Car wont start unless door is open

I use both lamps and meter, and more. Meter, common 12V bulb test lamp, LED test lamp as well as "large bulb" test lamps. One is an old headlamp, draws LOTS of current. If you are searching fuse-blowin' dangerous harness meltin' short, you can put that big lamp in series with the battery ground cable, and all that will happen if the short becomes activated---is that the lamp will light

I also have an old tail / stop light socket with an 1157. This is handy for LOTS of stuff because you can configure it to draw different amounts of current..............

1......leave the shell unconnected, connect the test to the two wires. This puts the filaments in series, lowest current configuration
2....Connect test to shell and tail lamp filament, a little more current draw

3....Connect test to shell and stop lamp filament, larger current draw

4...Connect test to shell, and to both tail and stop wires twisted together, maximum draw

This can also help find shorts, as well as loading circuits like a suspect switch or fuse holder to see if there are poor connections.

And learn to "wiggle test" stuff. Very important. Loose connectors, terminals, etc.

I agree with Mattox learn to test under load to show up poor connections. I rarely use an ohmeter on automotive. Usually, that's the last mode I use.

Be aware (especially with AC line power) that modern digital meters can lead you down the wrong path. This is because they take SO little current to operate. For example, you can stick one probe into the hot side of an outlet, and simply grab the other probe with your finger. Your body will act like an antenna, and you will read a fairly high voltage.