tach swap

[chiquete]

i do a quick search, and no answer... i put a 260z tach in my 74 240z, the problem is that in the rear of the new tach are 3 wires(red, black and green) and i dont know where to connect them, and near the coil are just 2 wires (yellow and green) both are disconnected.

thanks for you commentaries.

[EScanlon]

You need to check the connector for your tach AT the dash harness. If the dash harness has a 4 wire connector with 4 wires: Green; Green/White; Black/White and Black, then you MUST use the 4 wire Tach. The 3 wire Tach is a later model tach and will not work with your dash.

The later model tach used different circuitry for the connection to the coil. Unfortunately, the only diagram that shows that 3-wire tach that I have, shows it to be connected to an 8-wire connector to connect to the wiring harness.

The Yellow and Green wires you mention as being next to the coil don't show up in any of my schematic drawings.

Enrique

[chiquete]

ok thanks, i made the same cuestion in zcar.com, and somebody give me the answer, this is a 260ztach in a 240z dash, so the green is for current, black is ground and the red is for the negative post in the coil (whit a 2200 ohms resistor). i check tomorrow in the morning...

i read your public profile, que tipo de traducciones haces? im from Mexico

[EScanlon]

Traducciones tecnicas, aunque con que me paguen... Tipicamente de Inglés al Español, aunque tambien al revés. Aunque llevo 22+ años aquí, mi familia siempre ha sido bilingue. Yo tambien hablo Frances, y suficiente Portugués para meterme en lios.

Let us know if that wiring set-up works. I haven't heard of anyone being able to get a later tach to work on an earlier dash harness, and it would be great to pin that down for folks here.

Enrique

[chiquete]

I forgot to mention that is a distributor from a 1981 280zx (e1280 Ignition Module)

[V8-240Z]

I found out that there are at least two types of tachs for the 240Z and 260Z-280Z. One type is a four wire positive trigger tach used on the 240Z and the other is a three wire negative trip tach.

The 4 wire type in the 240Z has one wire that sends positive voltage to the tach, one wire is for ground and the other two leads are the trigger loop, one coming and the other going. From past experience I have found that this type of tach is very unreliable.

The 3 wire type of tach is more reliable and more adaptive to aftermarket modifications to the ignition system. The 3 wire type has a positive lead, a ground and a negative trip lead that runs directly from the male bullet post on the back of the tach to the negative terminal on the coil. Looks like ZX ignition may need 2.2K resistor inline from the bullet post that goes direct to the "-" post on the coil. The ZX tach resistor is 2.2K ohms, 1 watt, and part number 7321-9300. You will know the resistor is needed if the tach jumps all over.

OK, here is what I have done with my 240Z. I removed my old 4 wire tach and replaced it with the three wire. Put the new 260Z-280Z tach guts in the 240Z metal housing, and swap the faceplates to keep the redline accurate. The needle pops off, don't damage it. One important detail in the wiring. The ground wire and the power wire are reversed between the 240Z tach and the 260Z-280Z tach. Connect the 260Z-280Z tach's sensor lug back to the negative terminal on the coil. This is the male bullet post on the back of the tach. This will take a wire you will need to add, 16-18ga will be just fine.

My 240Z is a V8 but the swap is the same for the L6 the only thing I did different was to turn the calibration screw on the back of the tach so it would read correctly for a V8.

NOTE: Make sure you reverse the power leads on the back of the tach, compare them before you swap you will notice the + and - are reversed. The little "loop" from the 240Z tach is a + pulse trigger and is simply left alone with this swap. Just push it aside. If you cut it the car won't start. (Don't ask)

[RacerChuck]

I'm trying to help a friend who has a 260Z with a 4 Wire Tach. We have converted the engine over to a Malorry Unilite Distributpr and Coil Setup.

I understand that the black wire is the ground and another is probably the backlight illumination.

When you mention "Trigger Loop" do you mean that the two remaining wires connect (1) to the positive Side of the Coil and the other (1) to the Negative?

If I know the Black wire is a ground, I can just keep touching the remaining three to the posive side of the battery until I see the Backlight Light Up - that will mean that the two remaining are the Trigger Loop Wires. then within a maximum of two try's I will have the distributor working

Am I on the right track?