BrillianceLin

Hi, I believe I am not the only one frustrated about DX trim level does not have tacho meter. Well, that is always way out, and the following information is one of them. The installation method I used is more of parasitic method than modification method. The advantage of this method is the installation is totally reversible. It means if you do not want the tech anymore, you can remove it without damaging any insulation of existing wire harness. But since I have yet to confirm the reliability of this installation, using it is your own risk. And please make sure you disconnect the negative lead from your battery and wait for 15 minutes before carrying out any of the following operation.
First, begin with the removal of steering column cover. Do it as per maintenance manual instruction. However, neither Honda official maintanence manual nor Haynes maintanence manual clearly describe the detail of dettaching upper halve and lower halve of the steering column. I suggest using a long enought flat head screw driver (20-30 cm) to release the latch right on top of the steering column adjuster handle. Otherwise, that latch is going to break if anyone attemp to rip the whole thing apart by force. And I found out this the hard way.
Second, remove the gauge cluster bezel by removing two screws on the top section of the bezel, that will allow you to squeeze your hand between the bezel and the console. Then slide your hand to one side as far as possible (it is gonna hurt, but hang in there). You will need to use the other hand to grab the bottom of the bezel from the open section of steering column (make sure you grab the bezel firmly and do not rely on the skirt of the bezel) and yank out one side of the bezel. You will need to do the same thing for the other side of the bezel. Honda only use two quick release clip to hold the bottom of the bezel. They are not that easy to break because they are made of steel, so do not worry.
Third, you are now able to access to gauge cluster connectors by removing 3 screws on the gauge cluster. For DX trim level you will need to look for following wires

Right connector- Green (WRT face toward gauge cluster and connector wire side)
Blue wire-tach signal wire (top row 3rd slot from the right/ slot 13 from honda maintanence manual)
Black wire- common ground G501 (top row 6th slot from the right/ slot 16 from honda maintanence manual)
White and red wire- master switch control circuit (top row 5th slot from the left/ slot 18 from honda maintanence manual)

Left connector- light Blue (WRT face toward gauge cluster and connector wire side)
Red and Blue- Head light (bottom row 1st slot from the right/ slot 1 from honda maintanence manual)

Function:
Blue wire- tach signal to give you reading on tach gauge
Black wire- common ground G501 to complete all your circuit
Withe and red wire- master switch control circuit to power your tachometer when you turn on the ignition.
Red and Blue- Head light to give you control on tacho meter lighting

Note 1: the way honda install these connectors is upside down wrt their maintenace manual. (top row when you physically look at the connector is the bottom row of the connector shown on the manual)
Note 2: for constant lumination gauge, tap in the head light wire is optional
Note 3: Red and Blue wire voltage is zero when high beam engauge (hence you need to tap in the gauge lumination wire for Non-constant lumination gauge)

To tap in these wires, you will need to buy some pins from electronic store. The pins I used are 14.9mm overall length with 1.01 mm pin diameter. Crimping tools for these pins is highly recommend to purchase. It will directly effect the reliability of your connection.
Upon you complete crimping Pins on the harness (attached pic 1), you can insert your pins into the desire connector slot. After you put all pins in, your tachometer should have been parasitically attached onto the host circuit and should be able to be reomved as you will. When you done your continuity check and instrument test. You should be good to put everything back together and enjoy your tach. The harness come with my tach is not long enough, therefore I need to crimp some extra connector to extend the legnth of the harness (attached pic 2). It turn out this increase the maintainability of the new installation in some degree.
Althought the space for the cluster comparment is tight, there is still possibility to fit in few more connector as for better manage the relationship between the parasitic circuit and the host circuit.
Sorry for lack of photos, I was in a rush to put everything together at the end of this project.
I hope this information will help.