Tailight Issue

[cyclespun]

I know its been covered before but after following all the troubleshooting posts I am at a loss.

I have a 77 shovel, Tombstone tailight 3 wire. Worked before and now it doesn't. Checked all the wiring, its good. Routing is good. Reworked the ground to ensure it has a good ground. Checked all the connection points and they are good. Checked bulb, both hi and low work on the bulb itself. Both bulb nodules inside the socket are working and reading around 11 or higher for running and brake light. Battery is fully charged. I am not sure where the issue is since the nodules are reading correctly and routing is correct. and ground is good. That usually solves my issues I have had in the past. Turn the key, headlight and everything works. Tailight will just not light up.

Any help is appreciated...

[armand]

It would seem that you should be getting 12 volts at the light vs 11 v. But I’m guessing that your bulb is not touching the bumps in the base of the socket.

[TriNortchopz]

What is the ground wire grounded to? fender? frame? engine?
What is voltage reading at battery? should be EDIT; close to the same at bulb socket 'nodules', varying due to resistance across switches and connections.

[10scDust]

Beating myself up over similar issues, I now run a dedicated ground wire to all my lighting when building, or reworking one of my rides.
I run it to the lights mount bolt and back to the frame ground location, wherever its located, except the front forks, there I run a braided copper ground wire from lower triple tree back to the frame, or engine tucked neatly away (I have amassed a few from my old demolition derby days where they used them from firewall to engine, trunk lid to body, firewall to hood, etc).

I also use electrical de-oxidizer grease (di-electric) at all my connections.

I've dealt with plenty of corrosion issues from rain water, or weather conditions (read humidity) getting to connections and such under side covers, sometimes under light lens from a faulty gasket & the bulb socket suffered.
My 1991 Ultra was always doing bad like that where the CB connections were under that side cover, I was young, live and learn.

[cyclespun]

It would seem that you should be getting 12 volts at the light vs 11 v. But I’m guessing that your bulb is not touching the bumps in the base of the socket.

I’m getting 12 volts after charging the battery at the lights. And the bulb is touching in the base of the socket on the nodules. Still nothing

[cyclespun]

What is the ground wire grounded to? fender? frame? engine?
What is voltage reading at battery? should be same at bulb socket 'nodules'.

Ground is wired to the underside of the fender. I grinded down all the paint and it is bolted straight to the steel. So ground is solid. Still no light

[JBinNC]

Ground is wired to the underside of the fender. I grinded down all the paint and it is bolted straight to the steel. So ground is solid. Still no light

Best to run the ground back to the frame, on an H-D, the lug for the battery ground cable is a natural place. The reason to run a ground wire to start with is that any of the components, like the fender, may not be fully grounded due to paint, powder coat, corrosion, etc.
And I will differ from T's post, above, in that you will usually NOT see exact battery voltage at any accessory due to voltage drops across switches and wiring. But the aggregate drop should be below 5%, or roughly .6V in a 12V system. With the motor running and the voltage elevated to alternator or generator output voltage, the reading at any accessory should be well above the rated 12V.

Jim

[cyclespun]

Okay so what I have done now is unplugged the two wires from the brake switch. Both are reading 12v and when I put a paper clip in them nothing happens. But when I touch the paper clip to the exhaust it sparks the wire and the tailight comes on ... What could this indicate?

[cyclespun]

And what I mean is I put a paper clip to connect the two wires to jump them together

[cyclespun]

Both of the wires that go to the brake switch have are hot. From what I understand only one should be hot

[JBinNC]

Both of the wires that go to the brake switch have are hot. From what I understand only one should be hot

That is a classic indication of a BAD GROUND on a two filament taillamp or turn lamp fixture.

There is another possibility that one of the filaments in the bulb has broken and then welded itself to the other filament. Replace the bulb to diagnose.

Jim

[TriNortchopz]

You got a front brake connected to brake light switch...is that what you mean, "two wires"

[cyclespun]

That is a classic indication of a BAD GROUND on a two filament taillamp or turn lamp fixture.

There is another possibility that one of the filaments in the bulb has broken and then welded itself to the other filament. Replace the bulb to diagnose.

Jim

Hey Jim, so I tested the light itself and the bulb is working. Looks fine inside and out too

[cyclespun]

You got a front brake connected to brake light switch...is that what you mean, "two wires"

No front brake. Kick only bike. I’ve tried grounding the rear tailight wire onto the battery itself instead of the bottom of the fender which is raw steel as well. I tried grounding the wire to a few different spots and still nothing. Which makes me believe my ground is fine...

[TriNortchopz]

wire to taillight pinched?

[cyclespun]

wire to taillight pinched?

No pinched wires anywhere. But that that was one of my assumptions too.

[cyclespun]

I put a new bulb in. Lit up then turn it off, put it back together with light case and all that. Then went to switch it on again and nothing. Then it would come on sometimes when I flipped the switch then other times it wouldn’t. Now it won’t at all again...

[TriNortchopz]

That sounds like poor connections in the switch; what kind of switch is it?
got a test light or a volt/ohmmeter to check for poor connection through the switch?

[cyclespun]

I’ll send a photo of the switch. It’s a thread in style with the two prongs like an outlet plug. I’ll check the switch. But what really has me is the two female plugs that plug onto the switch are both hot and reading the same as my battery. I thought one is suppose to be hot and one is suppose to be not

[cyclespun]

That sounds like poor connections in the switch; what kind of switch is it?
got a test light or a volt/ohmmeter to check for poor connection through the switch?

Reply to yours above^