electrical testing

[marinabrid]

Hi all
Im sure someone can answer this,
if i test a 12v supply and power is there, how do you test if its coming out the other end where the earth is ?
with my probably incorrect thinking, if 12v is going in and getting used by the thing its powering   why then does 12v not come out of the end where its earthed ?
or is there a way to test that the circuit is complete.  would it be the same as continuity testing ? one probe on one end and one on the other and hope the meter beeps.
Thanks very much.

[Mirez]

You don't really test like that.... you want 12V on one side and ground on the other.

Attach the black probe to a known good ground.
Then ue the meter in DC mode and apply the red prove to the live, you should have 12V with a healthy supply.
Next use the meter in resistance mode and with the circuit disconnected. Apply the red probe to circuits ground wire and check the reading is on (or very near to) 0.
That proves you have a good supply and a good ground which is all you need to diagnose the circuit, if it still isn't working then the component in the middle is faulty

If you want to test whats going through that component then you need to connect the meter in-line with the circuit (in series) and use the current mode to measure what's being drawn. That's normally a pain because you have to either chop into the circuit or find a 'break-in' point such as the earth eye. If the circuit is substantial enough (such as a heated screen) then you may be able to use a clamp on meter instead but that's another topic!