I am working on installing a set of Speed Hut gauges in my 240z (my "track car"). Manufactured in 12/70, the wiring for the tach doesn't match the wiring diagrams I see online. Other than power and ground and illumination wires, the Speed Hut tachometer has a single yellow wire that is supposed to be hooked up to the "coil -".

It seems to me, after looking at the stock wiring, I have to not only figure out which wire is "coil -", but I think I may have to connect some of the other stock wires together in order to "bypass" the stock tach.

Color legend is:
blue = L
yellow = Y
Black = B
Red = R
White = W
Green = G

Ignoring the wires for gauge illumination, I am looking specifically at a 4 prong connector for the stock tach. Here is what I am looking at... on the left are four wires from the harness that are in the 4 prong connector, and on the right are the four wires coming from the tach that are in the 4 prong connector:

Harness wiring	Description	Connection	Tachometer wiring	Description
RL	red with blue stripe	----	YR	yellow with red stripe
GW	green with white stripe	----	W	white (with black band on it)
B	black	----	B	black
BW	black with white stripe	----	W	white (with red band on it)

Additionally, I am running a Crane HI6 (multiple spark discharge) ignition which also has tachometer adapter hooked into the circuit. The ignition and adapter were previously in use and worked perfectly with the stock tach. The wiring for the ignition and adapter has been untouched since the car ran.

What I need help with:

1. Which wire is the negative from the coil?

2. Which, if any, wires do I have to jumper together with the stock tachometer no longer in place?

My guesses are:

1. Black - connect the Speed Hut yellow wire to the black wire in the 4 prong connector

2. Connect (jump) the green with white stripe wire and the black with white strip wire (to bypass the stock tachometer)

But, I am not sure. And don't know what to do with the last of the four wires (red with blue stripe at the four prong connector).

Edited 13 hours ago13 hr by inline6

Give me a call

15 hours ago, inline6 said:

I am working on installing a set of Speed Hut gauges in my 240z (my "track car"). Manufactured in 12/70, the wiring for the tach doesn't match the wiring diagrams I see online. Other than power and ground and illumination wires, the Speed Hut tachometer has a single yellow wire that is supposed to be hooked up to the "coil -".

It seems to me, after looking at the stock wiring, I have to not only figure out which wire is "coil -", but I think I may have to connect some of the other stock wires together in order to "bypass" the stock tach.
...
Ignoring the wires for gauge illumination, I am looking specifically at a 4 prong connector for the stock tach. Here is what I am looking at... on the left are four wires from the harness that are in the 4 prong connector, and on the right are the four wires coming from the tach that are in the 4 prong connector:

Harness wiring	Description	Connection	Tachometer wiring	Description
RL	red with blue stripe	----	YR	yellow with red stripe
GW	green with white stripe	----	W	white (with black band on it)
B	black	----	B	black
BW	black with white stripe	----	W	white (with red band on it)

Additionally, I am running a Crane HI6 (multiple spark discharge) ignition which also has tachometer adapter hooked into the circuit. The ignition and adapter were previously in use and worked perfectly with the stock tach. The wiring for the ignition and adapter has been untouched since the car ran.

What I need help with:

1. Which wire is the negative from the coil?

2. Which, if any, wires do I have to jumper together with the stock tachometer no longer in place?

My guesses are:

1. Black - connect the Speed Hut yellow wire to the black wire in the 4 prong connector

2. Connect (jump) the green with white stripe wire and the black with white strip wire (to bypass the stock tachometer)

But, I am not sure. And don't know what to do with the last of the four wires (red with blue stripe at the four prong connector

(this is for anyone else interested in a little information about some specifics that you raise:)

1. NONE of the above are "Coil - ". (Stock config = Coil "-" is connected to the points output of the distributor. So, new wire from the Coil "-" to your new gauge...(it will be a 2nd wire connection as the Coil "-" needs a "signal to fire" from points or an electronic ignition unit as well - your new gauge is just tapping into that signal))

2. You don't necessarily need to jumper any of the wires in that connector, but you need to understand the coil wiring to decide whether to JUMP or just ABANDON the G/W and B/W in the connector pictured above. The stock circuit goes like this: IGN SWITCH -> B/W -> Ballast Resistor -> G/W -> Tach connector -> Loop on back of Tach -> Tach connector -> B/W -> Coil "+". The coil gets power at IGN ON through this and the Tach "senses" the flow of electricity to the coil. If you're replacing the stock Tach, the re-route of the B/W back to the Tach is not necessary - the B/W and G/W to that connector can simply be ignored (abandoned). SO - the B/W that goes to the Ballast can be connected to the Coil "+" - either through the Ballast (by removing the G/W and running a short wire from there to the Coil "+") OR bypassing the Ballast and connecting the "ballast's" B/W directly to the Coil "+" instead - IF you no longer need a Ballast Resistor in the circuit.

note: I think it's better to abandon and get all that extra wire (and added resistance) OUT of the power circuit to the coil...

BTW, the other two wires in that connector: Black - is a Battery Ground. R/L is gauge lighting - it's listed in the wiring schematic as "IL". So Black is the power ground for the Tach - the Tach gets power (battery voltage) from a Green in another connector.

Edited 12 hours ago12 hr by cgsheen1