wiring has been worked on in the past. Maybe someone made a mistake repairing it or cross-connected something.

[daddydonuts]

I'm really apreciating all the advice and I am trying each of your suggestions. I think I am gonna have to trace the wires from the tach forward

[daddydonuts]

The 73 FSM page BE-5 has a legible wiring diagram if you want one more to look at. Shows power to the coil (+) terminal as - Ignition switch > GW wire > Tach > BW wire > Coil (+) terminal

 

So if you don't have power running through the tach on (GW in) and (BW out) you won't get any needle movement. Assuming the FSM represents what you have and is not in error.

 

 

www.xenons30.com/reference

 

After looking at the FSM wiring and reading the above post about the 4 wire tach harness in the dash, mine only has three wires, GW, and 2 black. The wiring diagram in the FSM has all 4 colors:GW, BW, Green and black, and I have all 4 colors at my harness at my coil. I have power to the GW and middle black wire on my dash harness. Any way to test the tach to see if it works. I also have a 280z tach that I can switch out with the 240z tach, neither get a signal from my dash harness.

[daddydonuts]

Dash harness

 

 

 

Gauge

[beermanpete]

You have a 3-wire tach. What year is your car? I am under the impression that the early cars (with points) came with the 4-wire tach. Perhaps someone has modified your car to use the later tach (or some early models came with the 3-wire tach). Either way, the wiring diamgrams I have for the 72 and 73 do not apply.

 

The 3-wire tach senses the engine speed on the negative side of the coil. The single yellow wire on the tach should be sensing wire and goes to the negative side of the coil. The other 2 wires are +12 (yellow/red) and ground (black). You should be able to trace the sense wire from the tach down to the igniton harness near the coil with an ohmmeter or buzz box. The power and ground wires most likely do not go into the engine compartment. Verify that power is present with the key on and the ground is solid.

[daddydonuts]

You have a 3-wire tach. What year is your car? I am under the impression that the early cars (with points) came with the 4-wire tach. Perhaps someone has modified your car to use the later tach (or some early models came with the 3-wire tach). Either way, the wiring diamgrams I have for the 72 and 73 do not apply.

 

The 3-wire tach senses the engine speed on the negative side of the coil. The single yellow wire on the tach should be sensing wire and goes to the negative side of the coil. The other 2 wires are +12 (yellow/red) and ground (black). You should be able to trace the sense wire from the tach down to the igniton harness near the coil with an ohmmeter or buzz box. The power and ground wires most likely do not go into the engine compartment. Verify that power is present with the key on and the ground is solid.

 

My car is a 8/73 240Z, I will try that tonight, betting that the tach was replaced over the years...thanks.

Edited August 8, 2012 by daddydonuts