Fuse keeps blowing · short to ground
How to find a short circuit in a car
A fuse that blows the moment you put it in means a wire after it touches ground. A fuse that blows only sometimes means a wire that touches only when the car moves. Here is how to find either — without replacing fuses one after another.
Open the editor · ▶ Run the live demo
Step by step
- Find what the fuse feeds: the fuse box lid or the wiring diagram lists every load on it.
- Unplug the loads on that circuit; if the fuse now holds, the fault is in a load, not the wiring.
- Put a test lamp (a 21 W bulb) in place of the fuse. While the short is there, the lamp lights at full brightness instead of the fuse blowing.
- Unplug connectors along the harness one by one: when the lamp goes out, the short is between that connector and the last one.
- Wiggle the harness at doors, hinges, the steering column and brackets: the lamp flickers when you touch the spot.
Why the test lamp works
The lamp limits the short circuit current to about 2 A, so nothing burns while you search, and its brightness shows you whether the short is still there. In WireForge you can try this: replace the fuse with a lamp and hold the short — the lamp lights instead of the fuse blowing.
Practise on the demo
- Open the “Short circuit and a fuse” demo and hold “Chafed wire” — the fuse blows.
- Open it in the editor (copy it to your account) and replace the fuse with a Lamp.
- Simulate and hold “Chafed wire” again: the lamp lights brightly instead.
- Disconnect wires one by one to see where the short disappears.
Questions
Why does my fuse keep blowing?
Either a wire after the fuse touches ground (a short), or the load draws more than the fuse rating (an overload, e.g. a seized motor). A fuse that blows instantly is almost always a short.
Can I put a bigger fuse in?
Never. The fuse protects the wire; a bigger one lets the wire overheat and burn before it blows.
Where do car wires usually short?
Where they move or touch metal: door and tailgate hinges, under seats, at the steering column, on sharp bracket edges and near the exhaust.
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