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 3 hours ago3 hr by inline6

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