Having trouble with my trailer lights.
I have a converter going to a 4 pin flat connector. When I use my multi-meter on the car-side harness, it shows voltage at all the connections, brakes, signals, running lights. But when I attach my circuit tester clip to the white ground connector (same connection I used with the multi-meter, so I know the ground works), and the probe into the brown, green, and yellow plugs, nothing. The light doesn't go on. If I attach it to my battery it lights up fine, so I know it's working. What's going on? I want to use the circuit tester to check all the wires back to the trailer lights, which I can't do easily with the multi-meter.
Ed

 

Welcome to the forums.

99.9% of the time it's a ground problem or loss of ground.

Use an ohmmeter set to Rx1 to check for ground on the white wire.

 

Thanks! So it's possible that the voltmeter connected to the white ground and
any of the signal or taillight leads shows voltage, but that there still could be a ground problem? And that the circuit tester won't light up even though the voltmeter seems to show power?
I'll check with the ohm meter.
Ed

 

Your digital meter will read voltage with your hand connecting the ground lead to chassis. That's how sensitive they are.

I only use test lights for all trailer wiring. I have test lights with 30' of wire on them.

 

I bought a power probe several years back and don't grab anything else anymore. It will check for lower or ground or it will supply either at the operators request.

 

I may be misreading this, but it sounds like you are testing the trailer plugs when they are not connected to the car plug. If so, you need to switch your meter to the ohms reading to test continuity.