24V Circuit Tester for Trucks: Fault-Finding on HGVs and Trailers

Short answer: a 24V circuit tester for trucks needs three things — genuine 12V and 24V compatibility, enough lead to reach the back of a trailer, and a probe slim and safe enough to work around modern ECUs. Get those right and you can trace trailer light faults, dead earths and connector problems in minutes instead of walking the length of the vehicle with a heavy probe.

HGV technicians know the scenario: a trailer light throws a fault, the driver is waiting to run, and you are working along the chassis loom “holding a heavy probe until your arm aches”. The two things that slow that job down most are a tester that only really likes 12V, and a lead that runs out halfway down the trailer.

Why 24V compatibility actually matters

Plenty of cheap test lamps are built for 12V passenger work and behave unpredictably on 24V commercial circuits. On a mixed fleet you want one tool that handles both without a second thought. The PowerScan PS100 is rated for 12V and 24V DC systems, so the same probe works on the yard hatchback and the 24V lorry beside it — and there is no worry about “connecting it and frying the meter”.

Trailer lights and dead earths: the everyday jobs

Most commercial electrical faults come back to lighting and earths, and they get worse in a wet British winter.

Tracing a trailer light fault

Start at the susie/plug, then work back. A tester that shows voltage and polarity lets you confirm whether power is reaching the connector, the run, or the lamp itself. Because a bad earth mimics a dead feed, being able to switch to a continuity check on the earth path saves chasing the wrong wire.

Finding a high-resistance earth

Corroded earths are the classic intermittent fault. A continuity check to 200 kOhm confirms whether an earth strap is actually doing its job, rather than guessing from a flickering lamp. The PS100’s tone-and-display feedback means you can work under a chassis without staring at a meter the whole time.

Reach: why 6 metres changes the job

A short lead is the difference between one clip-on and a dozen. The PS100 ships with a 6-metre lead, so from a single connection you can reach a long way down a rigid or a drawbar without constantly repositioning. It will not span a full 18-metre artic in one go, but it covers the units and sections you are actually fault-finding at any one time far better than a 1.5-metre probe.

Protecting the ECU on modern trucks

Modern commercial vehicles are as ECU-dependent as cars. The PS100 includes a high-impedance mode intended for sensitive signal lines, which is the sensible choice on CAN and control circuits where you do not want to inject a load. For the deeper how-to on using this style of tool, see how to use a power probe, and if you also tow for leisure, our caravan 12V electrics guide covers the same connector logic on smaller rigs.

A 12V/24V circuit tester built for commercial work

The Autel PowerScan PS100 is rated for both 12V and 24V DC systems, making it a genuine 24V circuit tester for trucks as well as passenger cars. At 30 g it disappears into an overall pocket, yet it reads 0 to 65V and continuity to 200 kOhm on a TFT colour display, has an integrated LED work light for dark chassis work, and a 10A thermal-trip breaker for safer live testing. The 6-metre lead reaches down a trailer from one connection, a high-impedance mode protects sensitive ECU signal lines, and it is powered from the vehicle battery so it is always ready. It is GBP 133.91 inc. VAT with free next-day UK delivery, 30-day returns and a 12-month warranty plus UK support, rated 4.8 out of 5 from 300 reviews.

Frequently asked questions

Can the PowerScan PS100 be used on 24V lorries?

Yes. It is fully compatible with both 12V passenger cars and 24V commercial vehicles, which makes it suitable for HGV technicians working across a mixed fleet without swapping tools or risking the meter.

How long is the lead, and will it reach a trailer?

The standard lead is 6 metres, enough to reach the sections you are fault-finding on a rigid or drawbar from a single connection. It will not span a full articulated set in one go, but it covers far more than a typical 1.5-metre probe.

Is it safe to use around a truck ECU?

It includes a high-impedance mode intended for sensitive ECU and signal lines, so you can check circuits without injecting a load where that matters. Avoid high-voltage systems and hand deep control-module diagnostics to a specialist.

Does it need its own batteries on a cold morning?

No. The PS100 is powered directly from the vehicle's own battery, so there is nothing to charge before a roadside or yard call-out.