How to Replace Standard Gauges to Rally Gauges

[Jack]

I will try to recreate the write up I did back in 2013

First thing to note is that there are two types of Rally gauges; the early 70s utilize a 12 pin connector, whereas the later years utilize the 16 pin connector with seat belt warning light. The housing is not interchangeable as the connector opening is much larger to accommodate the larger connector. Also note the gauges changed over time (8k vs. 6k tach. Speedo from 160 to 85 MPH, trip odometer, etc.) Most gauges are interchangeable as long as you obtain the correct printed circuit board and realize that some features might not work. For example if you get a 160 MPH speedo it will not have the seat belt warning light, etc.

This write up is for the cluster with 12 pin connector. The volt and fuel gauge wiring is the same for all years (again the face changes some over the years).

In the first post I will cover installing an aftermarket tach. In case someone just wants to install an aftermarket tach.
As most know a tach. needs 3 connections (4 if you have illumination)

Green to negative of coil
Black – ground (-)
Red – ignition (+)
White – dash light (+)

The first connection is the most difficult as you need to pass a wire through the fire wall. But you have two options that does not require going through the fire wall.

Option one uses the battery field wire (brown wire) details to follow.[/li][/list]
Option two use the electronic downshift switch wire (cannot be used with M40 trans)[/li][/list]

Option one uses the alternator field wire
The alternator has three connections, (1) battery (large wire by itself – do not touch); (2) sensing red wire that connects to battery wire – again do not touch (3) field brown wire located next to the red sensing wire that is required to start the alternator and monitor. The brown wire extends all the way to the standard cluster and the dummy battery light. This wire also receives ignition power from the cluster and it is required to be maintained.

Option one step 1 – find alternator brown field wire near master cylinder (main wire harness)
Option one step 2 – expose the same wire and cut it (make sure you expose enough to make two splices)
Option one step 3 – splice the brown wire alternator end (portion that is connected to the alternator) to the ignition power that provides ignition power to the wiper and washer motor also located in the area. You can find the wire as it jumps between the washer and wiper motor (black wire with yellow line). Jump in the car and start it – it should start without any issues BUT your battery dummy light will not come on.
Option one step 4 – crawl under the dash and disconnect the 12 pin cluster connector. Find the brown wire pin #11 and remove or cut that wire. Tape the end that is still connected to the connector (to prevent shorts) and splice a green wire to the brown wire. Make sure that green wire is long enough to reach your tachometer.
Option one step 5 – go back to the cut brown wire under the hood and splice/extend to the (-) of the coil. AND YOU ARE DONE.

Option two uses the downshift switch wire.
Option two step 1 – find the electronic downshift switch wire also near the master cylinder (main harness). The wire is black with orange line.
Option two step 2 – splice and extend the found wire to the (-) of the coil and connect.
Option two step 3 – crawl under the dash and find the downshift connector (connector with 2 wires one orange and the other pink)
Option two step 4 – cut the downshift connector and tape the pink wire to prevent shorting.
Option two step 5 – Use the orange wire to connect the tach green wire (splice green wire long enough to connect to the tach green terminal). AND YOU ARE DONE.

The next few steps are common to both options.

Step 6 – black tach terminal is ground (or earth to some) extend/connect to any metal part – make sure you have good contact.
Step 7 – red ignition (+) terminal, extend a wire to the pink downshift switch or cut wire (depending on option 1 or 2) the pink wire is a fused ignition feed.
Step 8 – white tach dash light, find the nearest dash light (I use the shifter light) and splice into the tan wire.
Step 9 – mount your tach. and enjoy.

SUN SUPER TACH I INSTALLED WITH THE 4 WIRES CIRCLED

[NOT A TA]

Thanks for putting this back up Jack. I used to refer folks from other forums to your previous thread but couldn't after we lost all the old threads. I wish I had the time to recreate some of the tech threads I had about certain subjects that were lost.