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Honda B18 Alternator wiring with PMU-24 install

PDM Installation & Configuration

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I'm installing a ECU Master PMU-24 and ADU-7 dash into my Honda Civic with B18C engine and OEM ECU.

I'm working out the final details of the wiring and have some questions regarding the alternator wiring. You van find the schematic in attached picture.

The alternator has a 4-pin connector on it with pins labeled:

1: "C" - connects to ECU

2: "FR" - connects to ECU

3: "IG" - connects to 12V power supply

4: "L" - connects to battery light in OEM dash.

At the left top of the schematic you can see that the OEM fuse/relay box contains a "Electronic Load Detector (ELD)" (1) it has an output pin going to a input on the OEM ECU (2).

As far as I have understood the ELD measures the current consumption and based on that it changes the voltage (0-5V) on the output going to the ECU. Which in turn adjust it's output going to the alternator.

I mainly have two topics.

1: What do I do with the wire going to the OEM battery light? Can I leave this disconnected or do I need to wire in a resistor? (I plan to generate a "light" on the ADU dash based on that from the PMU.)

2: Since the fuse/relay box is going, the ELD is too. So what do I do with the input on the ECU? Do I even need it?

I guess I could us the analog output of the ADU dash to mimic the signal from the ELD to the ECU. Bu then I would need to know which current corresponds to which voltage on the output of the ELD. But this seems over complicated since I plan to switch to an standalone ECU in the future.

I've also read somewhere on this forum in a topic regarding a Honda K20 engine you could leave all pins on the alternator disconnected except for the 12V pwr supply...does the same apply for the B-series engine? Or would this result in a fault code on the ECU? Or potentially damage the Alternator and/or ECU?

Any tips/experience and advice is welcome!

Thank you.

Attached Files


All typical OBD1 Honda ECU tuning options I've seen have the ability to toggle off ELD errors, and then you don't use those circuits.

The bulb isn't elegant, but hiding it somewhere is the lowest effort option to keep the alternator charging. That said, hopefully someone will have a more elegant solution they know works in your application. I've never seen testing the resistance of the bulb by itself and using a resistor of that same resistance cause the alternator to charge, so I don't suggest that. Resistor selection will need to be done carefully to both get the alternator to charge and avoid starting the resistor on fire.

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