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It would connect the ground side of the idiot (alternator) lamp. In your case its just an extra wire.

Clusters with voltmeter do not use the brown/tan (88 Elect Manual call it as tan w/tr) wire. Yellow wire is hot with KEY ON and during CRANK.

Your scanner is reading digital data and is correct. Engine is running very lean (O2=4.98vdc) . Note INJ PW climbing to 8-9 mS prior to going into OPEN loop. Check fuel pressure.

Its free: 88 Electrical Manual

See if this helps. Should be close if not exact. 88 Electrical Manual

Disconnect vacuum source to HVAC unit. Default (no vacuum) is defrost only.

The 2.5L uses 5 fusible links, while the 4.0L uses 7. Not sure how one would 'work around' that. 88 Electrical Manual

Tie the two feed wires (1157 socket) together for better contact with the bulb (1156). Backyard engineering at its best.

No, just keep in mind the length of the O2 wires when determining bung location.

Think about adding OEM oxygen sensor to your list. How many mile/km is on the vehicle?

Michelin Defender Highway Tire

Idle Air Control (IAC) will also kick up when automatic transmission is engaged, with no noticeable change in rpms due to load.

Thats what the microprocessor (ECU) does with any and all inputs, it control the outputs.

True that engine idle will increase when AC in engaged, but with the AC load now on the engine, idle rpms will remain the same, that is, not drop in rpms with the load. Yes, ECU controls Air Stepper Motor (idle air control motor, etc whatever one calls it) using AC Select and AC Request inputs to the ECU. This will kick the idle air motor 50 steps (≈50 rpms) when AC is engaged.

Thanks for the follow up. I'll need to remember this one. So the Torque Converter locks up properly on acceleration and disengages when brakes are being applied? Cruiser scores one point, lesson learned.

Take the two wires off at the porcelain thingy (fuel pump ballast resistor) and connect them together. Try restarting the vehicle.

AC is not required for Radiator Fan to work, but you do need a radiator temperature switch (closes at 190°), controlling a radiator fan relay (coil side). There is also a Fan Diode Assembly, but for now this one can wait.

How did you check pressure at fuel pump? A check valve in the fuel pump outlet maintains and holds system pressure along with the fuel pump regulator.

If you "T" in between the fuel filter and fuel pump with 40+psi on the gauge, while only reading 18-20 psi under the hood at the schrader valve, maybe your dropping pressure across the fuel filter.

Yes, check CPS. Voltage measurement is taken using the AC scale of your DVM. Check Cruiser's Tip on checking and moving CPS closer for better action. RENIX CPS TESTING AND ADJUSTING

Scanner and maybe the ECM seem to be floating (no ground). Check for continuity between Diagnostic Connectors and the battery negative. D1-3 (G105) and B- D2-7 (G104) and B- Has this vehicle ever run properly?

Engine??? Trans???

Welcome. If you plan on keeping your nice looking MJ for a long time, you'll need to make this guy your friend. Cruiser tips

Tail/Turn/Brake lamps are dual filament bulbs. Turn/Brake are one filament, while Tail is the other. Check the filaments. Also check for voltage with the bulb removed. Need to be careful here since bulb is case grounded. Gauge cluster lamps are controlled by the dimmer switch. Give it a twist. Make sure that not your problem.

I hate typos, especially mine.