Automotive Fuses can be tested using testlights. The testlight is an electrical testing device that lights up a bulb when current flows through it in a complete circle, this means that the testlight has two ends; one must be connected to the positive terminal (live) and the other must be connected to the negative terminal (ground/earth) in order for current to flow through it and turn up the bulb.
The testlight is a device that is used to check or test the presence of electric voltage or current, unlike the multimeter it does not show us the amount of current or voltage present in the tested circuit or component. The degree of the brightness of the light from the bulb in the testlight we can have an idea of the voltage present in that electrical system.
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The testlight is used to test the presence of electric power in a battery by connecting one end to the positive terminal of the battery (live) and the other end to the negative terminal (ground) of the battery. The testlight usually has two ends; one is usually a pin-like testing end and the other end could be an alligator clip, a pin-like end or some other design.
The testlight is used to test the present of voltage or current in automotive fuses, cables, connectors and other components in the electric circuit by placing one end (that is the end which usually has the alligator clip) on the negative terminal/ground of the power source (which is usually the negative terminal of the battery) and the other pin-like ending is use to touch and press on the two terminals of the fuses.
When the fuse is good the bulb in the testlight should light up when it is press against both terminals of the fuse, this shows that current flows through the fuse and that the connection within the fuse is still in good condition without any breakage or short circuit.
When only one end or terminal of the fuse lights up when the testlight is pressed on both terminals, this shows that the fuse is bad, it has a breakage in its conductor or an open circuit; as power can only be detected one side of the fuse which is the supply side but it cannot be detected on the other side due to the breakage or open circuit
When the level of brightness of the bulb in the test lamp is low during testing of the fuses it could be that the voltage of the battery is low or the fuse is corroded thereby having a degree of resistance to the flow of electric power.
When there is the two ends or terminals of the fuse is tested and there is no power on both of them then it could be due to a lot of reasons which are;
Power has not been supplied to that circuit; for some fuses one have to turn on ignition so that power can flow through that circuit before power can flow through it so that one can test them. In some other cases one need to turn on the unit that powers the fuse before power can be detected there for testing e.g. the crank fuses can only be tested when the engine is running or cranking.
The fuse itself may be very bad especially in a case when the two lids are totally corroded or cover with dirt in which the testlight cannot detect the presence of electric voltage or current even when the lid is pressed hard to the two terminals o the fuse.
The fuse circuit or the fuse box circuit could also be bad, as a bad fuse box circuit would not allow the flow of electric current through it. Therefore electric power or voltage would not be detected in that fuse.
The testlight could be faulty, a faulty testlight would not light up its bulb even if power is in that circuit, therefore before undergoing any test on the fuse box using the test light, it should be first tested on the battery to show if the testlight is working. Also during testing the testlight could also disconnect or the bulb may be blown out, in such case the test lamp should be retested on the battery to ensure it is working properly.
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