Today while the carpet installers are installing the carpet downstairs I decided to see if I could modify my stock fuel sending unit to work with the new gauge cluster. When you pull the stock sender out, bend back the three tabs that hold the little tin cover on. After you get that done, you should have something that looks like this.
Before you go any further, I want to remind you that this assembly has most likely been sitting immersed in fuel. I would recommend that you spray the sending unit with electrical parts cleaner and let it dry completely. You don't want to be catching yourself on fire here. :: angry :: Also, I get the feeling I need to say this as well. Don't do this around the gas tank. Anyway, now that my conscience is clear, lets move on.
See the wire that is soldered to that post? you can see it curling around the rod down to the Low Fuel Warning Sensor. Unsolder the wire from the post and unscrew the two screws that hold the post on. That whole assembly isn't needed for the digital dash.
Now, flip the whole assembly over, You will see 2 more posts at the top. One is connected to a piece of metal leading to the resistance circuit and the other is connected to a green wire going to the wiper assembly. For a reference, see below. JDM sensor is on the right, the sensor we are working on is on the left, with the yellow sleeve over the harness:
Now, if you look closely, you will see a notch in the top right side of the resistance board. Take a look at this picture for help:
Sorry, I had to do all this in photobucket and apparently you can't draw straight lines in the editor.:3d_frown: Anyway, that notch is there to hold the end of the resistance wire to prevent the whole coil from unwinding. You will need to take a small flathead screwdriver (like a jewelers screwdriver) and pop out the wire so you can unwrap it ONE revolution. When you are done, it should look like this:
The camera had a hard time focusing on just the single strand of wire, but hopefully you can see what I'm talking about. Now, that wire is covered in an enamel coating for insulation. You will need to take some 300-400 grit sandpaper and CAREFULLY sand off the insulation about 1/4" from the end. It will look shiny when you have removed the enamel.
Remember the green wire that went to the wiper? You are going to unsolder that wire and solder it to the post that the Low Fuel sensor was hooked to. It should look like this when you are done:
Now, flip it back over so you the resistance board and wiper assembly is facing you. Take that sanded piece of wire and solder it to the post that the green wire was formerly connected to. It should look like this when you are done:
At this point, that resistance wire can gradually slack up. You don't want that. What you will want to do is apply some gasoline-safe adhesive to the backside (the side away from the wiper arm; don't let anything get on the wiper arm or the wire surface that it actually wipes) so that the wire remains coiled up nicely. I used Eclectic adhesive from Autozone.
Now, you may want to plug it in the tank and enjoy your working digital dash fuel gauge. Don't. The pinout is different and you don't want to fry the gauge (smoke) or the sender (boom). You need to swap 2 pins over. As you are looking at the sender connector (male pins facing you), top left is Yellow with a Green stripe, top right is White with Black stripe, bottom left is Black, and bottom right is Red with Blue stripe. If you look closely, the connector is a front-release connector, which for this situation means that you can take a small jewelers flathead and going above the pin, lift the plastic tab holding it in and pull it out the back. Do it for the top left and bottom right pins. When you are done, it should look like this:
Now switch places of them. It should look like this now:
Put the Red with Blue stripe wire in the top left and the Yellow with Green stripe in the bottom right. Place the tin cover back on the sender and it should resemble this:
Install the sender back in the tank. If your tank is a couple gallons short of full (like mine is) it should look like this:
and save you from having to source (and overpay for) a ridiculously hard to find part. Enjoy!
A-to-the-J, I am probably going to do that. I have a spare main display board so I'll make the modifications to light up the correct legends and buy the 8:5 ratio electronic speed converter for the vehicle speed sensor. The converter is around $60, so I guess it is a small price to pay to have a dash that shows the correct speed. What I really liked about this swap though is my cruise control finally works!::w00t:: I think while I have my dash out, I will wire up the ECON, PWR and MANU lights to my HKS EVC1 so when I hit the buttons for the different boost levels, the corresponding light will come on in the dash. Kinda dumb, but I like the idea. Those lights are for the automatic transmission as far as I know, and I'm running a manual. Anyway, while I was walking around the junkyard yesterday, I found a late 80's Subaru GL-10 (Loyale I think) with a digital dash in it. I pulled the dash out, and lo and behold, it is made by Nippondenso! It has a very similar digital speed sensor with the 20-slot wheel. It even had the mostly the same part number on the board, 457652. The supra one is 457652-2002 and the subaru one was was 457652-2167 (I think). Anyway, they are mostly the same layone but more importantly, the Subaru one has a jumper on a 2-pin socket. When you pull the jumper off, the gauge switches from MPH to KM/H as well as the ratio. I verified this by hooking the speed sensor to a drill and spinning it. With it on MPH, I read 62 MPH and with KM/H it showed 105 KM/H. I followed the trace back to pin 19 on the Toshiba TC9500AP-814. It is a large 64-pin IC and if that pin is brought low, it switches from KM/H to MPH. I'm guessing it is some sort of microprocessor, but I can't find a data sheet online. I'll do some more digging today and see if I can find something on it. It would be awesome if that was the case though, because it is probably similarly designed on the Supra board and maybe I can make it work.
Edit: I think the chip number on top is a proprietary number. I think it is actually TMP87C814, which would make sense since it is an 8-bit microcontroller combined with a VFD driver. Now, to figure out how to get the Rom image off...
Interesting info on the processor. The danger is the MCU is proprietary, and therefore there aren't any publicly available development tools. That was the case for the ECU where the MCU is also fab'd by Toshiba.
Maybe I am missing the point, but isn't there a different speedo adapter you can put in the tranny to make the change? Also, what does the odometer do? Is it in kms or miles?
Well, the way the system is set up, the standard cable runs from the trans all the way up behind the dash to the speed sensor. The sensor has a 20 tooth optical wheel on it. Now, the odometer is in kms along with everything else. I could just cut the pins tha illuminate the KMS and KM/H legends and reroute the power to the MILES and MPH legends, then either make a 12-tooth optical wheel or find an electronic speedo converter from here or here to down convert the frequency to MPH. Since the stepper motor odometer is driven off of the speed signal from the sensor, dropping the ratio with the converter would automatically make it read correctly. I will probably just do this option since it seems to be the most idiot proof, but I was hoping that I could somehow reverse engineer the board a bit and maybe discover a pin that if brought low (or high) would switch it over to MPH like the Subaru dash. I guess these dashes are like apples to oranges though. I was hoping for something more like fuji apples to granny smith apples.
Awesome, thanks everyone! Dave, I have this big issue with doing modifications I can't undo, so for this I just spliced into the existing harness and kept all the old connectors. My thoughts were that if I ever wanted to switch back to the analog dash, I remove the digital cluster, speed sensor, swap out the fuel sender to the analog one, and install the old dash. Shouldn't take more than half an hour then it goes back to stock! I might start modifying the stock harnesses for the digital dash if there is enough interest. I have to finish selling the house though. It went on the market yesterday.
Hey thanks a lot Eric! I took a lot of info from your thread and without it, I couldn't have done what I did! Hopefully some of the info here will be helpful to you as well. I would like everyone else who does the conversion to post a picture of their completed swap on this thread someday too. I think that would be pretty nice.
So now everything is working great but I can't leave well enough alone. Living in the US and being stuck with gauges that read in KPH is a bit of an inconvenience. Well, this past week I rectified the situation. First, I used the instructions found here and lit up the correct legends. Now, that doesn't do any good if the numbers displayed aren't accurate! To fix that, I had to modify the speedo sensor. The stock one looks like this, with a 20-slot disk.
Now, I figured if I just made a disk with a fewer number of slots, it would display the correct number. for that, I noticed that 60mph is really close to 100kph. Divide both those numbers by 5 and you are left with 20 and 12. If I made a disk with 12 slots vs 20, it should display the correct speed. I designed one on this website and crudely cut one out of some plastic that I had laying around. It isn't the most pretty solution as you can see here:
I know it doesn't look the best, but after I put it all back together, I went for a drive and verified the speed with the GPS on my headunit. It works!
It is funny that they didn't. Probably had something to do with health and safety BS. I have developed this irrational hatred towards you guys with your awesome cars that you can get now. We still have to wait 10 more years to get the R34 and such. Grumble Grumble...
Thank you sir. I felt the same way while working this project, which was why I did the conversion in such a way that if I ever want to swap back to the analog gauges, it won't take me more than half an hour. I soldered the new connectors onto the stock dash harness and figured out how to modify the stock fuel sender so it will work with the dash. Since running this though, I don't think I will go back to the analog gauges though. These respond way faster, especially the oil and boost gauges. If I run low on oil pressure, I want to know now, not 15 seconds after the fact haha!
Yeah, it is a good thing! My next order of business is to figure out what makes the digital dash dimmer different from the analog dimmer. The digital one has 6 pins but the analog one only has 3. They are both electronic, so I'm assuming that the lighting is dimmed via PWM. I read that the digital dimmer has a setting to bypass the VFD dimmer when the lights are on as well. I know the panel lights and actual glass displays dim independently. It will take more research I guess.
Small update. I did some experimenting and figured out that in order to give the correct pulse count for MPH, each rotation of the wheel has to put out 10 pulses. It seems like if would be pretty easy to glue 10 small magnets on an axle and then position a small hall effect sensor next to them. I had to do that to my Delorean when I added cruise control to it. They didn't come with cruise control from the factory. This way may end up being a better solution because it doesn't matter what diff ratio you have. The speed will be accurate unless you run different diameter tires.
Another thing I did was change the panel dim wire. Normally, the panel dim wire is tied to the running light circuit. That means, whenever the running lights are on, the panel is dimmed. I like to run with the running lights on all the time. To get around that, instead ran the panel dim wire (blue wire, pin 12 on the 20-pin connector) to a headlight fuse in the engine compartment. Why couldn't I just connect it to something inside? Well because the headlight switch grounds the headlights to turn them on. If you refer to the TEWD here the headlights are always getting fed 12 volts when they are turned on, then the dimmer switch inside just chooses which pin to ground (high or low beam). The panel dimmer takes a 12 volt signal to dim the display. Now the panel stays bright until I actually turn the headlights on.
I thought about using the ABS wheel sensors but how many teeth are on the wheel?
I would love to make a custom sensor that just screwed onto the transmission where the speedo cable normally goes. I really don't see a good reason why the cable goes all the way up behind the dash when you could just run 3 shielded wires down to the transmission. I'm sure Toyota had their reasons...
Grant, correct me if I'm wrong, but I think the speedometer is driven from the ECU over a bus-type system. Programming the ecu via the OBD-2 port would make that pretty convenient. I need to do that with my larger tires on my Tundra actually! I've just been lazy. Pi, I am actually trying to learn programming with microcontrollers. I bought an Arduino Uno a couple weeks ago and have been going through the projects one by one to learn the coding. Another thought that came to me was using something along those lines with a GPS receiver. I'm assuming the coding wouldn't be too tough to just read the GPS signal and turn it into pulses. I haven't read about interfacing GPS yet however (I'm a big noob when it comes to programming). Plugging in the stock tire size and revolutions per mile gives me 811.32. Move the decimal over 1 because the system reads 10 pulses per revolution and I get 8113 pulses per mile. That should be pretty easy. I almost find that to be the best solution. It would be very easy to program in a switch as well in case you wanted to read KM or MPH. I guess I need to do some more reading.
Yeah, that seems to be really convenient. My 05 Tundra is a bit more of a pain in the ass since Toyota has a habit of locking down their ECUs. I have larger tires on my truck as well and I guess I just have to deal with it. Most people install some speedo corrector in the wiring but I hate the idea of installing something additional to take care of what I should be able to adjust myself. I can understand locking down the data that deals with driveability and such but they should know that people like me want a "Man Truck" and are going to customize their trucks to look tougher. Just make it easy on us to change tire sizes!
Anyway, yesterday I discovered something really cool as far as speed inputs are concerned. Like I said earlier, to display the correct speed in MPH, you need to modify the stock sending unit from 20-pulse to 12-pulse. Thankfully, Ford has been using a sensor that does exactly that! The 1994-1998 Mustangs use a VSS on the side of their transmission that ouputs the 12-pulse per revolution signal we need. On top of that, they are dirt cheap! On Rockauto, I'm seeing new ones for under $15. The part number is SC37T. This is what it looks like:
Now, there is a small issue. This is a VR-style sensor. It puts out an AC sine wave. The dash needs a 5v square wave to function properly, so for that you need to make or buy a VR-conditioner circuit. I would buy the Brick VR conditioner/ because it is small and also because it runs on 5 volts. This will convert the AC signal to a more friendly square wave signal for the dash. The convenient thing about running this speed sensor arrangement is that you no longer need to run the speedo cable all the way up and around to behind the dash. You can just run a few shielded wires down to the sensor near the transmission. This is environmentally sealed since it was designed to be used on the transmission. It will handle most anything you dish out.
Man, I haven't been on here in months! Moving and getting settled in took more time than I thought! Anyway, as far as the sensors go, they are close to impossible to get ahold of, since the Japanese junkyards don't think of pulling the speed sensor when they pull the gauge cluster out. In post 42, I detail the procedure to convert your standard analog fuel sender unit to work with the digital gauge cluster. As far as the digital speed sensor goes, you can't use the Marlin Crawler unit (trust me, I tried. At only 4 pulses per revolution, it would be drastically off! The stock one is 20 pulses per revolution. If you want it to read in MPH, you need to find a sensor that puts out 12 pulses per revolution. A couple posts above (post 73) I talk about the speed sensor. Seeing your location, I can only assume you need the speedo to read in KM/H. I did find a few 80's Japanese cars in various junkyards that had digital gauge clusters. I think it was a late 80's Subaru Leone that had a digital dash where the sensor was a 20 pulse per revolution sensor. Nippondenso made the digital clusters in the Leone, XT, and Loyale, so the sensors are all most likely pretty identical. One note of advice though. The sensor on the Supra used a 5v signal and had a built in regulator in the sensor itself. The Subaru one doesn't have that. If you directly hook up the subaru speed sensor to the supra dash, the higher voltage will burn out the sensor and ruin it. You will instead want to run a 150-ohm resistor inline with the 5v input.
No problem! I'm here to help! I'm hoping to start building more conversions as things start settling in. The problem is finding female analog dash connectors. I want to make a convenient solution for anyone to use.
Oh nice! I don't know where you can buy them new. I know they are similar to some of the connectors on the car already, like ABS and some others. I think I listed them in here somewhere! I'm on my phone and so I can't find conveniently find it.