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Electrical gremlins!

939 Views 5 Replies 5 Participants Last post by  Dan89flstc
So yesterday morning, the low beam is not working, flip to high it works. So I think I'll work on it after I get home. Pull into the garage and notice the high beam isn't working either. Must be the bulb, I have spares, so I'll just replace the bulb.

Annndddd the new bulb doesn't work either, so I pull out the meter, high beam has 12v+, low has 10v+, at the plug. Obviously something is going on with the low, but why isn't the high side working?

I ended up connecting a jumper to the light, and the old bulb works. So what am I missing?

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Inspect the plug itself, I had one go and it did the same thing, high beams, low beam then no beam.
I`m guessing you are checking for voltage while the bulb is removed from the socket.

This can give you misleading results.

If something is causing high resistance upstream of the component, you will get normal voltage readings when the wire to the component is disconnected...

It may be a bad switch or connection.

The most reliable way to check the circuit is the voltage drop method.

Bulb installed in socket.

Voltmeter (-) probe to battery (-) post.

Switch low beam on, touch voltmeter (+) probe to low beam terminal and note the voltage.

Switch high beam on and touch (+) probe to high beam terminal, note the voltage.

Try to touch the probe to terminal on the headlight (not the connector terminal), if possible.
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Also check the ground wire for continuity.
Just had this problem on a friend's bike. Check the plug connections for tightness (and possible light corrosion). See if there is any sign of melting of th e plastic on the plug. You may solve the problem by replacing the plug assembly. I have fixed them with a pair of long nosed pliers making a tighter connection on the pins.
Also check the ground wire for continuity.
Ugh...I forgot to mention that...good catch:)

Should be the first thing checked, the checks I mentioned would not find a bad ground, because the meter is grounded during the test.
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