What an electrical load switch is
An alternator under heavy load is harder to turn, and at idle that extra drag can pull the RPM down or make it hunt. Many older factory charging systems include a signal that changes state when there's a significant electrical load on the system. The factory ECU used it to bump the idle up ahead of time.
The Nexus can do the same. Once the switch is configured, you can use it as an idle up condition so idle control adds airflow as soon as the load comes on, rather than waiting for RPM to drop and then correcting.
Newer cars usually manage this differently, through alternator control or the body computer, so this switch is mostly relevant on older platforms that have one.
Setting it up in NSP
The Electrical Load Switch node is where you assign the input. The signal is normally wired to either an AVI or an SPI, and any free one will do.
On an AVI (analog input)
An analog input reads voltage, so you tell it what counts as on and what counts as off. Measure the signal at the ECU with the load off and on, then set the on and off voltages with a clear gap between them so noise can't make the switch chatter.
On an SPI (digital input)
| Setting | Set to | Why |
|---|---|---|
| Sensor Type | Hall Effect (digital) | It's an on/off signal, not a pulse from a reluctor |
| Pull-up | Enabled | Gives the input a voltage to sit at when the signal is open |
| Edge Select | Falling if the signal grounds when load is present. Rising if it goes open circuit when load is present | Tells the ECU which transition means "load on" |
Checking it works
- With the engine idling, watch the switch state in NSP.
- Turn on a heavy load such as headlights, heater fan on high and the rear defroster together. The switch should change state.
- Turn everything off and confirm it changes back without flickering.
- Once it's reliable, add it as an idle up condition and tune the added airflow until the idle stays steady when loads switch on.
Troubleshooting
| Symptom | Usually |
|---|---|
| Switch reads on all the time | Edge set backward, or the pull-up is off |
| Switch flickers at idle | AVI on and off voltages too close together |
| Switch works but idle still dips | Idle up amount too small for the load |
Running an Elite instead? See the Elite electrical load switch article.
