Motorcycle Forum banner
1 - 13 of 13 Posts

·
Registered
Joined
·
7 Posts
Discussion Starter · #1 ·
I have a 70 Honda CL350 and I have been trying to trouble shoot the tail light. The brake light functions work correctly but the tail light only comes on when the headlights are switched off at the handlebar switch with the key in position 1. The schematic shows the brown wire to the tail light coming directly from the ignition switch. When I unplug the headlight (white wire) in the bulb housing the tail light goes off even when the switch on the handlebars is off, when it normally works. The tail light should turn on when the headlights are on. The tail light comes on with the ignition switch in position 2.

Any thoughts?
 

·
Premium Member
Joined
·
5,765 Posts
If you don't have one, I suggest getting a shop manual with wiring diagrams; Honda is best, but there are others. Then, go through the wiring connections in the headlamp bucket, to make sure all the colors are connected properly, per the drawing. It sounds like you have a few mixed up in there.
 

·
Registered
Joined
·
7 Posts
Discussion Starter · #3 ·
If you don't have one, I suggest getting a shop manual with wiring diagrams; Honda is best, but there are others. Then, go through the wiring connections in the headlamp bucket, to make sure all the colors are connected properly, per the drawing. It sounds like you have a few mixed up in there.
Thanks, I have a wiring schematic and the wires in the headlamp bucket appear to be connected correctly. Everything is color coded. Still can't find the problem though.
 

·
Premium Member
Joined
·
5,765 Posts
OK, I have every reason to believe Honda wired the 350 the same as my 450, so here goes.

The key switch has four wires: BATT (red), IG (black), TL1 (brown/white), and TL2 (brown). With the key in position 2, BATT connects directly to TL2, lighting the tail lamp.
With the key in position 1, BATT connects to IG, and TL1 connects to TL2. The IG (black) wire powers the coils, probably through a run/stop switch, and also goes into the headlamp bucket, where it connects to the lighting dimmer switch. The lighting switch has three output wires: LB (white), HB (blue),, and TL (brown/white). When the switch is set to L or H, it sends IG power to L or H, and it also applies IG to TL, which goes through the headlamp bucket to the TL1 wire of the ignition switch, and on to the TL2 wire, lighting the tail lamp.

Check your diagram to confirm it functions the same. If not, can you post the wiring diagram, so I can review it?
 

·
Registered
Joined
·
7 Posts
Discussion Starter · #5 ·
OK, I have every reason to believe Honda wired the 350 the same as my 450, so here goes.

The key switch has four wires: BATT (red), IG (black), TL1 (brown/white), and TL2 (brown). With the key in position 2, BATT connects directly to TL2, lighting the tail lamp.
With the key in position 1, BATT connects to IG, and TL1 connects to TL2. The IG (black) wire powers the coils, probably through a run/stop switch, and also goes into the headlamp bucket, where it connects to the lighting dimmer switch. The lighting switch has three output wires: LB (white), HB (blue),, and TL (brown/white). When the switch is set to L or H, it sends IG power to L or H, and it also applies IG to TL, which goes through the headlamp bucket to the TL1 wire of the ignition switch, and on to the TL2 wire, lighting the tail lamp.

Check your diagram to confirm it functions the same. If not, can you post the wiring diagram, so I can review it?
Thanks again. That is the same wiring on the 350. That is why I am confused why the tail light comes on when the lighting dimmer switch is in the off position. There should not be any current from the IG (black) in that position. The tail light goes off when the switch is in the low or high beam setting. The tail tail light works properly when the ignition switch is in position 2.
 

·
Premium Member
Joined
·
5,765 Posts
So, you get the high and low beams with the switch in those positions, but the tail lamp is off, correct?

Power is passing through the headlamp to the tail lamp when the switch is off, which implies the switch has the wrong colors, or something else is tangled in the wires. At this point, I would unplug all four wires from the switch, and use an Ohmmeter to verify it is wired per the schematic. It could be a previous owner swapped out the switch with one that has the colors mixed up.
 

·
Registered
Joined
·
7 Posts
Discussion Starter · #8 ·
I removed the wires from the switch and I tested each lead for continuity with the switch in the various positions. Everything was wired correctly and there was continuity when switched in the low and high positions and no connection when switched off. All of the instrument lights work and the headlight is working.
However the tail light comes on when the light switch is off and it is off when the lights are on. Interestingly I found that when the light switch is in the off position the current to the tail light is 12 volts measured from the lead(brown wire) to the positive side of the battery. When the key is in position 2 on the ignition the light comes on as it should but the lead measures 12 volts to the negative side of the battery or ground as it should. When the switch is on either low or high there is current on the brown wire that measures 12 volts to the negative or ground as it should but the light light goes off.
I am confused, seriously....
 

·
Premium Member
Joined
·
5,765 Posts
Seems like a grounding problem at the tail lamp. The current is flowing 'backwards' through the tail lamp when the key is on, but the dimmer switch in off; I assume the meter lights are also on it this position, and the tail lamp is dimmer than with the key in the #2 position. Unless you have a LED bulb in the tail lamp, that is, in which case you wouldn't notice the difference, and the meter lights may not glow. So, something is putting 12V through the tail lamp, possibly because the ground is missing, and a brake light switch is leaking enough to light the bulb. I find it unlikely that 12V is applied to the ground at the bulb, but screwed up wiring could do it. If the ground is missing, and the key in position #2, power flows through the tail lamp, then through the brake lamp, and on to try to power everything the IG output of the key switch does, which will look like nearly a ground to the lamps; the brake lamp filament is so much bigger than the tail lamp, it won't glow much, if at all.

Take the lens off, and make sure the socket shell measures ~0 to the battery negative, and that it is clean enough to make a good connection to the bulb. Odds are the socket is oxidized, or the ground wire from the harness has a break in it, probably under the fender. Do the turn signals, work?

Also, check for Voltage at the brake switch outputs, to see if a switch is sticking on; often, the switch on the pedal needs cleaning around the shaft that is pulled by the pedal.
 

·
Registered
Joined
·
7 Posts
Discussion Starter · #10 ·
Seems like a grounding problem at the tail lamp. The current is flowing 'backwards' through the tail lamp when the key is on, but the dimmer switch in off; I assume the meter lights are also on it this position, and the tail lamp is dimmer than with the key in the #2 position. Unless you have a LED bulb in the tail lamp, that is, in which case you wouldn't notice the difference, and the meter lights may not glow. So, something is putting 12V through the tail lamp, possibly because the ground is missing, and a brake light switch is leaking enough to light the bulb. I find it unlikely that 12V is applied to the ground at the bulb, but screwed up wiring could do it. If the ground is missing, and the key in position #2, power flows through the tail lamp, then through the brake lamp, and on to try to power everything the IG output of the key switch does, which will look like nearly a ground to the lamps; the brake lamp filament is so much bigger than the tail lamp, it won't glow much, if at all.

Take the lens off, and make sure the socket shell measures ~0 to the battery negative, and that it is clean enough to make a good connection to the bulb. Odds are the socket is oxidized, or the ground wire from the harness has a break in it, probably under the fender. Do the turn signals, work?

Also, check for Voltage at the brake switch outputs, to see if a switch is sticking on; often, the switch on the pedal needs cleaning around the shaft that is pulled by the pedal.
Again, very good information thanks. Both turn signals work. I will test the socket shell when I get a chance. Part of the confusion comes from the fact that all of the other circuits that are connected to brown/white wire such as the instrument lights work properly. It is also interesting that the tail light goes off when I unplug either the white headlight wire or the green from the headlight.
 

·
Premium Member
Joined
·
5,765 Posts
Interestingly I found that when the light switch is in the off position the current to the tail light is 12 volts measured from the lead(brown wire) to the positive side of the battery.
I assumed when I read this, that the brown wire was still connected when you measured this, and the key switch was in position #1; I also assumed the tail light was on, indicating the brown wire is at a ground. I still haven't figured out how the headlamp wires, white or green, are involved, as the white and blue wires should not be connected to anything when the switch is in the off position, and the green wire is the common ground. It's as though the green wire goes directly to the tail lamp, but nowhere else. There is a ring terminal from the harness to the negative terminal of the battery, connected with the large cable that goes to the back of the transmission and frame - is it there, and can you measure it to the green connection in the headlamp?
 

·
Registered
Joined
·
7 Posts
Discussion Starter · #12 ·
I assumed when I read this, that the brown wire was still connected when you measured this, and the key switch was in position #1; I also assumed the tail light was on, indicating the brown wire is at a ground. I still haven't figured out how the headlamp wires, white or green, are involved, as the white and blue wires should not be connected to anything when the switch is in the off position, and the green wire is the common ground. It's as though the green wire goes directly to the tail lamp, but nowhere else. There is a ring terminal from the harness to the negative terminal of the battery, connected with the large cable that goes to the back of the transmission and frame - is it there, and can you measure it to the green connection in the headlamp?
I will check it out when I get a moment, thanks again. I just think it is strange that the headlight switch is off and the white wire affects the tail light in any way. The light goes off if you unplug the white or green wire from the headlight.
 

·
Premium Member
Joined
·
5,765 Posts
That's what has me concerned about the wiring; the only connection between the white wire and the tail lamp is the common green ground wire. The blue wire doesn't make a difference?
 
1 - 13 of 13 Posts
Top