Greetings,

I am posting this in general tech because the various rules topics in the DIY forum are confusing and generally seem to discourage posting when open discussion is desired. That being said, this topic is far from general and is an attempt to elicit detailed knowledge if anyone who frequents the forum is knowledgeable on this subject.

For some background: I intend to use my knowledge of signal processing and computer engineering to design some gauge-shaped circuit boards which will take the place of the normal gauges in my 6th generation Accord. I intend the circuit boards to have a digital read-out and a ring of LEDs to mimic the speedometer needle. There is really no practical purpose in doing this, I am undertaking this simply because I think that it will look cool. I have purchased a spare set of instruments (Nippon-Seiki type) to work with. I intend to hook up wires to the cluster and read the Speedometer/tach/other signals using a PC-oscilloscope. Based on correlation of these signals to the readings on the stock gauges, I will design a program on an 8-bit microprocessor to run the ring of LCDs and digital readout on a character LCD. After that, I will get a small run of circuit boards fabricated (some places will do runs as small as 4 sets) and build the gauges.

Currently: The gauges are air core type gauges, meaning (based on my research) that they should be moved by two opposing varying current signals. It seems like it might be difficult to correlate these signals to the gauge readings, so I am looking for a way to access the raw signals from the tach and speedometer or perhaps other processed signals if they are available. I am also trying to figure out in general how the circuit board is set up and what happens to the inputs as they head towards the gauge needles.


My initial questions to the forum:

1. Does anyone have a diagram or listing of what signals enter each pin on the three green connectors at the top of the gauge cluster? (This would be a great help in figuring out what is going on on the circuit board.)

2. Does anyone have an electrical schematic of the NS instrument cluster circuit board? (I know this is highly unlikely, but I might as well ask. It might be in a book I can buy or something.)

3. In what other forms are the speedometer, tach, fuel level, and temperature gauge signals available and where near the cluster can I hack into them? (In the end, it might be simpler to hack into a raw signal rather than trying to interpret what the cluster is sending to the air core gauges.)


I intend to write down what discover along the course of this project and if I succeed, provide circuit board files, parts lists, programs, and a guide to the forum in case anyone else wants to try and pull off a stunt like this.

Thanks for reading, any help is appreciated.

 

You can download a 98-02 shop manual from the Online Manuals thread in the DIY section. That covers non-US accords, but they tend to be pretty close to the US version. You will have to verify the wire colors to be safe.

 

I am having some difficulty locating the 98-2002 manual. From the list of Accord manuals, the only one that seems close is the following entry:

Accord 1998-2000 CG7 CG8 CG9 CH1 CH2 CH5 CH6 CH7 CH8 CL3 ESM .iso EDM English German H22A7 D16B6 D16B7 F18B2 F18B3 F18B4 F20B6 F23Z5 20T2N(diesel)

I know that 98-2002 is a generation, all similar, but the fact that they specify 98-00 makes me think this may be the wrong file. I can't check the file itself until this evening. I also don't know if one of these three character codes represents "4-door Accord LX".

Could someone please help me interpret the manual listings, or point me to a place that has information on how to interpret them?

 

That is the link that I am talking about. I though it had 98-02 on the label. It is a free source for information. You could buy a shop manual as well.

 

Let me check my Haynes manual for #1 and #3 information. I completely understand what you are trying to do. Sounds like a cool project.

I know it won't have a PCB schematic... That is a cool question. I can ask my dealership if they can get one... Granted, shops don't seem to perform board-level repair.

 

I was able to identify three wire colors that I believe are the colors for the speed, tach, and fuel signal from diagrams in the digital manual that PA_honda linked. That manual had wiring diagrams, but they left the tach, speedo, and fuel level circuits as black boxes in the diagram. I need to get back home where I have that manual before I can post the colors I found.

From the diagrams it looks like it will be easiest to tap into the raw signals coming into the dash as opposed to interpreting the signals entering the air-core gauges.

The one thing still eluding me is the fourth gauge (temp gauge if I am not mistaken). There is a fourth gauge in the diagram, but in the diagram it's name was nothing like 'temperature' and unlike the others I could not trace it back to an independent wire color. It also seemed to feed into the oodometer somehow, which is why I questioned how it could be the fourth (furthest to the right) gauge. If it isn't, then I haven't found the temp gauge yet.

If you find similar info could you please post it too, so I can double-check my findings. I will post mine when I have the manual this evening.

 

manual is in the garage, i am looking at putting cruise control in a 1960 BelAir tonight, i can report the manual findings when i get back (manual is in the garage).

it had good schematics, but you may end up just having to pull the gauge and look at the board (hopefully it isn't more than 2-layer).

 

Oh, I pulled the board already. It's actually a one layer. The front side has no traces, just components and jumper bars used to link stuff on the back side. I am considering drawing off the raw signals because of what I found on the back of the board, which is basically a circuit that would take a few weeks to draw on paper (lots of traces and a good deal of surface mount components too small to read the ratings on). Plus, the ICs used to run the gauges only seem to have manuals in Chinese.

Anyway, the wire colors from the diagram I am looking at are:

Blue - Tachometer
Blue/White - Vehicle Speed Sensor
Yellow/Blue - Fuel Gauge Sending Unit

and then we have the really confusing one:

ECT Gauge: This gauge has three connections. 1. Inputs from the odo/trip/outside air temp drive circuit, which takes input from green/yellow, the outside air temp sensor. 2. Vehicle ground. 3. Ignition circuit via a 7.5A fuse (yellow). This is for power, I guess. The signals and setup provided in this diagram does not seem to match what I thought the function of the furthest rightward gauge is, so I am missing some important info there.

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On another note, i wonder if it would be feasible to use the air core gauges to turn a variable resistor and take a reading off that for the digital gauges. Probably not because the resistance to movement would be too high, but it's an idea.