Auto Electrics - General fuse Guide?

G'day Guys/Gals

I have a question for all you Auto Electric Gurus out there??

About a month ago Dasdubber and I neated all the wiring of my KG and replaced the old ceramic style Fuse Blocks with a new style Push Pin Blocks, we pretty much kept all connects as they were just rationalised where wires ran, neatend everything up etc.

We have also added a couple of new lines for gauges, oil cooler fan, fuel pump etc.

Long Story Short my question is this....

Is there a general rule of thumb for what amp fuse you should use for each element???

i.e lights on 15amp, guages on 5 amp etc

The original wiring was all over the place so assuming I should replace fuses with what was there previously could cause problems.

Advice would be most appreciated.

Cheers

Brad

Fuses should be rated above the normal operating current of the device and below the rating of the wiring. This can be tricky on old dubs as they often have several devices on each fuse.

The exact fuse size will depend on the rating of your lights, but for a standard 55/60W head light
60/12=5amps on high beam. So two headlights on high beam = 10amps, my type 3 has a 16amp fuse for high beams. You need a bit extra to prevent nuisance fuse blowing.

Check the power rating of the fan motor and fuel pump, as these may suck some juice. Be aware also that fans can suck upto twice their rated power on start up. Depending on how you have connected everything up, it would be better to run the cooler fan direct from the battery and use an inline fuse, rather than running it through the fuse box.

use this as a guide from www.vintagebus.com

It is the late fuse box off a 1979 beetle.

Hmmm..........just looked at it

16 Amps interior light?? :duh

I did say use it as a guide 🤓

You are pretty safe using a 10 or 15 ampere fuse as these will blow very easily with a short circuit...
20 amperes blow very easily too...

I do have some 50 ampere fuses which will never be used.
A Mechanic I used to work with many years ago used to use them for tractors with a fuse blowing problem....

Now these do take a bit of blowing.... and if light duty wiring was used... the wire would burn up instead....
very dangerous....

16 ampere fuses blow very easily.... too...

Lee

Thanks Guys

Will have a look again tonight.

Everything was working OK after the rewiring, but over weekend have dropped 1600 out to replace with 2110.

I don't remember touching the lighting wires and now every time I put the lights on the fuse blows, maybe due to tiredness I forgot I did touch the wires and now its just shorting somewhere.

Brad

Could you have caught the rear lights or number plate light wires some where??

Well that means the fusebox IS working...

it doesn't take much to make a short circuit....

Best of Luck...

Lee

Circuit breakers- push to reset, save lots of time and stuffing about.

Scratching my old physics study days, amps=volts / watts

so 100 watt lights x2 in a 12 volt = 16.6 amps

This may be why you are popping them.

If you take all the globes out and reconnect them one by one until the fuse blows you will find the culprit.

Dont up the fuse without investigating the load on the wires, I would hate to see your beautiful KG go up in smoke (unless its from the tyres!)

luck mate, happy to help if you need

kkk

Thanks guys

kkk - lets assume I may not be as up to date as one can be, when you mention "investigating the load on the wires: what exactly do you mean and how do I check this - I'm assuming a multimeter???? Once you have the load how do I ensure I have the right wire for the load etc.

cheers

Brad

You can measure the load with a multimeter when operating,. Only problem is to measure current you need to put the multimeter in series. So you have to disconnect the wire form the device and insert the multimeter. Just check the max power rating of your multimeter. The other way is to use the nominal power consumptionof the device. Like KKK said, 100W ~ 8.4Amps. Gauges use very little, where as spotlights and electric motors can use alot.

There is a standard maximum load (ie amps) depending on wire cross sectional area (ie diameter). See here http://www.powerstream.com/Wire_Size.htm.
Did you replace the wires, or just tidy up the old ones? If you look at new auto wire, it is all rated according to amps and generally comes in certain set sizes eg 5Amp, 8Amp, 10Amp, 15Amp etc. My Bentley service manual lists all the wire sizes on the wiring diagrams in square mm. You can use this to work out the max power rating for any given wire.

Hope this helps.