Triumph Rat Motorcycle Forums banner
  • Hey everyone! Enter your ride HERE to be a part of this month's Bike of the Month Challenge!
1 - 20 of 24 Posts

·
Registered
f'd up 2009 Thruxton. It will kill me one day.
Joined
·
17 Posts
Discussion Starter · #1 ·
Hi chaps.

I have an interesting electrical conundrum that I would like a little more insight into. I don't know much about electrons, so hopefully someone who knows knows.

I recently took the wiring harness out of my 2009 Thruxton, and replaced it with a new one. The new one had been spliced to add running lights, brake lights, and turn signals for a sidecar.
Shortly after testing that everything went well, I unplugged the sidecar and went off for a ride. When I got back, the turn signals, brake light, and horn were not working.
Obviously, the fuse was blown. On the air-cooled twins the turn signal, brake light and horn are on the same fuse, I would not be surprised if that was normal for most bikes but have never looked.
So, about a year ago I took the rusted old Triumph horn out and put in a Fiamm Freeway Blaster. I live in a trafficy area and am not afraid to use the horn to let folks know I'm there, not rude, just gentle little toots to alert other road users. The Fiamm has been GREAT for most of the last year.

Anyway, a session with the multimeter showed that the Fiamm was drawing about 9 Amps, and when combined with turn signals or brakes, the fuse was blowing.

Here is the question: I've had the Fiamm horn for about a year, used it a lot, and it never blew the fuse. Obviously, I never checked the current on it either. Is it possible that changing the harness caused the current to change in the wiring in general? I've looked for shorts but haven't seen any yet, and the splicing is not complex wiring. Is it possible that the different wires could cause higher current, or is that just utter nonsense?

Follow up: I fitted a 1.5A rated horn from Amazon and it is working fine. It sounds comedically shrill, but it did just alert a Honda to my presence and stopped someone from pulling out in front of me, which is nice. It seems to have stopped the fuse blowing, which is also a bonus. I'm kind of tempted to put a relay on and put the Fiamm back, but if there is an actual real issue in the wiring that I need to take care of, I would rather get that fixed first :D


Yours,


MUPPET


The connection work is not finished yet, but here is a gratuitous picture of the bike and the sidecar. See those sidecar lights? Nice. The bimmer you see parked behind it also has a Fiamm horn, but no sidecar.
757292
 

·
Registered
2017 Bonneville T100
Joined
·
452 Posts
Is it possible that the different wires could cause higher current, or is that just utter nonsense?
If the new wire is heavier gauge than the old, then it will have less resistance and would increase current. There probably wouldn't be much difference. But, perhaps it was right on the edge before the new wiring, and the new wiring allowed just enough additional current to be a problem. It's also possible that in there were some marginal connections with the old harness that were reducing current consumption by the horn.
 

·
Registered
Joined
·
1,705 Posts
Nine amps seems a bit high for a horn.... If the new wire has less resistance than the old wire, whether from being newer or bigger it will lessen the load on the fuse and make it less likely to blow. More resistance from old or smaller wire would make the fuse more likely to fail.
The OE wiring for the horn and headlight on these bikes is the bare minim. Any horn you use will be better, louder with battery voltage supplied through a bigger wire and a relay. Headlight can also be improved with relays.
 

·
Registered
f'd up 2009 Thruxton. It will kill me one day.
Joined
·
17 Posts
Discussion Starter · #5 ·
The answers thus far give me much relief. I suspect it was right on the edge, and the new wire tipped it. Or even the newer pins in the taillight assembly connector, more than likely, as they are also slightly thicker. The new harness is a Motone harness. Next steps are to change the brake lights to LEDs, add a relay and put the big-ass horn back, and keep on testing testing testing.

Much obliged, gentlemen.
 

·
Registered
2022 Triumph Bonneville Street Twin
Joined
·
383 Posts
a 20 gauge wire has 10.15 ohms resistance per 1,000 feet
1 foot= 0.01015 ohm

a 14 gauge wire has 2.525 ohms resistance per 1,000 feet
1 foot=0.002525 ohm

Compared to the resistance of the horn, the difference is negligible.

A "good" connection from battery negative to motor/frame is about 0.1 ohm

Is the horn resistance about 1.33 ohms?

Are the horn connections good?
 

·
Registered
2022 Triumph Bonneville Street Twin
Joined
·
383 Posts

·
Premium Member
Joined
·
1,521 Posts
Max current draw on those horns is officially 6A. The gauge of wire won't affect things unless it's particularly flimsy, but most bike horn switches and circuits are only designed for the stock horn. Your horn uses 72W, which is more than a headlamp, so you may need at least a 10A fuse. If it keeps happening then fit a relay and run it from a dedicated fuse.
If it didn't used to have an issue then you may have had higher resistance wire, but it's more likely that your fuse was close to blowing each time you used the horn, and the replacement may just be quicker blowing.
9A is very high though, as that's 108W, so you may also have an issue with the horn itself.

Sent from my SM-G998B using Tapatalk
 
  • Like
Reactions: SportsterDoc

·
Registered
2017 Bonneville T100
Joined
·
452 Posts
Nine amps seems a bit high for a horn.... If the new wire has less resistance than the old wire, whether from being newer or bigger it will lessen the load on the fuse and make it less likely to blow.
That's backwards. Lower resistance means higher current means fuse more likely to blow.

That said, the resistance difference between 14g and 16g wire is pretty small, and unlikely to be the issue.
 

·
Registered
Joined
·
610 Posts
Well, if changing the wiring harness affected current draw, then you were lucky you had a fuse because your wiring must have been adding non-trivial resistance, which is a big fire risk.

The correct answer is: run that horn on a relay. With big wire. I'd run 14ga.
 

·
Registered
Joined
·
42 Posts
Nine amps seems a bit high for a horn.... If the new wire has less resistance than the old wire, whether from being newer or bigger it will lessen the load on the fuse and make it less likely to blow. More resistance from old or smaller wire would make the fuse more likely to fail.
The OE wiring for the horn and headlight on these bikes is the bare minim. Any horn you use will be better, louder with battery voltage supplied through a bigger wire and a relay. Headlight can also be improved with relays.
Sorry, but exactly the opposite is true.
 

·
Registered
Joined
·
7 Posts
jsobell has it right but nobody noticed. The horn is going bad as it draws 9 amps instead of 6. The fuse did it’s job by blowing when the total current exceeded it’s limit.It was just a coincidence that the current draw of the horn went up when the harness was changed. If you liked that horn get another and measure the current draw right away to make sure it meets spec. Maybe the old horn is under warranty?
 

·
Premium Member
Joined
·
482 Posts
...........If the new wire has less resistance than the old wire, whether from being newer or bigger it will lessen the load on the fuse and make it less likely to blow. More resistance from old or smaller wire would make the fuse more likely to fail.
Umm, I don't think this is correct. "Resistance" is resistance to current flow. Less resistance allows more current, fuses are rated to limit whatever current (amperage or amps) they are rated for. So a better connection (larger wire) will allow more current to flow in the circuit. Think of it this way: A direct short is the least amount of resistance you can get in a given circuit. That is what fuses are there to protect against.
 

·
Registered
Joined
·
1,705 Posts
Umm, I don't think this is correct. "Resistance" is resistance to current flow. Less resistance allows more current, fuses are rated to limit whatever current (amperage or amps) they are rated for. So a better connection (larger wire) will allow more current to flow in the circuit. Think of it this way: A direct short is the least amount of resistance you can get in a given circuit. That is what fuses are there to protect against.
My bad... I may have been mistaken about resistance blowing fuses but stand by the fact that by-passing small, long wires with a relay to the horn and headlight will improve them. Also small, dirty or loose connections cause resistance and heat, sometimes so much so that the plastic around the connection is destroyed or the wire is burned in two.
 

·
Premium Member
Joined
·
482 Posts
My bad... I may have been mistaken about resistance blowing fuses but stand by the fact that by-passing small, long wires with a relay to the horn and headlight will improve them. Also small, dirty or loose connections cause resistance and heat, sometimes so much so that the plastic around the connection is destroyed or the wire is burned in two.
Absolutely. Resistance in a connection is never desired. Proper crimps are especially important, or I'll solder whenever I can. I don't know how many times I've had to replace wire terminals that had been crimped with cheap auto store wire crimpers, or worse yet, pliers or visegrips. It'll work, for awhile, but never a long term solution.

Any time you add an aftermarket item, such as a horn, that draws more current than the original circuit was designed to handle, it is best to run a dedicated circuit for it with it's own properly rated fuse and appropriately gauged wire. In the case of the horn, you can
use the original circuit for the control side of the relay, and a dedicated circuit with it's own fuse for the load side of the circuit. I did just that when I installed an air horn.
 

·
Registered
2022 Triumph Bonneville Street Twin
Joined
·
383 Posts
jsobell has it right but nobody noticed. The horn is going bad as it draws 9 amps instead of 6. The fuse did it’s job by blowing when the total current exceeded it’s limit.It was just a coincidence that the current draw of the horn went up when the harness was changed...
The rated current draw was not known when the model # was asked in post 8.
Most likely the horn coil was partially shorted, so that only part of the windings were in the circuit.
 

·
Registered
2018 T120 & 2000 Ducati Monster 900
Joined
·
248 Posts
You added a side car, with additional lighting for brakes running and turn signals.
This added additional load on that circuit which the fuse controlled. It could exceed the fuse rating.
The horn drawing the 9 amps as stated is probably going bad.
I would use a relay to activate an aftermarket horn, horn power fused from battery through relay contacts, relay activated from horn switch.
it's a math problem to add up all the light wattage then divide that number by 12 gives the amperage (current) steady state. with flashing lights (turn signals add 33% to the wattage for the surge of current draw).
This would give nominal fuse size which is then increased by 10% to the next closes size.
 

·
Premium Member
Joined
·
1,521 Posts
The rated current draw was not known when the model # was asked in post 8.
Most likely the horn coil was partially shorted, so that only part of the windings were in the circuit.
I just looked up the rated current for the horn stated in the original post on the manufacturer's website.
Always best to use facts, not guess

Sent from my SM-G998B using Tapatalk
 

·
Registered
2022 Triumph Bonneville Street Twin
Joined
·
383 Posts
Always best to use facts, not guess
Yes and why I asked Muppet the model number (AM-80S high or low) and provided a link to the catalog so that he could see normal current draw, since he was tempted to continue to use the Fiamm, but with a relay.
 
  • Like
Reactions: jsobell
1 - 20 of 24 Posts
Top