Pictures of Greg and my gauge clusters.
Greg (auto cluster)
 Greg (auto cluster)
 Gary (manual cluster)
 Gary (manual cluster)
The odometer:
In doing the conversion we had to determine what, if anything, was different between the odometers. The first thing I did was to see if the odometer motors were different. The JDM odometer had security screws which held it in place. Once I broke them free by grabbing them with a pair of wire cutters I was able to finish taking them out using a pair of needle nose pliers. I replaced them with screws that had the same thread and length.
To find if there was a difference in the odometer motors I test the original JDM odometer with a signal driver for a period of one minute at 60 mph. The result was the odometer advanced 1.6 kilomters. Next I swapped the JDM motor with a USDM motor and performed the same test. The result was the same. Although the color of the motor wires may be different the motor and worm gear are the same. I then inspected the odometer gears. After close inspection I found that the JDM odometer had a smaller gear ratio. So the final determination was that only the gear ratio of the odometers made a difference in whether it tracks in kilometer or miles per hour.
 
The fuel gauge light ring:
The fuel gauge light ring has a couple of differences. The most noticable is the color. The color of the JDM ring is red'ish in color with a black band on part of it. The band is to help shield the light given off by the low fuel lamp so it doesn't interfere with the other gauges. The JDM ring also has an alignment notch because of the black band having to face a certain direction. The USDM ring is all blue in color so it doesn't matter how it's installed. Like the backing of the USDM gauge faces, the color of the USDM ring is blue to help aquire a more white color by filtering the OEM incandescent lamps. Incandescent lamps tend to give off a yellow'ish color. Although most USDM gauge clusters I've seen only have a blue ring, some of them will also have a chrome metal split tube to help amplify the light from the lamp. It can be seen in the picture with the blue ring.
The black indicator plate:
Below is a picture of Greg's JDM plate. Notice the indicators for power and hold. Greg's gauge cluster is for an automatic transmission and these indicators coincide with the power/hold switch found next to the shifter. Greg can tell you more about what those functions are for.
Gauge cluster lamps:
The main large gauge illumination lamps in a JDM gauge cluster have white colored filter covers over them as apposed to the the USDM gauge clusters which have blue colored filter covers. This is to help maintain the red color of the gauge as the filtering on the back of the 1999 JDM gauge faces are red'ish in color instead of blue.
Date identification:
The date stamps on the gauge clusters were a little confusing. Greg's cluster has a date stamp of 10.9.30. My 1999 cluster has a date stamp of 11.6.15. Being that these were Yazaki Meter gauge clusters I knew that the year was the first number in the stamps. So how does 10 and 11 relate to 1999. From my experience with Japanese parts I knew that some manufactures use the traditional Japanese calendar for date stamps. The traditional Japanese calendar is based on the reign period of the emperor. The period from 1989 to present is called the Heisei Era. During this era the traditional Japanese year for 1998 is 10. The traditional Japanese year for 1999 is 11. Greg's gauge cluster was made in September 1998 and installed in a 1999 year Z. And of course, the number 11 on my gauge cluster means that it was made in 1999. You can learn about the traditional Japanese year at the link below. And below are some pictures of the date stamps. I also included a picture of the date stamp on the speedometer board mechanical gauge. That stamp is not the traditional Japanese format. The stamp says 980904 or September 4, 1998.
The traditional Japanese calendar explained.
[ http://www.ewc.co.jp/en/japan_info/calendar.htm ] 
Conversion to read MPH:
The speedometer board has three different IC chips. I'll call these ICs 1, 2 and 3. IC1 receives the speed sensor signal and splits it up into two different directions. One direction is a linear analog voltage output that is not used and the other direction goes to IC2 and IC3. IC2 converts the signal to either mph or kph depending on how it's pins are configured. It drives the mechanical speedometer gauge. JDM boards can be modified for mph and USDM boards can be modified for kph. One half of IC3 uses the signal to form a stepper motor driver output to drive the odometer stepper motor and the other half of IC3 outputs a 2 pulse signal to the ECU pin 53 so it can process your speed. That same output also goes to the hicas control unit pin 6, power steering unit pin 3 and the A/T control unit pin 27.
The pictures below are of Greg's converted speedometer board. I used a high strength epoxy to protect the modified sections. The cables going to the interface are double shielded.
 
Calibration:
After modifying the speedometer gauge for MPH it needs to be calibrated. The use of a signal conversion interface is needed in order to calibrate the gauge. This is because there are no external components that can be added or modified to make the IC that drives the meter do anything different. The operation of the IC is internally fixed. When modifying the board you must only intercept the signal going to the "metering" IC. The original signal to the stepper motor/2 pulse driver IC must be maintained to insure proper speed reporting to the ECU, HICAS and other modules that use the speed signal. After modifying the board to accept the interface and performing the calibration the accuracy is pretty much spot on.
Gauge cluster illumination:
The illumination of the gauge cluster is very low. In a lit room you can hardly tell they are even on. Because of that I thought I would try to see what difference it would make to change the lamps to the blue filtered bulbs, no filtered bulbs and LEDs. No filtered bulbs and LEDs were way to bright and the blue filtered lamps caused a little to much white light bleeding. I have some red LEDs but haven't got around to testing them out yet. Here are the results of trying different lamps under different situations.
Lamps blue filtering room light
 Lamps no filtering room light
 Lamps no filtering dark
 LEDs room light
 LEDs room light dimmed
 Lamps white filtering room light
 Lights off room light
 Lamps white filtering room light 2
 Lights off room light 2
Packing for shipping:
And I thought I would mention. For a while now I've improved the way I've been shipping back gauge clusters. This has been my prefered way to return them. These are pictures of Greg's shipment. I was also returning the interface and an extra odometer of his in the smaller boxes.
Many thanks to Greg for his help in bringing this together.
 www.mytwinturbo.com Nissan Data Voice - The first Nissan diagnostic software with a voice!
 Nissan Data Voice on YouTube Download my Nissan 300ZX Vin/Model Lookup. |
