DC Non-contact voltage detector

Serf Life

Serf Life

Been here much more than a while
Location
Maine Island
Looking for a test pen gizmo for truck/trailer wiring if one exists. My normal one doesn't register hot wires in the truck and have had a spell of running lights, brakes etc issues a detector would ease tracking down.

For those who don't have a proximity tester, get one as they are cheap and sometimes the client doesn't know if the exposed Romex line going to their light screwed to the tree is actually hot!
 
The emf/magnetism field picked up by ac non-contact detectors is picked up because its existence caused by it's nature of changing with time. Dc can separate a charge like static electricity but that's a whole different animal electrically speaking. For 12V dc first line of attack is high impedance sensitive multimeter. If that gives you hope then off the shelf led trailer testers can help further, but the real test is V supply under bulb load drawing current which relies on good source, good wire and good path to ground - all of which can knacker you. I wired an 1156 to a trailer connector where I can hook the bulb to each terminal in turn (proves vehicle side ok). A proxy is an old fashioned incandescent test light probe but it won't test to full current loading. If vehicle ok then track down trailer wiring one bulb at a time, starting with ground wire (often common so it can affect multiple bulbs)

Partially failed wires connections or corrosion are the usual culprits - or burnt bulb! eg partial failure may get you 7 v to the bulb under load but otherwise appear to test ok = some V present
 
@Bart_ I read through that a few times as my electrical literacy is lacking, and understood most(?) of it. Doing a search for using high impedance sensitive multimeter as proximity sensor didn't turn up much. I have a multimeter for batteries/alternators/ag-fence controllers etc, but as I understood them the contacts have to touch wire to register. Though I get that Dc"is a whole different animal" I rarely comprehend the applicable differences for my lay person existence.

Example of past dilemmas: power good at brake controller and fuses but not at trailer end and wires look good at rear junctions. Without any plugs inbetween to pop open and test, one is left to physically trace each wire and unwrap past splices/repairs. I appreciate the input and dumbing it down too.
 
Welcome to the pita world of electrical debugging:)

Ac vs dc - ac current flow makes electric/magnetic fields that induce voltage/current in nearby wires - a non-contact sensor is a "wire" exposed to said field and wire is connected to a regular high impedance multimter like circuit. It's the changing that makes it pick-up-able.

A normal voltmeter reads voltage via contact. Impedance is how much current gets tapped out by the contact. Small current/high impedance disturbs what you're measuring the least. But with testing trailer wiring you need the wiring to be able to hold it 12v voltage when the lower impedance light bulb sucks its load current. Or else the bulb might not light up.

One method of tracing power down a wire is to poke the sharp needle end of a test light through the wires insulation working from the last known good location outwards towards the load. If power gets to the bulb and it still doesn't light up that's when you provide a know-good ground to prove out if the existing ground has poor continuity ie extra resistance preventing good current flow.

I'm a believer in running explicit ground wires and not relying on a rusty corroded frame to be ground. If a light barely works you can measure dc voltage at the bulb ground pin - if its a volt or 3, there's undesired resistance in the ground path, most likely corrosion. If its basicly 12v then the ground path is an open circuit.(broken)

Solder all connections, don't use those little insulation slicing clips , twisting wires together or marettes.
 
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