Help needed: Dim headlight issue

[D-Run]

I have a 1980 xs400 and i've been trying to figure out this electrical gremlin that is causing my headlight to be rather dim. Has anyone else ran into this issue? does anyone know any possible solutions?

Also, the headlight comes on as soon as I turn the key to the on position. From what i've been told that this should be the case. The headlight should come on after the bike has started. What is correct?

The headlight relay white connector looks like it has gotten little hot in the past. I'm wondering if the Blue wire leading to the hi-lo switch has been crossed with the red/yellow wire that comes from the fuze box.

Note:
I had to install a new diode on the white wire that leads to the headlight relay, but currently have it unplug because it was causing the charging voltage to drop a bit.

 

[Jeff0133]

Mine comes on at the on position, I think it it supposed to be that way.

 

[arfstrom]

With these bikes being 30 plus years old, it quite possible that your PO had made changes.

Stock operation is that the head light will not turn on,thus saving battery strength for starting the engine. that is done by a relay found under the battery. That relay is looking for power from the stator which flips the switch in the relay to allow power to the head light. Once the stator spins that is enough to turn on the light. (provided the diode is still intact) Diode is in the wire harness at the front of the seat, near where the tank meets the seat. I had when I was first troubleshooting swapped both relays and that was able to confirm to me that my headlight was fine. Then I put it back. That relay is no longer available, luckily its not usually shot. With that said, some PO's may have swapped it out, just cause they found something that might work.

There is a colored scan of a wire diagram in that folder,
http://www.xs400.com/threads/no-power-to-headlight-cant-trace-problem.7441/#post-77540

Okay, once you look at this, you start at the stator, it is a 3 phase stator. (3 wires = 3 phases. the white wires go up, and one splits to the diode. BBS360 proved that its only sensing power from the stator. which disproves my assumption, and ruins your hypothesis of a voltage drop. perhaps the wrong relay will ground out that white line, causing a voltage drop.f

I am famous, okay, quite popular in stating that the wires from the stator go bad, and there fore if you find that, replace those wires via Drewpy re-wire from the TECH section.

That should help. follow the diagram, and see if you freshen up ground points, (next to battery)

 

[xschris]

80 model sohc bikes headlight relays are under the front part of the gas tank. The light should only come on with the motor started or a kick over of the motor by foot. Dim lights are low charging volts so check at the battery what you get at idle.

 

[D-Run]

so I was out looking at the relays (safety relay and headlight relay) and noticed that the model? number was the same (4H7-01) on both of them. I have a few extra relays laying around and one has a model? number of 3H5-60. I plugged that one in (3H5-60) and it has seemed to fix the problem. I never knew/suspected that a different relay could fit the plug but operate in an incorrect manner (i.e. headlight coming on when it shouldn't). Has anyone notice this before???

xschris-
I'll be checking the charging voltage at idle next.

Arfstorm-
I have actually read and followed Drewpy's directions for the re-wiring of the stator meticulously. I feel that the stator is in good working order. But i'll go back and double check to make sure.

 

[xschris]

If your bike had the two relays that are by the battery and carbs you have an 81 model bike. Yes the wrong relay will cause an issue. The 3H5 is headlight and the 4H7 is e-start.

 

[arfstrom]

Cool, glad you got it figured out, the biggest sign for fried wires, is wires that sound like rice crispies, where the stator wires run up to the seat from the bottom of the engine.
Tobie

 

[MerlinDudley]

I have a 1980 xs400 and i've been trying to figure out this electrical gremlin that is causing my headlight to be rather dim. Has anyone else ran into this issue? does anyone know any possible solutions?

Also, the headlight comes on as soon as I turn the key to the on position. From what i've been told that this should be the case. The headlight should come on after the bike has started. What is correct?

The headlight relay white connector looks like it has gotten little hot in the past. I'm wondering if the Blue wire leading to the hi-lo switch has been crossed with the red/yellow wire that comes from the fuze box.

Note:
I had to install a new diode on the white wire that leads to the headlight relay, but currently have it unplug because it was causing the charging voltage to drop a bit.

On my 82 Maxim, the headlight is supposed to come on, when the ignition is on. When the starter button is pressed, the headlight is temporary disabled,(goes out) and comes back on when the button is released! This is the normal operation, in the ignition system. As to the problem of the dim headlight. Have a look at the bulb, and check the ratings on it, you could try up grading the bulb, for a brighter headlight? Before that, I'd check the wiring, to the headlight, for dirty contact's, or contact's that may have come a bit loose? After all these are 35+ year old bikes!

Merlin

 

[Wolfe_11B]

Run power to headlight with a new wire straight from a lamp relay via B+. Be amazed at how bright your headlight is.

 

[Jeff0133]

On my 82 Maxim, the headlight is supposed to come on, when the ignition is on. When the starter button is pressed, the headlight is temporary disabled,(goes out) and comes back on when the button is released! This is the normal operation, in the ignition system. As to the problem of the dim headlight. Have a look at the bulb, and check the ratings on it, you could try up grading the bulb, for a brighter headlight? Before that, I'd check the wiring, to the headlight, for dirty contact's, or contact's that may have come a bit loose? After all these are 35+ year old bikes!

....mine works the same....