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Since you've lost your courtesy lamps, I think your dropping voltage at the fuse (Dome 10A), IP splice C or the wire in between. 88 Electrical Manual Dome lamp fuse/IP splice C: page 63 IP splice C location (C with a circle around it): page 91

Voltmeters can show good voltage, but they can't determine if current will flow (voltage drop). Can you test the red (12vdc) wire with a test lamp? This will show current (thru the test lamp) can flow to ground. G102. Bottom of dash, near the steering column, when in the ON position. When in the SW position, ground is provided by each door switch. Also when the headlamp switch is turned to ON will provide a path to ground.

Isn't something suppose to be in that groove on the caliper?

So both L/R courtesy lamps don't work either?

CW57, just curious here, is your brake warning switch connector just hanging there? If you jumper the connector or leave the BWS connected, you could at least get bulb check (BRAKE) during CRANK and your parking brakes to light the BRAKE bulb. This is no big deal here, only if your interested.

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Farewell my forum friend.

Try cleaning the starter relay ground (G104). Both G104 and G105 are located on the engine block. They pigtail out of the engine control harness near the rear of the engine block.

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Disconnecting the Brake Warning Switch also disconnects the Parking Brake Switch. You need to disconnect the Parking Brake Switch in order to determine which switch is faulty. Brake Warning Switch or Parking Brake Switch. There is also a third path to ground with the Ignition Switch (Bulb Check circuit).

With key ON and engine not running, power is only there for 2-3 seconds.

Did you remove the wire from the ballast to do this? If so, may be the EGR solenoid side and not the fuel pump side (the other one).

EGR valve solenoid. Powered by the same voltage that powers the fuel pump.

Click here for 88 ELECTRICAL MANUAL

O2 sensor does have a 'range of authority' over injector pulsewidth, but this is limited control. Once STFT and LTFT are pegged one way or the other, open loop becomes the default. Under extreme conditions (extra high fuel pressure, injectors too large/too small, air leaks) even open loop is no good.

Great article, good read.

I wonder if the two (2) styles of fuel rails (regulator w/vacuum and regulator wo/vacuum) are based on the type of fuel control systems used in fuel delivery. In other words, is it speed density vs mass air flow, for fuel control. I do know that speed density requires a constant fuel pressure (always 39psi) at the tip of the injector. This is achieved by varying fuel rail pressure as manifold vacuum varies. Between the two forces, pressure at the injector tip stays the same.

The first and last thing I'm going to say is "I don't know". Now with that in mind, I think you must maintain the fuel pressure regulator that senses manifold vacuum. Not sure if returnless regulators do that. Could depend on which ECU controller you use. Also, Mass Air Flow (MAF) sensor vs Manifold Absolute Pressure (MAP) sensor for fuel control may come into play here. Now remember the last thing I was going to say.

When you set the condition for pump running, try removing each fuse to determine if pump shut off. This may give a clue to where short to voltage is.

Not true, circuit is unprotected. Technically speaking, your yellow fused wire is undersized (wire gauge) and fuse protected. Both your wiring schematic and the 88 electrical manual show no fuse or fusible link between the battery positive terminal and the starter relay stud. Your schematic shows no wire gauge size, the 88 electrical manual calls for 8 gauge (AWG) wire. Adding this 8 gauge (AWG) wire would render your yellow fused wire useless. Yes this is consider to be a unprotected circuit.

Use this, should be the same for 89: 88 Electrical Manual

Power distribution has three (3) fusible links that are color coded green. One of these fusible links feed the Ignition Switch. If that's the one you replaced, suspect Ignition Switch.

So both the engine is running and the starter is engaged (cranking)?

Two questions, 1.) Do you have a temp gauge or idiot light in the cluster? 2.) Are your sending units for a temp gauge or idiot light?

Without having a fuel pressure gauge to determine if fuel psi is changing when vacuum is removed from the fuel pressure regulator at idle, try using MT2500. When engine is at idle and in closed loop remove vacuum source at FPR and see if INJ PW time decreases or/both if STFT starts to lower in numbers. Also closed throttle position is learned. Meaning you may have to give it some time to learn.