Electronic Ign. Control Unit (ECU) Heat condition

Mattax said

Here's a catch, in run position the ignition and alternator are turned on. In other words they draw power when the key is in run. This is important to know. Any time the power is flowing out of the battery, its voltage will drop.

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Using orange arrows to indicate current flow with key switch in RUN, engine off.


All power comes from battery. Voltage does not drop until it reaches a device with resistance. As current passes through those devices, voltage drops.

With the engine running, alternator provides the power. But in terms of voltage, same deal.
In an ideal world, if the alternator output is at 14.1 Volts, then everything up to the devices will be at 14.1 Volts.