I've been diagnosing a problem with a relay on my car. One of the pins in the socket that the relay goes into controls the ground for the throw of the relay. When the car's computer wants the relay closed, ground is available on that pin. When the car's computer doesn't want the relay on, ground is not available.
I want to see if ground is available on that pin.
My understanding is that the best way to do this would be to measure continuity or resistance between the ground pin in the relay socket and the ground terminal on the battery. Continuity (or a low ohm reading) would indicate that the circuit is closed. Unfortunately, the computer only turns the relay on briefly, and my multi-meter is slow, so I never have a chance to see if this happens. (If I touch the multi-meter leads together, it takes 5 or 6 seconds to get a solid 0 ohm reading... and I have about 2 to work with.)
The meter will measure voltage much more quickly. If I put the red lead of the meter on the ground pin for the relay socket, and the black lead on battery ground, I get no reading (really small fluctuating values, as if I had the probes in the air) most of the time. However, when the relay is supposed to be activated, I suddenly get a 5v reading. The positive side of the throw is usually 12v when measured against the ground terminal of the battery, so there's a difference of 7v.
Is this an indication that this pin is being correctly connected to ground? If so, why? I have some basic electrical understanding, but I'm not an EE by any stretch of the imagination...