Ωhm

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.

Scanner only uses serial data from the microprocessor. If vehicle runs and operates OK, I don't know what to say. Not much help here.

Link off the internet The Peugeot BA10/5 transmission is a five-speed, overdriven, light-duty, passenger car transmission used by AMC Jeep from 1987 until mid-1989 in the YJ Wrangler, XJ Cherokee and MJ Commanche with the AMC 258 & 4.0L I6. The 10/5 transmission had a poor record for durability and service, and consequently had the distinction of being the transmission with the shortest production run in Jeep history. It was gradually replaced by the AX15 during the 1988 model year.

You mentioned before you had two PCM's (88&89). Did the scanner work OK before on both of them?

Since old switch bench tested bad (fails to make contact) and new switch bench tested good (makes contact), its more than likely your problem lies in the switch not having enough travel to make contact. Take that piece of Brand New Junk (BNJ) and tell them you want a newer one before looking into any tranny work.

If you still have the old switch, check its operation with a ohmmeter across the terminals, by pushing in on the ball. Could determine if switch (old or new) is at fault or is it something internal to the transmission.

Good work. Good find. Hope this ends your electrical nightmare.

Ask if you can move this Post to "MJ Tech: Modification and Repairs". This will put more eyes on the subject.

Control your add-on relay (coil side) by using the ORN wire from the fuel pump relay (FPR_87). Do not cut this wire, but instead "T" into it. This will allow your add-on relay to act, function as the factory FPR. That is, the external fuel pump will prime during KEY_ON for 2-3 seconds and remain ON during CRANK, then RUN. Yes, ORN/BLK must be a complete circuit, as mentioned above.

Where did you locate the add-on relay for the external fuel pump? Does this vehicle have a fuel pump ballast resistor? Ceramic block on the left front inner fender. Two single wires (ORN).

ACC circuit drops out (no voltage) during CRANK.

Don't forget the hole needed for the wiring.

Yeah, lets hope someone else will chime in, but as of now, that the way I see it.

Not if you pulled out all the relays, it doesn't.

Since we can't kill the fuel pump from under the hood and C157 kills the fuel pump, that leaves C100 (ENG to IP) (Bulkhead connector) left to check (separate). In other words, your short to voltage is between C157 and the battery. Put a voltmeter on the fuel pump wire (should read battery voltage) and trace the wire(s) back looking for wires touching each other. Best I can do sitting in my chair.

With C157 connected, is pump on or is pump off?

Disconnect C352 (single bullet connector) (ORN/BLK) located near the RH shock tower. Connect C157.

Disconnect C157 (IP to CAB). Flat 6 pin connector located above/around the Parking Brake. This will divide the circuit in two.

Disconnect the BAL connector (ORN/BLK) at the starter relay. Disconnect one of the two wires (both ORN/BLK) at the fuel pump ballast resistor. Does either one of these turn off the fuel pump?

What were the spark plugs gap set to? Not sure exactly what the specs calls for. Anyone?

Remember, we don't bounce like our grandchildren do, anymore.