Author Topic: Tail light won't illuminate (Read 1696 times)

JBend · « **on:** November 23, 2019, 09:54:51 am »

Two weeks ago I bought a new wiring harness off 4-1, all my lights work except my tach and speedo gauge and my tail light won't stay lit. Brake light, turn signals, HB and LB work. It seems as if I get no juice from the brown wire dealing with the tail light harness. Is this a fuse? Thanks, bit of a rookie here.

1977 CB750f super sport

HondaMan · « **Reply #1 on:** November 23, 2019, 06:07:09 pm »

Quote from: JBend on November 23, 2019, 09:54:51 am

Two weeks ago I bought a new wiring harness off 4-1, all my lights work except my tach and speedo gauge and my tail light won't stay lit. Brake light, turn signals, HB and LB work. It seems as if I get no juice from the brown wire dealing with the tail light harness. Is this a fuse? Thanks, bit of a rookie here.

1977 CB750f super sport

Yes, there is a fuse for the taillight. It will be the top one in the F2 fuseholder. If your fuse clips are corroded, they will either not pass much current, or may melt the fuse, making it look like it 'blew' when carrying normal current.

Did you get a new fuseholder?

JBend · « **Reply #2 on:** November 24, 2019, 07:44:56 am »

I did not. I'll order one and new fuses just to be safe.

Thank you sir.

JBend · « **Reply #3 on:** November 24, 2019, 10:29:37 am »

I put a new fuse in and still nothing, everything else still works though.

JBend · « **Reply #4 on:** November 24, 2019, 01:26:32 pm »

So I now tried to change the fuse and now my bike won't start...the headlight lights up and brake light, now I have no turn signals and the bike won't fire. WHAT HAVE I DONE

minimo · « **Reply #5 on:** November 24, 2019, 01:45:16 pm »

Check your fuses. Did they blow?

Simplify the wiring connections.
You said you replaced the entire harness with a new so chances are there’s some crossing of wires somewhere?

I would disconnect all gauge and turn signal lights and troubleshoot these connections one by one after you focus on getting the bike to start again. Once you get your bike started again, then reintroduce the gauge and signal and brake lights one component at a time. This is also where a multimeter would come in handy to check continuity. Harbor Freight sells one for like $5.

Also, per Hondaman’s suggestion, did you clean the contacts on your fuse holder? Dremel with a brass wire wheel will buff it up real nice. Take time to clean up all of the contacts/connectors receiving the plugs from your fresh wire loom.

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JBend · « **Reply #6 on:** November 24, 2019, 02:03:25 pm »

The top fuse holder is good where the tail light fuse is located, the bottom two aren't getting continuity. Can cleaning them solve the problem or do I need a new fuse box? I'm just confused as to how I did this. I took it to a dealer to get some work done and it ran fine Friday evening. Sat yesterday and now this today. So lost.

minimo · « **Reply #7 on:** November 24, 2019, 02:21:03 pm »

Yes. Clean the contacts where the glass fuse ends clip in. Meanwhile, verify continuity across fuse ends and also make sure you have correct amperage of fuses: Taillight 5A, Main 15A, Headlight 7A

While you’re at it, make sure the solder/connections across the wires on the flip side to the fuse holder are all intact.

Pictures here to show us might help.

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minimo · « **Reply #8 on:** November 24, 2019, 02:25:55 pm »

But again, after giving a thorough clean and polish of the fuse holder, I would simplify the set up and focus on getting the bike to start so keep the Main 15A fuse in there (as long as it’s still good), pull out the others. Chances are you have a ground fault shorting out your system via the wiring for lights

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minimo · « **Reply #9 on:** November 24, 2019, 02:28:58 pm »

While you’re at it too, meter your battery. Make sure you have at least 12.4V

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JBend · « **Reply #10 on:** November 24, 2019, 02:42:43 pm »

Just did a test on all fuses and fuse holders and they're fine. Both the starter and regulator are fine as well as the two 6 prong and 5 prong clips below the fuse holder and the turn signal male and female ends. Nothing seems to be bad. Also bought a brand new battery and spark plugs last Monday.

JBend · « **Reply #11 on:** November 24, 2019, 02:46:27 pm »

Assuming this is why it won't start now. That's my battery voltage

minimo · « **Reply #12 on:** November 24, 2019, 02:46:39 pm »

So you did update the fuse holder - good thing too and that they’re the blade-type and not the bulbs.

Your fuse sequence though doesn’t follow the OEM; I see that your 15A Main is at the bottom. Verify that you have that all correct and corresponding with the mating harness...

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minimo · « **Reply #13 on:** November 24, 2019, 02:50:46 pm »

Hopefully you’re not running a LiFePo battery. That reading would make it a brick.

Charge it up to the max.

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JBend · « **Reply #14 on:** November 24, 2019, 02:52:21 pm »

Going to be honest, not sure what a lifepo battery is.

minimo · « **Reply #15 on:** November 24, 2019, 03:01:18 pm »

Lithium Iron Phosphate.

Hopefully your battery is not that.

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JBend · « **Reply #16 on:** November 24, 2019, 03:06:09 pm »

It's an AGM?

minimo · « **Reply #17 on:** November 24, 2019, 03:06:42 pm »

Charge ‘er up.

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JBend · « **Reply #18 on:** November 25, 2019, 12:43:45 pm »

Ended up getting full charge and that was the problem. Started to ride it down to get it registered and she just died on me. Come to find out it was a faulty, brand new battery which caused it to blow a fuse. New battery, new fuse, one cheeseburger later she's moving fine and registered. Thank you both for all the help.

minimo · « **Reply #19 on:** November 25, 2019, 01:15:22 pm »

As is often the case with electrical issues, start simple. We often jump to conclusions for the issues we can’t readily see.

Glad you were able to sort this out.

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minimo · « **Reply #20 on:** November 25, 2019, 01:23:58 pm »

And hopefully it was just a faulty battery; strange that after a full charge that it would die out on you again after a ride.

If this replacement battery exhibit the drain again, inspect your regulator.

Meanwhile, I hope you’ll be cleaning up all of your contacts anyway because that can also be a source some draw of power...

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JBend · « **Reply #21 on:** November 25, 2019, 02:04:38 pm »

😂😂😂 happened again with the new battery after I rode it for a few hours, so here we go. It's an AutoZone duralast gold, so idk. Just more worried about someone snagging it while it's sitting out.

minimo · « **Reply #22 on:** November 25, 2019, 02:23:01 pm »

Those batteries should be pretty fault-proof, especially purchased new and starting from a full charge (about 14.4V).

There’s a drain somewhere in your system. Again , simplify. Remove the idiot lights and signals before troubleshooting from a full charge; you want to rule out the obvious, though you could have some regulator issue - I’d check to make sure corresponding colors between mated harness match.

Get home safe, spiff up ALL of your connections, invest in some Electrical Contact Cleaner, make sure you have a good charge on battery, inspect your reg...

JBend · « **Reply #23 on:** November 25, 2019, 03:22:38 pm »

Just got home and tested the battery and it's at 10.5, is that low for a couple of hours riding maybe? With multiple stops and starts? I didn't check the volts on the regulator but it was good last night when I checked

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Author Topic: Tail light won't illuminate (Read 1696 times)