280Z SpeedHut gauge conversion
I acquired some Speedhut gauges a while back for a deal, and I just got a free 240Z wheel, so I decided to do all three. In this part I just remove and fit the Speedhut gauges in the old speedo and tachometer housings. In the next part I wire them up. A few people did this on HybridZ various different ways. I was too cheap to go out and get any other supplies, so I made it work with what I had.
The gauges I got are:
Speedometer: 4" Revolution GPS Speedo with integrated fuel gauge, turn signal LEDs, and high-beam LED
Tachometer: 4" Revolution 8,000RPM with programmable shift LEDs.
Both have red dials, and red illumination. The fuel gauge is there since I’ll be replacing the one in the 3 small dash gauges eventually, but don’t want to lose having a gas gauge.
Removal and Replacement
I never looked at the service manual and just assumed that the dash would have to come off to install the gauges. Well, after reading some other posts about it, the dash can stay in. But still I thought I’d have to lay upside down and it would be incredibly difficult to remove the gauges. Then I read the service manual: 2 screws. Two screws for each gauge, and only one each under the dash.
Easy. I had them out in less than 15 minutes. I removed the gauges and after fitting the Speedhuts, I realized that to install one of the gauges, I’d have to remove the steering wheel. Seeing as how my current steering wheel is gross, I picked up a free 240Z wheel and horn cover from a friend. It’s a little rough, but a lot better than my current one.
So, here’s what I did. It’s probably not the best way (at least the tach install isn’t), but I think it will work fine. I installed the new speedometer in the 280Z tachometer hole (the turn signal and high beam indicators are on the speedo, now, so I figured I would keep them on the same side). So, the new tachometer went in the old speedometer’s hole.
Speedo
After you remove the old tachometer gauge, gut it. For me I had to press the old tachometer mechanics off from the inside of the housing. The 280Z rear bumper came in handy yet again.
Next, I removed the turn signal indicator tubes from the housing, using a Dremel and about 50 of those stupid cutting wheels (okay, just 2).
After that I test fit the new speedometer to see how I would keep it in place. Those white plastic screw holders will be what I use. But first I put some grommets in place for the new gauge wiring:
The connectors for the power and light connections were a tight fit, but they went through the bottom there eventually. The rectangular fuel gauge wires fit nicely in the rectangular hole. I put a round grommet through the rectangular hole and it worked out.
Next I took all the wires out and placed the gauge’s threaded ring in there. Just my luck, it fit snuggly, and the gauge itself fits beyond the housing’s screw retainers, so I decided to tighten the gauge against those. However, I took each retainer out and clocked it 90 degrees, to avoid the ring compressing the retainers together (they are the ‘squeeze to remove’ type).
Then I placed the gauge in the housing, and tightened the ring down using a flathead scewdriver through one of the unused holes on the edge of the housing. It took a little while to make sure it stayed in the correct position.
The GPS antenna is on the metal portion of the dash, for now. It’s routed to the driver side A pillar, and down into the dash from there:
Tachometer
Remove and gut the old speedometer housing.
This one took a bit more convincing to remove the tubes. This was the plan:
But in the end, it was just too small to house the new gauge. So, I ended up cutting the back out and molesting the housing. For retention, this housing used tiny screws to secure it to the plastic cover. They weren’t long enough to extend and catch the threaded ring on the new gauge, so I looked for some longer ones. Long story short, I used screws from an old computer (laptop case, most likely):
They were just long enough. After a bit of finnagling, here it is installed:
Cute, huh?
For both gauges I had to drill holes to be able to access the configuration/mode buttons on the gauges. I tried to make it look decent:
And here’s the new tach, ready to wire up:
And here’s both of them:
Wiring
Now for the wiring. This would be easy except Nissan decided not to label their diagrams with the gauge-side harness wire colors. That is, the wiring schematics and diagrams tell you what color the wires are right up until the connector for the gauge or light or whatever. So you have to hunt in the dash for the wiring harness' connector and match them up.
But, if you have a 77 280Z (Cali model), I can make it a little easier:
B = Black, L = Blue, R = Red, G = Green, O = Orange, GL = Green with blue stripe, and so on…
| New Gauge Side |
|---|
| Power - R |
| Power - B, Lighting - B |
| Power - W, Lighting - W |
| Tach - Y (coil signal) |
| Speedo - LW (high beam indicator) |
| Speedo - GR (right turn) |
| Speedo - GO (instructions say GY) |
| Fuel - W |
| Fuel - B |
*The stock 280Z high beam indicator will not work as is. It will be on all the time if hooked up directly. It must be switched on, perhaps using a relay like me. The problem is the stock system routes power to the lights and the indicator at all times, it’s the ground that switches between high and low-beam. The indicator is supposed to be activated only if the high-beams are grounded. That is, the indicator shares the same constant +12V power and ground as the high-beams. If you attach it to the gauge, there’s a path for current to flow to ground through (the gauge ground), and it will illuminate.
**Fuel Gauge: The stock fuel sender has roughly 8 Ohm Empty, 240 Ohm full readings.
***Parking Brake: I routed the parking brake light wiring to the floor temp bulb. Now if I leave the parking brake on the otherwise useless floor temp light illuminates (California model).
Now on to the details. First I hooked up the Speedhut power and lighting harnesses. I wired both the inverters and power wires together (both gauges, so 4 harnesses altogether). Power to the bare green from the old speedometer power wire, a ground, and the white lighting wire to one of the green-white stripe wires from the old gauge lighting.
For the high beam indicator, some work is required. You have to have a normally open relay added. Power the relay coil using one of the dash lighting wires (GW), but also tap this for the power to the switch. The other, open end of the switch should go to the high-beam LED of the new gauge. The ground for the coil should be the stock 280Z headlight beam indicator. Mine never lit because the high-beams have a short, I believe. The new one doesn’t light either! Success! Just kidding this might still not be correct.
For the new tachometer you’ll need to connect to the red/black wire. Turn signals are easy, white/black is right, white/red is left. There’s another ground and IGN wire here as well. I didn’t use them, so I cut and heat shrink insulated them.
Since the new Speedhut speedometer didn’t have a connector for the turn signals or hot start wire, I added a weatherpak. The high-beam indicator also doesn’t have a connector, but I attached it to the relay using a quick crimp connector. So, the weatherpak is a 3 hole, the middle is the hot start wire, the sides are the turn signals.
Now if I ever need to take it out no wires need to be cut.
The hot start is routed to the power for the radio.
I cut the gauge side harness of the old fuel gauge to wire in the new one. I shortened the included harness from Speedhut considerably. It came with 5 feet or so of wire, I shortened it to about 1 foot. This is the only time I found the gauge side harness colors to match the chassis harness. I thought it to be a trick, but it works.
Note that the stock low fuel warning light is still connected.
That’s it. It was pretty straightforward.
Calibrating through the holes was a little akward, but not hard. If I could do it a second time I would just drill one hole in the tach’s window, rather than the two. There’s room to move from one to the other without going to the other hole, and it’s faster anyway. That’s meaningful because you have only 2 seconds or so before it exits configuration modes.
Here it is it a very bad picture. 0 miles, and I haven’t set the correct tach pulse per revolution yet.