What the input is for
The Electrical Load Switch is a simple on/off signal that tells the Elite when there's a significant electrical load on the car. When the alternator suddenly has to work harder, it takes torque from the engine. At cruise you'd never notice, but at idle that extra drag can pull RPM down or make it hunt. Giving the ECU a heads-up is typically used so idle strategy can prepare for the load instead of waiting for RPM to drop. See Idle Control for how idle responds to inputs like this.
The signal usually comes from the switch or relay for the load itself, such as the headlight circuit, a high-current fan relay or the rear demister. Many factory harnesses already have an electrical load wire that went to the original ECU.
Choosing the input
You can use either an SPI (synchronized pulsed input) or an AVI (analog voltage input). They're set up differently, because an SPI thinks in edges and an AVI thinks in voltages.
Setting it up on an SPI
| Setting | What it does | Our advice |
|---|---|---|
| Edge Select | Tells the ECU which direction of change means "switched on" | Falling if the switch grounds the wire when active, Rising if it feeds the wire voltage when active |
| Sensor Type | How the input reads the signal | Hall Effect for any switch input |
| Pullup | Holds the input at a voltage while the switch is open | On for a switch that only ever grounds the wire, otherwise the input floats when off |
A ground-switching signal is the most common. Pick Falling with the pullup on, and the input sits high until the load comes on and pulls it low.
Setting it up on an AVI
An AVI sees a continuous voltage, so you tell the ECU two thresholds: the Switch On Voltage and the Switch Off Voltage. The switch turns on when the voltage crosses the on threshold, and it only turns off again once the voltage crosses back past the off threshold.
The space between the two is deliberate. It's hysteresis, a dead band that stops the reading flickering on and off when the voltage wobbles because of alternator ripple, voltage drop or noise. Put each threshold comfortably inside the real on and off voltages, never right at them.
Worked examples
A switch that pulls the wire to ground
Say you measure about 4.8V at the input with the headlights off and about 0.2V with them on. The switch is on at low voltage, so set Switch On to around 1.5V and Switch Off to around 3.5V. The input reads on once the voltage drops under 1.5V and stays on until it climbs back past 3.5V. Anywhere in between, it holds whatever state it was already in.
A signal that goes high when active
Now say the input sits near 0V when the load is off and rises to about 5V when it's on. Flip the logic: Switch On around 3.5V and Switch Off around 1.5V. The switch turns on as the voltage rises through 3.5V and turns off once it falls below 1.5V.
Don't guess the voltages. With the input configured, watch the raw voltage in ESP while someone switches the load on and off, with the engine both running and off. Set your thresholds from what you actually see.
Troubleshooting
| Symptom | Usually |
|---|---|
| Always reads on (or always off) on an SPI | Wrong edge, or pullup off on a ground-switching signal |
| Flickers on and off | AVI thresholds too close together or too close to the real voltages |
| Never changes on an AVI | On and off thresholds reversed for the direction the signal moves |
| Idle still dips when lights come on | Input works, but the idle strategy isn't using it yet. Check your idle settings |
FAQ
Can I combine several loads on one input?
Yes, as long as each load's signal is isolated with a diode so they don't back-feed each other. The input only needs to know that something big is on.
Is this the same as alternator control?
No. Alternator Control sets how hard the alternator charges. The load switch only tells the ECU that a load is present.
