Topic: CB400F with dim high beam idiot light

[sitz]

A bit about the bike. It’s a Yellow ‘77 that was garage kept and exercised by the previous owner for over 20 years. It’s got 5k miles on it and, while not showroom, it is (in my utterly biased and non-expert opinion) is a solid 95% bike.

The problem: the blue high beam dash light is so dim I can’t tell it’s on unless it’s pitch black out. I pulled the cover and it does light up the teeniest bit, but that’s all. Swapped the bulb with known good one and that one lit the same amount as the original.

Two questions:

• How bright should it be; about the same as the others or dimmer? Anyone have pictures of a 400F with the idiot light on so I have something to compare it to? I searched the web/YouTube and failed to turn up examples.
• If mine is not behaving normally/correctly, any  thoughts on likely a causes?

Thanks.

[newday777]

Yes dim is not good.
Is the bulb socket corroded?
Do a test with a ground jumper to the socket edge to see if you have a bad ground.
Next open up the headlight, unplug the headlight and set it aside safely. Then inspect the connections in the bucket. You may have to close the female side of the bullet connectors to get a full connection. They loosen over time.

[The Lone Builder]

Have you tried cleaning the inside of the lens?

[seanbarney41]

I have seen this a few times before, never really fixed it...just assumed was caused by dirty connection causing voltage drop somewhere in the circuit.  I would check associated bullet connectors first, since that is easiest, then the hi/low beam switch next.

[MauiK3]

Yamiya has little LED bulbs for them, they work well.
Check all connections.

[Quattrocilindri]

The high beam blue indicator lens is not the same as the oil, neutral and turn signal indicator. The light is more filtered for a reason; and the reason is, if you ride at night on open country roads with no traffic and your high beam is continuously on, a bright blue indicator would be very bothersome to your eyes.
Of course, if you have the high beam on in bright daytime, (like I do on my 350F) that blue indicator is hardly visible, especially if you wear sunglasses under your visor. But who cares about that, as long as you have a brighter, 50 watt high beam headlight vs. the 35 watt low beam.
On my old 400F in 1976, while I rode on those British dark roads at night, I was glad that that blue light was not distracting because of this feature.
So, I am 99% sure that there is nothing wrong with the "dim" blue indicator light; it is that way by design.
And, if you drive cars, you'll notice that the blue high beam indicator in the dash is also "dim". Same concept.