Hi, I'm getting an alarm put in the vehicle, and they need to grab info from the tachometer wire - but they can't find it. Also, they tried talking to the local Mazda dealership, but they also didn't have the info.

Does anybody have any schematic info they can post / scan / e-mail that would help?

Thanks.
-Nick

There IS no "tachometer wire"

You can derive it from one of the plug coilpack trigger wires, and multiply by two.

There are 4 plugs. 2 per rotor. One leading and one trailing.

On the ECU connectors pugs, on the 28 pin plug, the lower left connection, with the white wire is the front rotor, trailing coil trigger. The blue with orange wire above that is the rear rotor, trailing coil trigger.
next to these ( inboard one wire), are the leaading coil triggers. yellow/green and green wires.

Cool, thanks for the info.

I'm a n00b....what does tach have to do with the alarm?

thx

canzoomer - i guess i don't quite understand exactly what the remote start is supposed to detect through this single "tach" wire that is hooked to the trigger(s). if i knew that i could prolly work through it myself and not have to be a pest. essentially, i was just going to hook it up to one of the trigger wires and see what happened.

i don't necessarily need the answer, but can you maybe give me a clue as to what exactly you meant by "derive it and multiply by two."?

The coil trigger wires come from the PCM. It puts out a +3V 5 mS pulse. To get true RPM you need to multiply by two, or add the pulse from both rotors (leading or trailing). If you are just detecting "engine run" (I suspect that is what that wire is for), you don't need to worry about that, just use one trigger wire. Put a diode in series and a resistor. Try 10K to start. If it doesn't trigger the unit you are installing, try dropping the resistance value by half. I wouldn't go any lower than that. We use 1N4148 diodes.

rx-8 friend is a friend indeed! thanks for your assistance. i will give it a shot and report the results. kevo

I now understand that the CZ unit will be coming specifically with a tach output (according to a post from Canzoomer). Any info on the format for this interface, so my alarm installation guys can start working on it?

The tach output is a pin which has, coincidentally, a diode and resistor from each rotor leading ignition output, tied to the pin. It is a true tach output (RPM=true RPM). With a high impedance input to whatever you connect to it, you should see about +2.1 V 5 mS pulses. It uses 10K ohm resistors. The rotary gives you a pulse rate just like a 4 cylinder engine, so you get two pulses per rotation.

sweet success! tach was detected with a IN4148 diode and 10k resistor in series hooked to a single coil trigger. the transponder bypass installed without a hitch and remote start is up and running. now i just have to find the factory arm/disarm wires that don't also fire the door locks and i am in business.

thanks again rx8-friend and canzoomer...i couldn't have done without you guys! kevo

see the following thread...

http://www.rx8club.com/showthread.php?s=&threadid=25928