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Do you recall if the HI BEAM indicator was lit (IP Cluster)?

I think what you just posted explains why Headlight Switch C269_1 melted. I believe your shorted between HI BEAM circuit and Instrument Panel Lamps.

Need to make sure you can't dim your HI BEAM's with the dimmer switch. Also check and see if the dimmer dims the Instrument Panel Lamps.

Instrument Panel Lamps are more than likely finding the proper grounds. My question now is the voltage sources. 1) Panel Lamps that work with HI BEAM, yet shows no dimmer control, means HI BEAM circuit is shorted to Panel Lamps between Headlight Switch and Panel Lamps. 2) Headlight Switch C269_I (melted terminal) could be the cause for no Panel Lamps, but what caused the high current to melt it. Don't think that the terminal (C269_I) is the one that melts with high current flow thru Headlight Switch. Seems compound problems here, HI BEAM short to Panel Lamps, No voltage thru Headlight Switch (dimmer circuit) for Panel Lamps. Need to trace the HI BEAM circuit for short to Panel Lamps. Should solve this one first.

This question is more out of curiosity. When HI BEAM's are ON, using the dimmer switch, can you dim all the Instrument Panel Lamps?

Your melted terminal on the Headlamp Switch (C269) is C269_I. C269_I feeds Instrument Cluster lamps and other lamps used on the dash. Do the other lamps work normally (ex: ash tray lamp, fog lamp switch lamp, PRNDL lamp, heater/AC panel lamp etc etc)? Don't understand why they work on HI BEAM.

Page 78 shows C203 pinout. 88 Electrical Manual

IP Cluster uses two (2) pins for grounding Illumination Lamps (C203). Check both C203_5 and C203_10 for path to ground from the connector.

88 Electrical Manual

That's exactly what STFT/LTFT is all about. RENIX seems to be working just fine and as intended. Good thing you got that MT2500.

Numbers well within the O2S range of authority.

How's your 3rd O2S doing?

Looks good, very clean. Wonder how white would've looked like.

Start with battery, battery terminals, battery cables and then all the grounds.

Your signature doesn't say what engine. I'll take it as a 4.0L by your fuel pressure posted above.

Single wire, single bullet connector is cruise control ground. The other four (4) wires are engine block grounds.

That one photo with the cracks on the bottom, if that a bubble it could have been cause by excess of heat and it look like something blew up inside.

I think that tap was used for ICM production, certain types of Tachometer could be connected there.

C103 is a inline connector (Engine harness to Engine Control harness) and C103_B (RED) goes to fuse link G.

If CPS is assumed good, the injector within the throttle body should spray fuel. Does it? Two pin (C214_A) should be empty. C214_B goes to the ECU for timing control.

Ignition module only has two connectors. One is a 3 pin and the other is a 2 pin. Loss of spark can be caused by a faulty Crank Position Sensor (CPS).

Welcome to CC. This 88 manual could help with most of your questions. 88 Electrical Manual

Check secondary ignition for possible crossfire or carbon tracking under distributor cap.

Could be leaky injector(s). Check fuel pressure. Gauge should hold pressure after cycling KEY ON, then KEY OFF.