Lack of fusing

[Kiwi_Roy]

While I was looking at a problem with a LeMans II on the forum I noticed that Luigi in his wisdom had neglected to put a Fuse in the ignition circuit, No fuse between battery and ignition switch or anywhere in the coil circuit, I wonder how many older Guzzi's have gone up in smoke over the years because of this oversight?

If you have an older Guzzi might I suggest you fix this problem,
Cut the main red wire at the battery and add a separate 40 Amp in-line fuse. This fuse will be more than enough to supply any normal load.
If you get a short at the ignition switch or in the fat Brown wire between the switch and the fuse panel this fuse will blow and save the bike.
What made Luigi do this, I don't know but haven't we been plagued by Startus Interuptus for many years, proving that the factory have no clue as to how wiring needs to be done,
Rant over
http://www.thisoldtractor.com/guzzi007/schematics/1978_LeMans_II.gif
The Red wire to the ignition switch is Unfused so when the switch is On the white wire to Kill Switch and ignition coils is also unprotected.

Cheers
Roy
Update:
           I couldn't find a 40 Amp blade fuse therefore I will revise rating to 30 Amps

[bigbikerrick]

Good advice, Roy. I imagine my 76 convert is wired up the same way. Its definitely something to check out.
Rick

[nc43bsa]

I've never understood this level of penny-pinching. 

Ford did the same thing, with their unswitched, unfused hydraulic brakelight switch that was prone to leaking, causing 1000s of fires which, in turn, burned down 100s of homes.

Ford's solution was to recall those vehicles and install a fuse on that circuit.

[Kiwi_Roy]

Good advice, Roy. I imagine my 76 convert is wired up the same way. Its definitely something to check out.
Rick

Now you mention it I also have a 76 Convert, I need to add a fuse to it also.
As I mentioned in my original post the easiest thing to do is add a main fuse in the red wire from battery to ignition switch.
I figure a 40 Amp 30 Amp blade fuse is probably appropriate, it will melt well before the wires in the loom. It also provides a handy point for isolating the wiring, pull the fuse to work on anything rather than having to disconnect the battery.
Note: Some Guzzi's don't run the switch feed from the battery post but tap onto the large starter cable at the starter solenoid so add a fuse there.
It's not practical to fuse the starter solenoid feed, that would likely require <150 Amp fuse.
I wouldn't trust Luigi as far as I could throw him when it comes to wiring.

[Antietam Classic Cycle]

I've never heard of any old Guzzi "going up in smoke" due to there not being a fuse there. <shrug>

[moto]

... As I mentioned in my original post the easiest thing to do is add a main fuse in the red wire from battery to ignition switch.
I figure a 40 Amp blade fuse is probably appropriate, it will melt well before the wires in the loom.
...

This suggestion seems inadequate.

A 40 Amp fuse will pass 40 Amps of current to the rest of the circuit before blowing. But the ignition circuit wiring won't handle that current.

The smaller gauge wires in Guzzi looms are 1 square millimeter in section. This places them between 16 and 18 AWG, as seen in this table:





Letting the larger cross-section 16 AWG wires stand in for the smaller Guzzi wires, the next table shows how much amperage a 16 gauge wire can safely carry. In the table, the safe amperage depends on whether the wire will heat itself above the melting point of each of three different types of insulation.





The table indicates 16 AWG wire can safely carry around 17 Amps before insulation melts. This means the 40 Amps passed by the suggested fuse will cause both 16 AWG, and the smaller 1 square millimeter Guzzi wire, to fail. (Assuming the old Guzzi wire has insulation that is no better than any of listed modern types.)

There are complexities in calculating ampacities of wire in different applications but this table from Home Depot suffices as a rough guide for this problem.

All this aside, I agree with Charlie's observation that old Guzzis don't burst into flames because of the lack of fusing. Though I worried about this in the past I have lately adopted his attitude. If I were worried I might put a 15 Amp fuse in the ignition circuit.

[Kiwi_Roy]

This suggestion seems inadequate.

A 40 Amp fuse will pass 40 Amps of current to the rest of the circuit before blowing. But the ignition circuit wiring won't handle that current.

The smaller gauge wires in Guzzi looms are 1 square millimeter in section. This places them between 16 and 18 AWG, as seen in this table:





Letting the larger cross-section 16 AWG wires stand in for the smaller Guzzi wires, the next table shows how much amperage a 16 gauge wire can safely carry. In the table, the safe amperage depends on whether the wire will heat itself above the melting point of each of three different types of insulation.





The table indicates 16 AWG wire can safely carry around 17 Amps before insulation melts. This means the 40 Amps passed by the suggested fuse will cause both 16 AWG, and the smaller 1 square millimeter Guzzi wire, to fail. (Assuming the old Guzzi wire has insulation that is no better than any of listed modern types.)

There are complexities in calculating ampacities of wire in different applications but this table from Home Depot suffices as a rough guide for this problem.

All this aside, I agree with Charlie's observation that old Guzzis don't burst into flames because of the lack of fusing. Though I worried about this in the past I have lately adopted his attitude. If I were worried I might put a 15 Amp fuse in the ignition circuit.

Sure you can wire the whole bike without any fuses if that's what you want to do.
Having worked in electricity related for the past 60 years it goes against the grain to have unprotected wiring, put a 15 Amp fuse in your ignition.

[Antietam Classic Cycle]

"A solution in search of a problem." 

[FarmallA]

The wire will blow to protect the fuse.

FarmallA
Steve

[moto]

Sure you can wire the whole bike without any fuses if that's what you want to do.
Having worked in electricity related for the past 60 years it goes against the grain to have unprotected wiring, put a 15 Amp fuse in your ignition.

My post was to demonstrate the error of your suggestion that a 40 amp fuse would protect things.
I finished up suggesting a 15 amp fuse in the circuit.

The long circuit from the ignition switch to the handlebar end and then to the coils deserves a fuse. In particular it deserves its own fuse, since the failure of some unrelated component should not shut down the ignition! The T3's were delivered with two empty fuse positions in the fuse box (F5 and F6) that are available for a dedicated fuse.

I'm with Roy in my surprise that fusing was omitted, but like Charlie I take comfort in the apparent lack of resulting real problems. Even though indifference seems to be working, Roy's concern is appropriate.

[Kiwi_Roy]

The wire will blow to protect the fuse.

FarmallA
Steve

Do you know that for sure, have you tried it?

[Moparnut72]

I worked in a motorcycle rental shop in the late 60's. We had a fleet of Hondas, the 175's were prone to the rectifier shorting out unexpectedly. There were no fuses so the smoke would be released from the wiring going to the headlight nacelle. When the wiring burnt through the next path was through the speedometer cable destroying it. It happened three or four times. We should have fused the harnesses. I was in the Army and worked after hours and weekends so I didn't have a lot of say.
kk

[FarmallA]

Do you know that for sure, have you tried it?

If you mean have I intentionally shorted a 14 or 16 ga wire to see if a 40 amp fuse will keep my bike from burning down, then no, I haven’t. But there is no wire anywhere on any of my bikes that will be protected with a 40 amp fuse.  Except for the big 6 ga wire from the battery to the starter solenoid.

I have several outboard motorboats. The main bus from the batteries to the starter solenoid is protected (perhaps) with a 150 amp fuse; the starter motor on a 1964 28hp 2 stroke Johnson will blow a 40 amp.  (I have tried that). Everything else is (hopefully) protected with 15 amp fuses.

“The circuit will blow to protect the fuse” is an old, well known adage. I didn’t make it up.

FarmallA
Steve

[Kiwi_Roy]

If you mean have I intentionally shorted a 14 or 16 ga wire to see if a 40 amp fuse will keep my bike from burning down, then no, I haven’t. But there is no wire anywhere on any of my bikes that will be protected with a 40 amp fuse.  Except for the big 6 ga wire from the battery to the starter solenoid.

I have several outboard motorboats. The main bus from the batteries to the starter solenoid is protected (perhaps) with a 150 amp fuse; the starter motor on a 1964 28hp 2 stroke Johnson will blow a 40 amp.  (I have tried that). Everything else is (hopefully) protected with 15 amp fuses.

“The circuit will blow to protect the fuse” is an old, well known adage. I didn’t make it up.

FarmallA
Steve

I thought today I should try it, I took about 6 feet of 16 gauge and connected in series with a blade fuse holder.
I couldn't find a 40 Amp blade fuse, I don't think they make anything over 30.
I connected the fuse and wire to a set of jumper cables and the other end to my car battery, the fuse blew instantly with no heating of the 16 gauge copper wire.
While trying to find a 40 amp fuse at my local dealers I did find out that the element in blade fuses is Zinc, this metal has a higher specific resistance than copper hence for the same CSA it will heat up much quicker.
I still maintain there should be a fuse to protect the ignition switch.

Rant over
Roy

[moto]

I thought today I should try it, I took about 6 feet of 16 gauge and connected in series with a blade fuse holder.
I couldn't find a 40 Amp blade fuse, I don't think they make anything over 30.
I connected the fuse and wire to a set of jumper cables and the other end to my car battery, the fuse blew instantly with no heating of the 16 gauge copper wire.
While trying to find a 40 amp fuse at my local dealers I did find out that the element in blade fuses is Zinc, this metal has a higher specific resistance than copper hence for the same CSA it will heat up much quicker.
I still maintain there should be a fuse to protect the ignition switch.

Rant over
Roy

Excellent. I have been rummaging around. I do have 1-square mm wire (thinner than 16AWG), and I did find 40A blade fuses for sale on Amazon. Doing the test would require money for a good quality fuse (LittelFuse, at $7.50. Search for Littelfuse Maxi Blade Fuse, Orange 40 amp on Amazon.) But just how obsessive am I?

The point about zinc is a good one.

6 feet is about the right length. The longer the wire the greater the total resistance, but I don't think that will matter much here.

It is still true that we should be using about a 15A fuse for the ignition circuit. Whether I will add one to my own bike, I don't know.

Moto

[John A]

 , I use small automatic reset circuit breakers mostly unless a fuse is more appropriate.