The blower and connector are a little different on a 140 , but the test should be about the same .
The basics to these type systems are the control panel sends a variable low voltage sig down to the regulator . This is called a trigger signal cuz it varies the conductivity of the regulator power transistor, The transistor/regulator does the heavy work so this high amperage does not have to go through the panel.
So, first test on these type circuits is to see if the CP is putting out a variable, low voltage sig. If it is putting out a sig but not variable with different settings, than you do not have but one speed . If it does vary the sig, then the regulator should vary the power to the blower . The reg just mirrors the degree of input of this trigger signal, so you can see why this is an important test for regulator diagnosis.
The reg is also a switched ground [ meaning there is always power to the blower at the pos/red terminal,] but the blue wire has to go through the reg to reach ground, thus completing the blower circuit. So, grounding the blu wire at the blower takes the reg out of the circuit and you get high fan, but that test also takes the trigger sig out too. So how would one really know if the reg was bad without checking for control panel variable low volts trigger first??
So, this is just a test that is done before condemning reg as bad , even though most of the time they are..
Trigger wire is usually yellow....