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Harry Bloomfield Harry Bloomfield is offline
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Default Testing H4 car bulb with multimeter

Stan pretended :
Using a multimeter, what resistances would I expect to get from a
working H4 car headlight bulb?


Thank you for any info.


Usually you can check them without a meter - just give the lamp a sharp
tap with your finger tip and see if the filament vibrates excessively,
as if broken.

If you really want to test it...

One of the three pins is common - connected to both filaments, the
other two are the main and dip beam connections. With a multimeter and
assuming the lamp is good, you should get a value of a few ohms between
any two pins. The two pins which have the higher value between them,
means that the third pin is the common.

With care you could test the lamp across a 12v battery. Similar to
above, the two pins which produce the dimmest light out, means that the
third unconnected pin is the common.

--

Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk