1992 Mitsubishi 3000GT How to test Speedomitor sending unit

Hello -

This is what our manual states for the speedometer not working. . .. . .. . ..

Looks like it could be a broken cable or it is an electronic one the sensor could be bad. I have attached the check for both until you can see which type it is.

DESCRIPTION & OPERATION
Instrument cluster includes speedometer, fuel gauge and temperature gauge. Fuel gauge has a built-in voltage limiter to keep voltage supply to gauges at 7 volts. Some models may also have a shunt-type ammeter, oil pressure gauge, tachometer, voltmeter and/or turbo boost pressure gauge. Oil pressure gauge uses full battery voltage. The tachometer operates by pulse feed.

SPEEDOMETER NOT WORKING
Ensure speedometer cable is properly connected and correctly routed. If speedometer pointer and/or odometer still do not work, replace speedometer as an assembly.

SPEED SENSOR
Voltage Test (Stealth & 3000GT With Electronic Speedometer)
Remove speed sensor from transmission. Connect speed sensor, resistor (3000-10,000 ohms) and battery. See Fig. 32 . Using a voltmeter, ensure voltage pulses on and off 4 times per revolution of speedometer shaft. Replace sensor if voltage is not as specified.

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If you have the cable type. . ..here is the info we have on removal and installation of it.

SPEEDOMETER CABLE
NOTE: When routing speedometer cable, DO NOT bend cable sharply. Minimum bending radius is 6" (150 mm). Speedometer cable length varies with transmission type.
Removal
Disconnect speedometer cable from transmission or transaxle. Remove instrument cluster from instrument panel. See INSTRUMENT CLUSTER . Disconnect speedometer cable from instrument cluster and/or adapter (if equipped). Remove speedometer cable from firewall grommet.
Installation
1. Install new cable. Insert cable until stopper seats properly in groove on rear of speedometer housing. Pull speedometer cable through firewall grommet until cable marking is visible from engine compartment.
NOTE: An improperly installed cable can cause fluctuating meter, noise or damaged harness inside instrument panel.
2. Install adapter onto speedometer cable (if equipped). Install instrument cluster. See INSTRUMENT CLUSTER . Install cable onto transmission or transaxle. Check for proper operation.

Removal & Installation (Stealth & 3000GT)
Disconnect negative battery cable. Remove driver-side knee protector. Remove lower and upper column covers. Remove meter bezel and instrument cluster. Disconnect speedometer cable and connectors from back of cluster. Remove cluster. To install, reverse removal procedure. See Fig. 53 .

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Also, it looks like you may have some recalls on your vehicle. The dealer may fix these for free. Please contact the dealer service department, give them the VIN number of your car and have them check on these to see if they apply to you.