[85lebaront2]

Does anyone on here have any expertise on the 80s vintage electronic dash units. Maybe someone with any type of schematic? I have a bunch I bought cheap from someone who wanted them gone and I know the 5 4312654 ones (1984-87 G body) all need the push button switches replaced. The other 5 are the full vacuum fluorescent ones (4312851) from 1988-89 G bodies and 1987-89 J bodies all display FAIL 2 in the initial test.

Further diagnosis points to it being the gas gauge circuitry as grounding the #21 pin (natural connector) gives no response from the gauge (it still shows empty). Oil pressure gauge will go full scale with this. Oil pressure (pin #5 (black connector) shows 9 VDC open circuit, gas gauge pin shows 5 VDC open circuit. I didn't check the temperature gauge circuit (pin # 9 black connector).

I would like to get the mating plugs if someone has some old harnesses they are cutting up for parts. they are 13 pin black and natural colored plugs. I could also use a 21 pin black and another 13 pin blue as that is what the older electronic clusters used along with a green 7 pin for the pull up resistors (same as the radio plug).

 

[ImperialCrown]

I have replaced 'leaky' electrolytic caps on these. While not a direct short, gradually they increase current over time that can damage regulators and transformers. Many times a visual and/or smell inspection will reveal burnt components with residue marks on the circuit board.
Voltage regulators can be replaced with generic 5 and 8 volt components.
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Transformers are harder to find. The VF tubes run at a 'stepped-up' 22 volts from the 12 volt supply.
The 'tact' switches, like the radio pushbutton switches of the era were prone to failure. They lost the 'click' feel and could intermittently close the contacts. These are available generically as well.
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Yes, many of the electronic clusters, Travellers, OTIS/EVIC, as well as Infinity audio components are probably still serviceable.

 

[85lebaront2]

I have already rebuilt a pair of the 4312654 1984-86 G body ones, switches on one were completely shot. Bigger issue on those was the tachometer LEDs, many bad solder joints. They would actually "PASS" the test sequence, but have either no tachometer response or gaps in the response.

 

[ImperialCrown]

The LEDs and VF tubes themselves usually stay good, the solder joints fracture over time with heat fluctuations and vibration. Cold or broken solder joints are easily reflowed to make a good joint.

 

[85lebaront2]

That is what I have found so far. I would love to find some schematics on these so I would know where to look for the problems. So far, none of the later boards have obvious failed components. Since the rear board (seems to be power supply and the integration for the gauges) is a double sided one it makes it interesting to try to follow the path taken by the fuel gauge signal.