fitted LED head light now gas guage always reading full - Triumph Bobber Forum
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  • 4 Post By Mar-Vel
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post #1 of 7 (permalink) Old 04-30-2019, 11:09 AM Thread Starter
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fitted LED head light now gas guage always reading full

Hey guys...Has anybody else switched out their stock head light for an aftermarket LED . Now I cant for the life of me think why this Is related but ever since doing this my gas gauge Is reading full all the time . The stock head light has five wires going into It , the after market has just the regular three wires , running light head light main beam which all work well , so I had two wires left over have no clue what they do I think they were blue and yellow so I just taped them up and went on my merry way . I know the sensible thing to do Is re attach the stock light and see If that cures the problem , but the light was not plug and play I had to splice the wires so not a five minuet job .

Any thoughts/ideas ?......Thanks .

Last edited by Mar-Vel; 04-30-2019 at 11:13 AM.
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post #2 of 7 (permalink) Old 04-30-2019, 11:18 AM
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Hi Mar-vel,

No idea mate.

The whole modern electric thingy on these bikes has me totally lost. I did have my headlight switched out for a Speedmaster one (not the same I know) with no issues.

Good luck and hope someone can help.


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post #3 of 7 (permalink) Old 04-30-2019, 12:46 PM
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My guess is that when you spliced the wires something either got shorted to ground or set at +12V continuously.
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post #4 of 7 (permalink) Old 04-30-2019, 01:12 PM
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Well, based on the gauge reading at least, no doubt you’re now getting better mileage than all of us...put together. 🤔. Not that I ever go by the gas gauge anyway, (just the trip mileage) but, I suppose it would be nice if it read even close to correct. Hope U find a solution shortly.
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post #5 of 7 (permalink) Old 04-30-2019, 04:16 PM
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Is the replacement light designed specifically for the Bobber Like the ones A&JCycles sell

Next, and Please don't take this the wrong way, but are you sure you hooked up the right wires to the new headlight? I included a pic of the original setup (from the Haynes Manual).

If everything is hooked up right, My first thought is a change in the circuit resistance is the issue. Your fuel gauge is basically a linear variable resistor, so a change in resistance in the circuit could make it do funky stuff

It maybe as Psychopasta said,, something is bad touching something it shouldn't be.. Are you getting any DTC codes? specifically P1619 or P1620? Either of those would indicate a short in the headlight circuit, Or, have you noticed anything else not doing what its suppose to?

If Not:

Did you leave the plug for the side light intact? Try plugging the side light bulb back in first. If that doesn't fix it, try a quick wire tie together with the original light. If reconnecting either or both light(s) "fixes" it, and I'm making something of a leap here, Having that bulb out/disconnected is causing some sort of power deviation that is messing with the computer, and the result is the fuel gauge. It maybe that you need to "add" that resistance back into the circuit..

So if either of those fixes it. You need to determine the resistance of the bulb, (ie use an ohm meter between the bulb contacts) and try putting a resistor or two in place of the bulb, which fools the computer into thinking the bulb is functioning right. An example I know of is, if you replace a normal incandescent 194 bulb with a non resistance matched LED bulb, you need to add a 1/8th watt 1k ohm resistor to it to make things work right.

Alternatively, if it's the side light, you could add a halo ring (somebody had a thread about that recently) using those wires as the power, so the computer thinks everything is ducky and not do weird stuff....I had a quick look at the wiring diagram (also attached in PDF form: Part 1,Part 2) and don't see any physical connection between those circuit's, but that does not mean much once it hits the computer.

If none of this long winded diagnostic works, could be the sender itself took a spike of some sort which seems unlikely but you never know, in which case, sender time.

Or worst case (least likely) scenario, the computer took a hit

Hope something here helps, Good Luck!
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Last edited by Great Black North; 04-30-2019 at 04:25 PM.
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post #6 of 7 (permalink) Old 04-30-2019, 10:02 PM Thread Starter
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Hey GBN thanks for the input....although Its an LED light Its not specific for the BB , everything on the light works fine , The light in your picture Is different to the BB see pic below , the only connection to the stock light Is under the tank , the aftermarket light harness Isn't long enough to reach under the tank , one reason I had to splice It . No codes on the dash everything Is fine except for the gas gauge .

So I reconnected the stock light , gauge was still reading full there are a couple of things Im going to try tomorrow so fingers crossed . one other thing came to mind , after I fitted the light I knew I needed gas and the gauge was reading almost empty filled the tank up and the gauge read full , trouble Is Its stayed there .
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post #7 of 7 (permalink) Old 05-01-2019, 11:49 AM Thread Starter
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Ok I got It sorted....Gauge Is now working . I rewired the halo to the factory harness which It wasn't before , I thought It wouldn't hurt to disconnect the battery for five minuets maybe It might reset something ....Anyway took It for a long ride and bingo Its reading 1/4 full .
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