WD B40 Fuse

[odbsmith]

Thanks V500. Its sod's law ...you look everywhere, post query on forum .... and then find it 30 minutes later!
!!

[limeyrob]

The 35A glass fuse was the standard for every vehicle from the 30's to the 60s  and most cars would get by with one or two. I suspect one is fitted to the new harness as it is the correct "in period" part and will do the job.  I've honestly no idea what a 35A glass fuse blows at but I'll bet its well over 35A if its a sudden surge since I've had wiring fires with the fuse intact.
I make my own harnesses and include a few changes for safety or usability.  One of the hardest issues is what to fuse and why. There are good reasons not to fuse the ignition circuit for example, you don't want a blown bulb to cut the engine while you are at speed.  I've recently gone over to all LED bulbs including my DIY indicators on the A10. This brings the current down a lot so I have fused the A10 with indicators at 20A and this seems more than enough. Horns are often not fused, they draw a lot of current and taking your hand off the button should stop the problem.

[V500]

Indicators at 20A will see melted wires before the fuse even thinks of blowing.
The old standard 35A glass cartridge fuses will see most cables glowing like electric fires before it blows. The descrimination of those old fuses was so coarse that it probably took 45 or even 50A to blow it. BSA etc only fitted them to show how modern and up-to-date they were compared to the Japanese competition, but then they didn't want any chance of them blowing and more dealer returns and warranty claims.
Most old bikes will need the electronic reg fused (as recommended in the paperwork), the electronic ignition (if fitted) also, and an 8A or 10A fuse in the battery earth line.
The old "add up all the load and then choose a fuse above the total" as mentioned in the thread above couldn't be more wrong.

[limeyrob]

My posts reads wrong, the indicators draw under and amp as they are home made LED ones, its the whole bike that fused 20A on the main battery cable and I think that's too much so I'll probably drop that to 10 or 15.  Sorry for the confusion.

[Novocastrian]

Some interesting comments on fuses (and the usual smattering of mis-information thrown in).  I was the Sales Manager for Littelfuse (yes that is the correct spelling) and we invented the ATO blade fuse, which is the fuse I would recommend for your automotive applications.  The old "Lucas" 1 inch glass cartridge was indeed labelled at the "blow" rating rather than the rating it was designed to accommodate but I assure you a genuine Littelfuse fuse (which we manufactured at Washington, Tyne & Wear and marked LF) would not get to 45 or 50 amps as suggested.  However,  there were (maybe still are) fuses manufactured elsewhere of dubious quality that would operate nowhere near their designated current rating. You might as well use a nail; we had some fun testing some of these cheapo "fuses".  If you buy cheap autojumble stall fuses or cheap eBay fuses, then more fool you.

We manufactured our ATO blade fuses in Switzerland and believe me,  the quality controls and testing were stringent. I believe Littelfuse now manufacture elsewhere but you can be sure of the quality.

Also, bear in mind there are/were similar USA made glass cartridge fuses which were 1.25 inches but were labelled differently.

The ATO blade fuses (and Mini & Micro fuse equivalents) made by Littelfuse, Pacific and Bussman are all fast-acting and excellent quality.  Fuses which have no manufacturer's markings should be avoided unless you like gambling.

[Novocastrian]

Worth a watch....

https://youtu.be/nELwmfAOz_I?si=-DYrrqjXNmfP7MIK

[Rog1]

Whatever fuse rating you decide don't use an inline fuseholder; they are unreliable. Better to use blade fuse holders. Then as Novocastrian says, fit a good quality fuse. Blade fuses are also more readily available if you have a problem miles from home.



 

[limeyrob]

If you go down the blade fuse route (I have) you can get mini resetalbe circuit breakers that fit a blade fuse holder.  They are about £6 and while I can'y vouch for their accuracy they are really handy for fault finding since you can just keep resetting it until you find the short and great if you are out on the road.

[Rog1]

Worth a watch....

https://youtu.be/nELwmfAOz_I?si=-DYrrqjXNmfP7MIK

It certainly was worth a watch! Thank you.