I should know this the answer. I probably used to know this, but after being retired for 7 years, you forget some things ! This is automotive related but it is really a general electronics question.
Auto tech is diagnosing a problem. He unplugs a solenoid and probes the 2 pins in the connector on the harness with a DMM. One pin is connected to Vbatt, the other (I assume) to the Drain of a MOSFET (I don't know if there is any additional back EMF protection outside of the MOSFET). There is no signal to the Gate. The DMM reads Vbatt.
Plug a 12v test light between Vbatt and MOSFET and nothing.
Now I know this is related to the difference in impedance of these 2 test devices (10MΩ vs about 50Ω), but I can't explain it !
Auto tech is diagnosing a problem. He unplugs a solenoid and probes the 2 pins in the connector on the harness with a DMM. One pin is connected to Vbatt, the other (I assume) to the Drain of a MOSFET (I don't know if there is any additional back EMF protection outside of the MOSFET). There is no signal to the Gate. The DMM reads Vbatt.
Plug a 12v test light between Vbatt and MOSFET and nothing.
Now I know this is related to the difference in impedance of these 2 test devices (10MΩ vs about 50Ω), but I can't explain it !