Air core tachometer- GTC family
Tachometers operate by counting pluses from a signal source and interpreting this count per second. Once the tachometer has this number, it will move the pointer to the appropriate position on the dial. The tachometer is a relatively simple gauge only requiring power, ground and a signal. The tachometer signal source can be one of several items.
Negative side of the coil (high energy type)
CDI box (MSD output on the side of the box) This is a 12V square wave signal
Tach output on a distributor (HEI or similar) This is usually a high energy or hall effect signal
PCM pulse output (most commonly an open collector signal on GM PCMs) GM PCMs also output a 4 cylinder signal and a 10k-ohm pull up resistor will be required.
Pulse sensor on crankshaft, camshaft or flywheel. Most commonly an AC sinewave signal
Know where you are picking up a signal before proceeding, this will aid greatly in troubleshooting.
Before proceeding check the following:
Turn on the key. Pointer may "jump" it may or may not be exactly on zero. If not:
Check for power on the IGN wire
Ground on the GND wire
Signal on the SIG wire
Turn on the lights, if the lights do not work, there is not a ground,.
Check that the signal selection COMM PORT is properly connected
Gas vehcile cylinder selection
Follow the diagram in the INSTRUCTION BOOKLET
To select the peroper number of cylinders, the plug in the P2 position ont eh back of the gauge is to be used.
The COMM PORT is the wire that will select the number of cylinders. Connect thet wire to the cylinder selection wire required for your vehicle according to the diagram in the INSTRUCTION BOOKLET
Issue:
Tach does not operate at all
Tach does not read properly
Tach reads slowly
Tachometer climbs with power on
Vehicle will not start with tachometer installed
Tachometer is stuck on the high stop limit peg