Benchtest Speedometer Gauge Cluster

NOTE: This article is a WIP. This notice will be removed when completed

The point of this article is to figure out a way to fully bench test a 91-92 style speedometer cluster to determine if the cluster is bad, and needs repair. More information on repairing them will be implemented through separate posts once at that stage.

Here’s the outline of necessities to fully power and test the cluster:

1) Source power (12-14v DC)
DC Power Supply Variable, Eventek KPS305D Adjustable Switching Regulated Power Supply Digital, 0-30 V 0-5 A with Alligator Leads US Power Cord

2) Frequency generator (Square wave, not Sine)
Koolertron 30MHz DDS Signal Generator Counter Upgraded, 2.4in Screen Display High Precision Dual-channel Arbitray Waveform Generator Frequency Meter 200MSa/s (30MHz)

3) Oscilloscope to verify signal prior to going to speedo/tach
Rigol DS1102E 100MHz Digital Oscilloscope, Dual Analog Channels, 1 GSa/s Sampling, USB Storage


4) Potentiometers (3 in total):

Fuel Gauge requires 0-90 ohms (verified for 5.0l cars, unsure about 5.7)
0ohms @ empty
90ohms @ full
Jameco Valuepro PW24-B100-R Potentiometer Linear Taper 5W 100 Ohm Wire wound 20% Shaft, 0.235″x.67″

Coolant Temp requires 0-1365 ohms (this is the same between 5.0 and 5.7 cars)
1365ohms @ 100F
55ohms @ 260F
Uxcell a15011600ux0239 2 Sets 1K 2K 5K 10K Ohm Linear Taper Rotary Potentiometer Pot

Oil Pressure requires 0-90 ohms (this is the same between 5.0 and 5.7 cars)
0ohms @ 0psi
90ohms @ 60psi
Jameco Valuepro PW24-B100-R Potentiometer Linear Taper 5W 100 Ohm Wire wound 20% Shaft, 0.235″x.67″

5) Jumper Wires w/alligator clips
WGGE WG-026 20 Pieces and 5 Colors Test Lead Set & Alligator Clips, 20.5 inches

6) Diagram for cluster pinout on back
What I’ve noticed is most cluster connector printers are orientated so that it is described with the cluster FACE DOWN, with the pins facing towards you. Use the diagram shown here for 91 cars 5.0l. I sourced it from google images, AustinThirdGen.org created the image

 

Now onto hooking all this stuff up! I’ll provide separate instruction sets for each gauge to test

TESTING THE SPEEDOMETER, ODOMETER, and TRIPMETER

First we need to setup the frequency generator and source power before connecting it to avoid any damage.

  1. Turn on your frequency generator to produce a square wave. Offset the voltage to 2.2-2.5v so it creates a 0-5v on/off square wave, and set the HZ to 0 for now.
  2. Turn on your voltage generator and make sure it’s set to 12v DC. Then turn it off.
    (Mine shows higher 13.7v since this is the only picture I have available and it’s during the testing)

Now to make the necessary connections. There are only 3 connections required for this. +/- and speed input.

There will be 2 wires coming from your frequency generator:
red wire to the #1 pin (SPEED INPUT)
black wire to the #2 pin (GROUND)

There will be 2 wires coming from your voltage generator:
red wire to the #14 pin (GAUGES POWER)
black wire to the #2 pin (GROUND)

Turn on the voltage generator and adjust the amps/volts as necessary to bring it up to 13.4v~ which is engine running voltage.

Turn on the frequency generator, and start cycling the HZ from 1-130HZ. As you go up in HZ the speedometer should increase in speed. As the speedometer is active with a speed, the trip meter should be moving, and so should the odometer.

If you are using an oscilloscope and want to see the waves, make sure the red clip is hooked to the signal pin  #1 on the cluster, and the black wire on the ground pin #2. You should see something like this

And if you made the correct connections you should see this:

 

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