Micro Trainer Faults
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A browser-based simulator that puts the same faults into a live circuit: an open, a high-resistance connection, or a short to ground, one fault at a time. Move the meter leads around and watch the readings change together.

It runs on any device with a browser. There is also a download button on that page that saves the whole thing as a single file, so it keeps working on a classroom machine with no internet connection.

Run it before anyone picks up a meter. It is the fastest way to see what each fault should look like before going hunting for one.

Every fault on this board belongs to one of four families. Telling them apart from the meter alone is the whole exercise.

• Open circuit. The wire is broken. No current flows, so the lamp is dead and there is no voltage drop across it. Measure along the circuit and you find full voltage on the supply side of the break and nothing on the other. The break is where the voltage disappears.
• Short to ground. The wire touches ground where it should not. Current takes the shortcut, the protection device opens, and everything downstream goes dead — including circuits that are not faulty. The giveaway is that more than one thing stopped working at once.
• Short to power. The wire picks up voltage from somewhere it should not. This is the sneaky one: the symptom is usually that something still works when it should be off. You cannot find it by looking for a dead circuit, because the circuit is not dead.
• High resistance. Still connected, but badly — corrosion, a loose terminal, a damaged strand. Current still flows, so the lamp still lights, just dimmer. The hardest fault to find and the most common one in the field, because nothing is obviously broken. You find it by measuring the voltage drop across the suspect section and noticing it is larger than it should be.

Four identical circuits. Left Front, Right Front, Left Rear and Right Rear. Each is a green lamp fed through a resistor, and with no fault set all four behave alike. That matters: the three healthy circuits are the known-good reference for whatever the fourth one is doing.

Battery. One CR2032, lifted to 5 V by a boost converter, so every measurement is on a 5 V system. Switch MASTER off when you are done — the cell is small, and a short left switched on will flatten it.

Test points. Each circuit has a test point on the supply side of the lamp, one on the ground side, and one at the ground connection. Put the black lead on a ground test point and walk the red lead along the circuit. The fault announces itself as the place the voltage changes when it should not.

The jumpers. The ten two-pin jumpers are break-in points. Pull one and you have made your own open circuit, anywhere you like, without touching a fault switch. They are also how you put a meter in series to read current.

Everything you measure is printed on the back. The four fault types with their symptoms, and the circuit identification scheme described below. Students should not need a handout to use this board.

The silkscreen carries a full wire-code scheme, the way a service manual does. Every length of wire between two break-in points has its own ID, so a fault has one correct answer and a student can be asked to write it down.

The feed side runs A1 from the battery to the fuse, F1 from the fuse to the switch, then L1 onward through the lighting circuits. The ground side runs Z1 through Z8, two per circuit. C1 to C10 mark the connectors and S1 and S2 mark the two splices where the feed divides.

So instead of “the left rear one is broken,” the answer is “L10 is shorted to V+” or “high resistance in Z1” — which is how the fault would be written up on a real vehicle. Set a fault without saying which switch you moved, and the exercise is to name the section.

Short a circuit to ground on a vehicle and the fuse blows. This board does the same job with an electronic fuse instead of a glass one: it limits the current in microseconds, lights the red indicator, and recovers — so a class can short the same circuit a hundred times without consuming anything.

That is worth understanding in its own right, because electronic fuses are now in the vehicles your students will work on. There is an interactive animation of what happens inside one, and a short video walking through it on the real board.

Watch the short video

Every board is tested before it ships. If one arrived damaged or fails in normal classroom use, email me and I will make it right.

Include your order number and a photo of the board if you can, which usually gets it sorted in one reply.

Email: scott@sbctrainingllc.com

Thank you for supporting a small shop. This board exists because students were being asked to find a fault before anyone had shown them what each kind of fault actually does to a meter reading.

I build trainers and curriculum for other systems too, including series and parallel circuits, relays, lead acid batteries, and CAN bus. If your program needs something that does not exist yet, tell me what you are trying to teach and I will tell you honestly whether I can build it.