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1967–1972 Chevy/GMC Truck Installation Manual

October 21st, 2009 · No Comments

Remove the Stock / OEM Instrument Panel
1) Make sure to disconnect the vehicle battery before you begin to remove the instrument panel.
2) Remove the two 5/16” screws which are holding the steering column tight to the base of the dash. This allows the steering column to drop down slightly.
3) Remove the six screws that are holding the panel to the dash.
4) Remove the light switch knob. To do this, push in the button at the top of the switch box housing (under the dash) and then pull out the light switch knob and shaft. Next, unthread the nut holding the light switch box to the instrument panel and remove the light switch box.
5) Remove the wiper knob. To do this, loosen the small set screw, pull the knob off and then unscrew the bezel.
6) Disconnect the speedometer cable from the back of the instrument panel.
7) Disconnect the oil pressure gauge tube (if equipped) from the back of the instrument panel using a 5/16” wrench. Be sure to protect your upholstery from any oil that may drip from the loosened oil pressure gauge tube.
8) Remove the large electrical connector on the back of the instrument panel by squeezing the lock tabs on the sides of the connector.
9) Remove throttle and choke controls from the instrument panel (if equipped).
10) The instrument panel can now be removed from the dash.
11) Please retain all screws, knobs and bezels to reuse when installing the new Classic Instruments panel.

Determine Speedometer Signal
Determine where you are going to get the speed signal for your speedometer. If your transmission has a port where a mechanical speedometer cable was attached, you will need a pulse signal generator. The GM style signal generator is shown below in figure 1. The pulse signal generator produces 16 pulses per revolution and has three connection wires. Typically, transmission speedometer cable gears produce 1000 revolutions per mile. Therefore; when using a pulse signal generator, you will need to calibrate the speedometer according to the 16,000 pulse per mile (ppm) chart on page 14 of this manual.

Wiring the Speedometer
Step 1:
Connect switched +12VDC from a dedicated source (we recommend the accessory side of the ignition switch) to the pink/white wire on the 6 pin connector [position B] of the instrument wire harness. If accessory of ignition is not available, connect to a switched and dedicated fuse on the fuse panel. This will help prevent interference to the speedometer from the power source.
Step 2:
Connect the red wire from the pulse signal generator OR power wire from the SN74 to the purple/white wire on the 6 pin connector [position B] of the instrument wire harness.
Step 3:
Connect a dedicated chassis ground (i.e. don’t stack with any other ground wires) to the black/white wire on the 6 pin connector [position A] of the instrument wire harness. This will help prevent interference to the speedometer from the ground.
Step 4:
Connect the black wire from the pulse signal generator OR ground wire from the SN74 to the yellow wire on the 2 pin connector [position B] of the instrument wire harness.
Step 5:
Connect the white wire from the pulse signal generator OR output from the SN74 to the purple wire on the 2 pin connector [position A] of the instrument wire harness.
Step 6:
If using the SN74 speedometer signal interface:
Connect one wire of the transmission VSS to the SN74 sensor gnd and the other wire of the transmission VSS to the SN74 input. OR Connect the speed signal wire from the ECM to the SN74 input.
Step 7:
If using the SN74 speedometer signal interface: Connect the two wires of the calibration pushbutton to the SN74 “pushbutton” positions.

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