Electrical Systems Last Update: May 4, 2009 11:01 PM

Digital Speedo:

The NA (1990-97 model years) Miatae have a cable driven speed but the LS1's T56 Transmission like all new cars have digital speedometers. There are a couple options to get the stock gauge working but I decided to use an aftermarket digital gauge and install it inside the miata gauge cluster. I bought the gauge from Jeg's, its a Cyberdyne C270E351N and cost $130. I chose it because it has a built in shift light and other neat features like 0-60, 1/4 mile, max speed and other functions. It is also cheaper than most of the other methods. Below are the physical modification I made to get it to fit in the Miata cluster.

I am going to quote Steve from this miata.net forum thread below because he does a good job explaining the install:

This speedo does not drop in. It must be disasembled and the plastic case modified, probably voiding the speedo warranty. The miata cluster is not modified and the stock miata speedo can be reinstalled later if desired.

The guage is delicate and ESD sensitive. Since the guage is designed to replace aftermarket cable driven speedos, the case is mostly hollow.

The speedo is held together by the bezel, which clamps the lense, face, and circuit card to the lip of the case by crimping the bezels edge. A small flat blade screwdriver is used to pry the crimping away from the case. The bezel is not going to be used so it can be cut off.

With the bezel off, the thick colored lense slips off. The face is staked in three spots around the guage to the lip of the case with gentle prying.

The circuit card is a snug fit into the counterbore of the plastic case. Cutting the back end of the case off makes gentle pressing around the circuit card from the inside easier. Don't get in a hurry. A plastic screwdriver handle works well. Only hold the card by the edges or wires. For those with no respect for ESD, it may be better to leave the card in so it will not be handled and trim the plastic case with a hand-held hacksaw blade, being careful not the cut the soldered-on wires. The case should measure 2 inches from the front of the lense to the case cut, bezel off. This is the thickness of the miata oem speedo. The circuit card will be atleast 3/4 inch away from the cut.

The miata cluster has a step in the case at the bottom. The speedo case must be trimmed to clear this step, allowing the speedo case to sit flat inside the cluster case.

There is a push button momentary switch on the guage face. Pushing this button recalls 0-60 times, highest rpm achieved, 1/4 mile times, calibrates the shift light, sets the trip meter, adjusts the tach for the number of cylinders, and calbrates the speedometer. A small hole in the cluster lense is required to either use a pen or paper clip to press the button or glue a extension to the button so it will protrude from the cluster lense like the oem trip meter button.

The odometer is not adjustable and can go to 999,999 miles.
The trip meter goes to 999.9 miles.
The tach will register to and the shift light is adjustable up to 9900 rpm.
The tach calibrates to 2, 4, 6, or 8 cylinders.
The speedo calibrates to any speed between 1000 and 200,000 pulses per mile.

The unit is setup to dim whenever the cluster lights are on. 5 wire hookup, pos, neg, tach sig, dimmer, and speed sensor. Only the speed sensor wire must be run through the car. Everything else is available at the cluster.

Note that in the first five pictures below, the blue transparent Cyberdyne gauge face and bezel is off.

Below is the step that the speedo housing has to clear.

Now the blue gauge face is back on.

It makes a tight seal with the stock cluster face.

The first sign of life... I'm getting excited.

Installing the PCM:

I, like most people, use the factory GM PCM because it is highly capable and can be reflashed with nearly and calibration and settings. No need for aftermarket hardware, just software.

This is the factory mouting clip for the PCM, I modified it to fit in to the Miata.

Yes, I zip tied it to the Miata fuse block. It was easy and quick. I will probably come up with a better mounting solution in the future but this will surely work for now. You can also see the five pink and two orange wires I had to take from the LS1 harness and connect to the miata harness. These are not the only wires that have to be connected though. There are some others like starter, alternator, and gauges.

It is a very tight squeeze between the firewall and shock tower. A little firewall "massaging" would help but I didn't want to hammer my new paint...

Wiring Harness Modifications:

Here are the full instructions:

You can download a .rar of the wiring instructions here: Right Click Save AS

  1. Make sure the grounds from LS1 engine wiring harness are bolted on the back of the driver side head.
  2. Make a ground strap from the engine block to chassis; recommend a 4-6 gauge wire. There are available bolt holes on the passenger side of the block near the coolant ports for the heater.
  3. Locate the main chassis wiring harness on the Miata.  This is the harness that runs along the powerplant from the factory. In the main wiring harness is a main power wire and it runs directly to the starter. There is no modification required to hook this wire up to the LS1 starter.
  4. Also in the main chassis wiring harness is a small black/red wire. This wire also connects to the starter. This wire is the trigger wire for the starter. Cut the factory Miata spade terminal off the wire and connect an eyelet terminal. You can use the eyelet off the LS1 harness as you will not be using that wire. Once the correct terminal is attached, bolt the wire to the LS1 starter.
  5. Locate the factory Miata alternator wiring. You will need to lengthen the larger alternator power wire to reach the LS1 alternator (length will depend on how you want to route the wire). Make sure to use thick wire as it carries a heavy electrical load.
  6. Along with the large alternator wire, there is a white/black wire from the Miata alternator connector. You will need to lengthen this wire to the LS1 alternator. There is a red wire on the LS1 alternator connector, splice the white/black wire into this wire. The rest of the red wire on the LS1 wiring harness will not be used. Be sure to properly tape or remove the wire. Note that there is a white/green wire from the Miata alternator connector that is currently unused. You will use this wire in step 8.
  7. The LS1 wiring harness has 5 main connectors besides the 2 PCM connectors. 3 big connectors and 2 small connectors.  Locate the 3 big connectors and cut the 5 pink wires (note: one of the wires might be pink/black).  These wires need to go to a 12V switched source that is fused (only gets power when in the run and start positions). We recommend using white/red wire that can be found under the hood of the Miata on an 8-pin gray connector. This wire is a fused 30amp circuit that previously powered the Miata engine.  See picture “A” and “B”.
  8. There are 2 orange wires on the 3 big connectors. These wires need to go to a 12v constant circuit. You can hook these wires up the white/green wire that was left over from the Miata alternator.
  9. Locate the gray 10 pin connector on the LS1 wiring harness. This connector has a dark green with white stripe wire. This wire is the fuel pump power wire. You will need to connect this wire to a fuel pump relay. It is possible to use the factory Miata fuel pump relay but you will have to rewire it (the LS1 sends out a 12v signal and the Miata sends out a ground signal). The Miata fuel pump relay is located under the steering column and is a yellow connector with 4 wires(OR 5 wires if you have 1.6L car, see Fuel Pump Relay below); 2 white/red power wires, blue/red wire that runs to the fuel pump and the light green trigger wire that turns the relay on. To modify the Miata relay, cut the white/red that is located directly next to the blue/red wire and ground the white/red wire. Make sure you cut it long enough to extend to a potential grounding location. See picture “C” and “D”. Now you have to connect the dark green with white stripe wire to the light green trigger wire.  You can do this in 2 different places; the stock Miata data link connector under the hood or the wire coming from the Miata PCM. The data link connector is the easiest because there is only one light green wire in there. If you opt to connect it to the PCM wiring, you will have to locate the Miata PCM extension harness under the dash, behind the glove box.  The PCM extension harness has 3 connectors: a 26 pin male connector, a 22 pin male connector, and a female connector. Locate the 22 pin male connector and you will see the light green trigger wire.  See picture "E".
  10. Find the black 8 pin connector on the LS1 harness. There is white wire located a pin “G”. This wire is your tachometer signal. The LS1 tachometer is a 4 cylinder signal so you do not have to modify your tachometer for it to work properly. On the passenger side, behind the glove box is connector in the very top right corner (it is very high up in the dash). There is a black/white wire located in the connector.  Make sure the connector stays connected but splice the white wire from the LS1 harness to this black/white wire. Make sure you connect the wire to the wiring that runs towards the gauge cluster. See picture “F”.
  11. Now move to the small LS1 harness connectors. On the blue 10 pin connector, locate the brown/white wire, pin “B”. This wire is used for your MIL light. This wire needs to be connected to a yellow/black wire that runs to the cluster. Like the fuel pump relay, you can do this in 2 locations. The first is the data link port under the hood. The second option is using the same connector the tachometer wire was spliced into. See picture “F”.
  12. Find the brown 2 wire connector on the passenger side of the transmission. Cut the connector off and make sure you leave enough wire on the connector to splice it into the Miata harness. There are 2 single wires that are located in the main Miata harness that we addressed first. The wires are red/green and black/yellow. Connect these wires to the “cut-off” connector and hook it back up to the transmission. You now have back-up lights.
  13. Locate the section of the harness that attached to the Miata engine. There is a yellow/red wire with a spade connector that connected to the Miata oil pressure sensor.  The LS1 sensor can not be adapted so use the supplied adapter nut to install the Miata oil pressure sensor into the LS1 block.
  14. Also in the engine bay is a yellow/red wire that ran to the Miata coolant temp sensor. This wire changes to black/blue at the cluster. Use the supplied adapter to install a Miata coolant temperature sensor into the LS1 block.  See picture “A” and “B”.
  15. Depending on the year of your chassis, you may need to locate and OBD2 port. The connector will  gets one power, 2 grounds, and a dark green wire from the LS1 computer. The dark green wire is located on the blue 10 pin connector, pin "K". See the attached diagram.

GM OBD2 Connector Pinout

Here you can see where I chose to ground the engine block. I actually reused the ground cable (with connectors still attached) from the LS1 wiring harness.

You have to lengthen the alternator wiring since the LS1 has it on the passenger side and the Miata has it on the driver side. I ran my wiring along the top of the k-member as seen. The alternator is in the top right.

This is why I hate wiring, it always looks like a rats nest. I ran the LS1's wiring that goes inside the camaro inside my miata in the driver side firewall area. This harness has things like tach, OBD-II data, speedo, etc.

This is it coming in where the old speedo cable came in, right above the throttle pedal.

I even used the Miata speedo cable grommet for the harness...aren't I clever. I thought so.

The above picture is of the underside of the trans tunnel. That is the factory Miata battery cable harness that normally runs along the PPF but I have relocated to the top of the tunnel. The two connectors seen are for the reverse lights. To get them to work with the T-56, simply cut off the T-56 connector (with plenty of wire on the connector so it can reach said Miata connectors) then splice them into the Miata ones. Since its a switch, it doesn't matter which wires you pair up, just pick one.

Sorry for the blurry pic. This the the T-56 connector and about one foot of its wiring spliced into the factor Miata reverse light harness.


Fuel Pump Relay:

This the the fuel pump relay connector located under the steering column (called Circuit Opening Relay in wiring diagrams). On the 1.6l cars its has 5 wires (like mine did) and on the 1.8l cars it has 4 wires and a different relay. I will only discuss the 5 wire relay. The violet trigger wire which comes from the ST Sign fuse (main fuse box in the engine bay) is what trips the relay and sends power to the fuel pump when the violet is 12v. The light green (already removed from the connector in the picture) is not needed as it is an extra fail safe circuit that was connected to the AFM to allow fuel only when the engine was running. Mazda got rid of this for the 1.8l. All I did was hook up the dark green/white fuel pump trigger wire from the LS1 PCM to the purple wire on the connector. Everything else (besides removing the light green wire) remains the same.


DIY Immobiliser and Ipod Hookup:

I followed AutoSpeed's The World's Best DIY Immobiliser article to hook up my own immobiliser that interupts the fuel pump's power supply. My local radio shack had most of the parts needed. I already had a broken key fob that I was able to superglue a special magnetic in. I got a GE window alarm kit that I disassembled to get the magnetic reed switch and magnetic (could not find a magnetic reed switch anywhere in town and didn't feel like waiting for one shipped. The window alarm was only $5 at Kmart.

GE window alarm

Above is what the window alarm looks like.

These are the parts I used with the exception of the "4-N-1" switch, I opted for the toggle instead.

Above is the internals of the window alarm. This is after I de-soldered the magnetic reed switch (at bottom of picture).

I bench tested the setup to insure I had everything wired up correctly.

When activated, the engine will crank and stumble for a few seconds before stalling. I will not disclose where the magnetic reed switch is hidden but here is where I located the LED and arming switch (Autospeed suggest a momentary button but I went with a toggle).

While I was at Radio Shack, I grabbed a 3ft Y-cable to hook into my head-unit and route under the center console and into my armrest (through a drilled hole). My ipod plugs in and stays put even during heavy g's