This is a write up on how I modified a stock mr2 NA tachometer to read a v6 engine signal properly.
I read that a 97+ Camry tach is a direct replacement for the mr2 one but I was unable to locate any at the junk yards so this left me with only two options: installing an aftermarket tach or modifying the stock tach. I didn’t want to give cops any more reasons to pull me over and now that I’m older it looks sort of silly to me now so I went with the latter option.
Here are the websites that I found helpful for this mod:
TOYOTA TACH MOD
MR2 Wiki - MKII:3vzfe TACH browse
Non-turbo tach – This mod was done on a non-turbo tach so I don’t know if it will work on a turbo tach, but I don’t see why not.
10k or 5k ohm 15-turn trim potentiometer – radio shack $3
22k ohm resistor ¼ or ½ watt 5% tolerance – radio shack $1
Hot glue gun and glue stick
Quick splice connector (Scothlock Connectors.)
Wire stripper and cutter
This modification could possibly leave your tach non-functional. Do not hold me accountable for what you do to your own car. Proceed at your own risk.
Okay let’s get down to business.
Step 1: Remove the combination meter from your car and remove the front plastic cover to get access to the gauges– please refer to the bgb for this step.
Step 2: Flip the gauge cluster over and remove the three screws holding the tach to the gauge cluster. You should see SE, M+, and M- next to the screws. After you remove the screws the tach gauge will fall out of the front of the gauge cluster.
Step 3: Using your multi-meter set to read 200k ohms find the 43k resistor on the tach circuit board. It’s the biggest one there. Now use your soldering iron and remove the resistor from the circuit board and replace it with one of the 22k resistors you bought. The orientation of the resistor doesn’t matter so don’t worry about it.
Step 4: Using your multi-meter again, find the 7.5k resister. It should be the second largest one compared to the 43k resistor. It might even be the same size, I don’t know because I threw them out already. Use your soldering iron, remove the 7.5k resistor and replace it with the trim potentiometer. The potentiometer has 3 leads. Use the middle one and the one furthest away from that. You will have to bend the pins out some to fit it in the holes in the circuit board. Be careful with the pins because they break off easily. Break the unused lead off of the potentiometer and secure the potentiometer to the circuit board with the hot glue gun while making sure that the leads on the potentiometer aren’t touching any other connections on the circuit board.
Step 5: After calibrating my tach I ended up with a resistance of 3.27k on the potentiometer, so as a base line you should use your multi-meter, set it to 20k ohm, and adjust the potentiometer via the little screw head to 3.27k. This way you wont have to do a lot of adjustments on the car.
Step 6: Don’t install the tach gauge back into the cluster you wont be able to adjust the potentiometer that way. Take the 3 screws that you removed from the gauge cluster to remove the tach in step 2 and tread them half way into the holes on the back of the tach gauge circuit board where it says M+, M-, and SE. Use quick splice connector and some wire to splice into B3 on the B connector of the combination meter wiring harness. This will be your tach signal. You will also need a +12v and ground connection. I removed the connector on the back of the cigarette lighter to get the ground and power connections. Run two wires into this connector and use your multi-meter to test them to see which wire is power and which is ground. If you can’t remember, label them.
***Warning*** the repair manual says that you should never let the tach signal touch ground while the car is running, so be careful!
Step 7: The stock tach gauge has 3 screws/terminal posts: M- (Tach signal), M+ (+12v power), SE (Ground). Your aftermarket gauge should have these same connections plus one extra wire for the backlight. You can hookup the backlight wire to the +12v power wire or leave it unwired. Now just connect both gauges up using the wires that you ran in step 6 and tape all the connections up with electrical tape.
Step 8: Now start the car and hold it at a steady RPM and adjust your stock tach to match the aftermarket one. Make sure you use different RPM points to calibrate. I used 1k, 2k, 3k, and 6k. Keep an eye on both gauges as you rev to see if the stock gauge is more or less doing what the aftermarket one is doing, adjust the potentiometer with a flat head screw drive as necessary.
Step 9: After you are satisfied with the calibration of the stock tack turn off the car and disconnect both tach. Remove the power and ground wiring. You can also remove the tach signal wire if you want but I left it there with the end taped up incase I wanted to install and aftermarket tach in the future. Make sure you tape it up with electrical tape and label it so you know what it is later.
Step 10: reinstall the stock tach back into the gauge cluster and reinstall everything back in your car the reverse way you took it apart.
That’s it. I tried to be as detailed as I could but if I missed anything please let me know.