Question:
How do I know if my tach is voltage-driven or current-driven?
Answer:
Typically, a current-driven tach will have a loop of wire on the back where it senses the current. Also, a current-driven tach is normally connected to the plus side of the coil, while a voltage-driven tach is connected to the minus terminal of the coil.
Question:
Can I use TachMatch with a positive-ground vehicle?
Answer:
Yes, you would connect power and ground in the reverse direction - and of course be careful to not touch the circuit board to anything during installation.
Question:
What's a pull-up resistor, and why might I need one?
Answer:
Often, ECUs have "open-collector" outputs. This can be viewed as a switch, with one end connected to ground. If the other side of the switch isn’t connected to anything, it stays at ground potential all the time – on or off. A pull-up resistor connects the other end of the switch to 5 or 12 volts so that when the signal is off, the output will be the 5 or 12 volts, and if the signal is on, it will be ground (0 volts).
Question:
What size pull-up resistor is necessary?
Answer:
TachMatch has a pull-up resistor built into the ECU input. But otherwise, one should use a value that is about 1 KOhm or more. Usually 10 KOhms is a good value. If the value gets too small, it could damage the ECU.
Question:
My tach reads a couple hundred RPM off from your 3,000 RPM test signal, and the potentiometer adjustment doesn’t help. Why not?
Answer:
The potentiometer adjustment is only active for vintage tachs. Standard tachometers operate accurately with the precise, computer-generated multiple of the trigger signal that TachMatch generates. However, you can calibrate standard tachometer output to correct for inaccurate tachometers with the engine-cylinder and tach-cylinder buttons - see the instruction manual for details.
Question:
Can TachMatch be used in other applications?
Answer:
Yes. It can generate frequency ratios from the input trigger signal. Anywhere from 1:8 to 8:1. Clever customers have used it to correct signal frequencies in other applications.
Question:
My tach doesn’t trigger from the TachMatch, why not?
Answer:
TachMatch generates a 12v signal. Some tachs rely on the big inductive “kick” from the coil. For this purpose we designed the V-Boost module. This is usually necessary for VDO tachs used in various makes and models, Jeep tachometers, and many of the Datsun Z-car tachometers.
Question:
If my tach has a different number of cylinders than the engine, and I need the V-boost to make the tach work, do I also need a standard TachMatch?
Answer:
Yes.
Question:
What size wire should I use?
Answer:
The slots in the enclosure are sized for #18 AWG, but other sizes of wire can be used.
Question:
Is the TachMatch compatible with Pertronix ignition systems?
Answer:
Yes, it is compatible with Pertronix installations except for the Ignitor III models.