Mine was documented, as KG 5. The Brough on display in the Imperial War Museum, was the last Brough purchased by Lawrence, but he died before taking delivery. I've even heard that he owned 11 Brough Superior SS 100's plus a Grand Alpine Touring Model, that could change final drive sprockets, on the run, like a derailleur on a bicycle. I've never see one though. They were rare to begin with, I think all told less than 2000, total production for all models from 1921 to 1939. Brough switched over to ball bearing production, and never manufactured motorcycles again. I've heard that most were melted down at the start of WWII, but I don't know if that's an urban legend.
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Here's a tidbit that I read in the History of Motorcycles. In 1936 the world record runs were held on Daytona Beach, in Florida. A Brough Superior SS 100, made a one way run at 186 MPH, on the return run, the motorcycle went airborne, killing the rider. Harley Davidson ran both ways setting the world record at 136MPH on the Knucklehead EL. 50 MPH slower.

When they do come up for sale they fetch 6 figures, and any of Lawrence's go for 3 to 400K range. Crazy money! Plus I had to buy British Standard Whitworth tools to do any work on it.

 

A few misconceptions that I would like to address.

Initiation of an arc is not dependent on amps. It depends on volts. The larger the gap, the more volts needed. If you calculate the air gap that 12v can jump, it's a fraction of a millimeter. Once an arc is started, however, the gap can be widened. How wide of a gap you can increase to is dependent on both volts and amps. If you've ever welded with car batteries, or seen someone do it, then you know that you need to touch the electrode (filler rod) to the grounded metal and draw it away in order to start the arc. If you've done any welding, especially with an inverter based setup, you know from experience that you can adjust how big of a gap the arc can be initiated over by adjusting the volts.

You can also calculate the temperature rise in a wire/fender/frame/etc if you can determine the highest resistance in that component and plug it into a formula with volts and current. That temperature rise changes as the resistance changes as the component changes temperature. It can get complicated, especially when you're dealing with components that don't have a known tested resistance and the path is variable.

If you do take the time to figure it out, or just look up some examples, you'll see that it doesn't take much current to heat up a component to the point where it can auto-ignite things next to it. A 250 amp or 300 amp fuse will allow more than enough current to catch things on fire.

Just look at your average gas oven or furnace and you can see that the electrical element used to ignite the gas does not consume anywhere near that much power.

If an arc occurred on the Carl's customer's car, it could have only happened in one of two ways:

1) There was a short to ground that heated up things enough to either melt away some of the metal making contact, thereby creating a gap; or, it caused a supporting item to melt and shift and create the gap.
2) A short to ground was caused by someone bumping/moving the wire and then removing that pressure and allowing an arc to be created.

More likely, there was never an arc, it was just a case of a short to ground heating things up enough to catch things on fire and melt some metal. In my experience, fire marshals and investigators are great at determining point of origin using their personal experience and training. But, they are very much out of their depth when it comes to the physics behind the causes of those fires. It's easy to take a point of origin and say that there should be a wire there, which is no longer there, and to then declare that it started with the wire. But it's an entirely different thing to get into the technical details of how that wire actually caused the fire or to even determine if it's possible for that wire and that power source to cause a fire. These same fire marshals are often called upon to give that very explanation, which they are not qualified to give, and so they produce answers that sound good to the layman and probably even to themselves. A 12v source initiating an arc in a static environment after hours of no movement? Technically possible. Practically a near impossibility.

I'm also a little surprised that no one has raised the one question that is most often asked on this forum when someone reports a problem with their car: What did you do last? Whatever you did last is probably related to the new problem that you have now. It seems very likely that the cause of the short was due to the work being done on the car as opposed to random and unfortunate timing of insulation failure.

Many many vehicle models are designed with large gauge wires running next to and even touching grounded metal components in cars. They rely on the insulation to protect them from grounding and on proper holding of the wire to prevent the wire from rubbing the insulation off through repeated movement.

As I said before, if you're trying to protect against a short to ground, you need to use a fuse with a high interrupt rating. MEGA fuses only have an interrupt rating of 2,000 amps. A car battery will usually be able to deliver that many amps in a short burst without any difficulty. That means that the MEGA fuse may actually fuse itself together if you have a short to ground of the main battery cable.

ANL fuses have a 5,000 amp interrupt rating. Which is much more likely to survive the situation that Carl's product is trying to protect against.

And since others are suggesting alternate products, which I avoided doing earlier, you can easily look for "ANL fuse blocks" and find many options that allow you to provide different fuse ratings for different feed wires. And, they usually come with an insulating cover so that the 12v connection posts can't be accidentally touched to ground. They come in lots of shapes and sizes. From compact 2-fuse in-line boxes to larger flat 4 or 8 way boxes to boxes with LEDs and volt meters that display current status.

And if you are intent on protecting against arcs, then you need an arc fault detection module designed for DC. Those are not cheap and very difficult to find with high current ratings.

I think that the single most important thing you can do has already been suggested several times on here....inspect your wires. Replace, repair or wrap anything that's even remotely suspect. Adjust where they run and how they are secured, if need be, in order to keep them from moving and rubbing through the insulation.

If you are intent on adding a fuse, use ANL fuses and a box with a cover. Preferably one that provides multiple fuses for the different feeds.

Someone has already provided some real world measured data on the current draw for the starter. Don't forget that you'll also need to account for the charging current from the alternator. If you factor those two things in, you can use an appropriately sized fuse and not just guess.

12v isn't much at all. It takes very little to prevent arc initiation. And very little to prevent a short to ground. Fuses at the battery are great extra insurance if sized properly. So is a fusible link. It's all about the sizing and placement of them.

Again...inspect the wires. That is the primary method of prevention. The fuses at the battery only come into play if you failed to inspect the wires properly and regularly.

 

Great conversation here. One element to consider is the fact that we have substandard quality wiring insulation on our cars. If the insulation is falling off of positive links in any circuit or locations, its not acceptable. Someone mentioned the well known wiring insulation problems from Mercedes Benz in the 80s and 90s. Wiring insulation does not HAVE to rot away over the decades. My 65 Alfa has a long under car positive cable run, clipped to the bottom of the car by bend over clips. This scared me a little when I rebuilt the car so I snaked the new battery cable through a long section of heater hose where it was exposed and clipped.

A more important takeaway to this post was the condition of the original battery cable I removed from the Alfa.... it had green corrosion in the strands on one end so it had to be replaced. When I pulled it out I flexed the hell out of the whole length of it and heard that awful crunching sound of rotted copper strands breaking up along the whole length of it. The insulation remained intact and flexible.. no cracking. This was a wire riding under a car for 50 years, soaked with oil, water, etc, a harsh enough environment to rot the copper in it, but the insulation was fine. If the Italians could source good wire insulation in the 60s, the Germans could/should have been able to do it in the 70s 80s and 90s. I recently did some engine harness work on a 79 308.. it was in good shape. Try that on a 79 928... you get crumbles of sh*t.

When old and un-shielded fuel hoses were burning our cars down the solution was to engineer new hoses with better materials (Thanks!) If an effective master fuse can be proven and developed that's great , but there's a lot of debate about its effectiveness here. Better replacement wiring for the constantly powered positive runs is the first step, with or without a fuse.

 

A set of Whitworth spanners must have cost you at the most about $10- you only need about 3 of them [5/16, 1/4 & 3/8th?]! Most of them probably have a metric equivalent- that or close to it

 

Many have suggested placement of high-quality shrink insulation over the wires that have broken or cracked insulation. Yes, if you can get to an end that will allow you to slide the shrink wrap tubing on. But sometimes, the cracks you want to add protection from are in the center of a long wire run, or the terminal on the end of the wire is too large to fit in the shrink sleeve.

For that, consider self-fusing silicone tape. I show it here to repair a broken connector boot, but it works great on wires. We have it in stock.

 

 

I don't, but I would be willing to order one up and let you know. I was kinda waiting to see what other suggestions popped up on this awesome thread before pulling the trigger.

 

The device the purple thing is connected to is a fuse set to go off in the event of an accident tied into the airbag system. If it goes off, it must be replaced, cannot be "reset".

Since our cars do not have the system to properly use that device, I would suggest finding something without such a fuse.

Why? For starters they will be smaller and in the event the fuse malfunctions (and they do) one less thing to troubleshoot. Yes it can be bypassed but that's wasting a lot of space. Other similar fuse / breaker boxes off other models will work the same for this intended purpose without that device & take up less space.

Video showing that device:




BMW's use a similar device:

 

Wow...Glad it all turned out ok in the end Carl.


My approach on my car will be to check the wiring in that area, as that is the root cause.

 

More I think about this, the more I realize we can solve this problem with 1 wire.

• Get a 12v 500a contactor.
• Put it in the battery compartment.
• Attach one terminal end to battery negative
• Attach the other terminal to the car's frame ground strap.
• Attach one end of the coil to battery negative
• Attach the other end of the coil to any 31 connection (switched +12v)
• Finally put a 10a fuse across the contactor terminals.

This solves your problem.

• The 10a fuse will support the key function and provide current to turn on the contactor.
• If there is a dead short when the car is off the 10a fuse will blow far before any arc or heating occurs (even on the smaller unfused lines to the ABS and such)
• If there is a dead short when the car is on, the battery voltage will drop, drop out the contactor, then blow the 10a fuse so it can't re-connect
• For true belt and suspenders fuse the ground line with a 300a fusable link.

The car will never be in danger from this failure again.

What am I missing here?

 

+1

While adding such a device isn't going to hurt anything, people need to remember circuit breakers can also fail, or not trip, or not be properly sized etc...... Houses burn down due to electrical fires all the time with circuit breakers failing to prevent them.

 

10 amps is is plenty to start a fire. See my earlier post. Even if it weren't, you would need to choose a fuse with an appropriate interrupt rating.

What you're really talking about is a remotely activated battery cut off switch. Although, maybe you also intended to leave power connected for the interior lights, trunk release, radio memory, etc?

There is no need to re-invent the wheel here. If you really want a fuse solution, get an ANL fuse block and select the size and style that suits your aesthetics and needs. There are a lot to choose from and plenty that will fit very nicely in the battery compartment.

If you're looking for something you can just assemble without having to add ends to cables, take a look at the Deka 00365 battery cable. It's about 10" long, 2 gauge, has a standard battery post clamp on one end and an eyelet on the other end. Then, get a battery post to stud adapter. There are lots to choose from that will screw right onto an ANL fuse terminal.

Or, have a local wiring store or online supplier make up some cables exactly how you want them. It's very easy to do yourself, and cheap to pay someone else to make them.

A few bucks, and you'll have a very elegantly executed fuse block at the battery.

But, the real protection comes from inspecting your battery lines and repairing/replacing them as needed.

 

To protect against battery current causing an issue the placement of a fuse immediately on the positive or negative side of the battery makes no difference (Though the negative side may be easier) - they will provide equivalent protection.

However note that when the car is running the current supply normally comes from the alternator and the battery is a net consumer of current as it recharges. Under running conditions a fault could still take out a battery fuse (in either position) - but since there is no fuse for the alternator - it will continue to provide power to the rest of the car as long as the engine is rotating. So certainly under running conditions the situation is more complex.

I'm not really a big fan of a master battery fuse. However after the battery to starter connection - fusing all the smaller feeders makes sense, as do fuses at the battery for the smaller feeders (for: ABS ,PSD, ECUs, Cooling fans). Small feeder fuses at the battery are easy enough to implement - but fuses at the starter end of the main feeder have no obvious place to go - and even if there were one it would still be a most inconvenient place to access...

Also appropriately fusing the feeder to the jump post means you can't use it as an actual jump post anymore - but you could always just fuse the downstream feeders to the CE panel. Given this there are always some key connections that must just be maintained in good safe condition (for safety and reliability).

Physical implementation on primary power wiring is always a challenge - if it isn't implemented very well - it creates potentially more risk issues (reliability & safety) than it solves.

Alan

 

The master of all things tegarding 928 electrical has spoken.