Jupiter Fuse ratings

[Bronteboxer]

Can anybody tell me the correct rates (or best practice) for the Jupiter fuses please.

It’s the fuse which is in circuit for the brake lights/fuel gauge, I’m particularly interested in. I can’t find any clear notes on here and the manual seems to suggest 2 35amps. I have a 15 amp in currently and 35amp seems very heavy for what it’s protecting. I don’t want to overdo it and end up with burned out wiring or worse!

Thanks in anticipation.

[Keith Clements]

Yes 2 x 35A but it depends what you have in circuit. If original filament lamps have been replaced by halogen or LED or if you have electric cooling fan or fog lights then this will alter fuse ratings.
The horns do not go through the fuses in the regulator but a separate one. They take 20 A.
https://jowett.net/forum/download/file. ... &mode=view

You may be interested in the way my Jup is fused.
https://jowett.net/forum/download/file. ... &mode=view

[Bronteboxer]

Thanks Keith. I have the wiring diagram, but there were no ratings marked just in the Manual. I note you have 5 amp on the brake/fuel fuses. I don’t have anything extra going through that circuit and they are Standard stop/side bulbs. When I rewired it 27 years ago, I did it Standard and have not altered.it.

Why is it such a heavy rating - 35amp! for a fuel sender, gauge and two brake lights? In your revised circuit and fusing you have 2 @ 5 amp?

I’ve been running mine with a 15amp fuse, but on replacing the brake bulbs today it’s blown and and having done tests, I can’t find a short, so hence the question as I revisited the manual to check the factory rating. It’s so long since I put the fuses in I forgot what I put in etc. I think I must have just installed what I though was right at the time and automatically replaced the same as time has gone on.

I have to say I am a bit concerned about 35amp. I can’t get my head around it, hence the question do you know why it’s such a high rating?

[Keith Clements]

I used an ammeter to test what everything took. If a 15 A is blowing I would check for a short. I reckon you put the wrong bullb, in or the wrong way round or shorted the socket.

[Bronteboxer]

Thanks for the advice. Much appreciated.

Correct bulb, in the right way round. Been through it and no short. Traced back to brake switch and fuse. So back to the drawing board tomorrow.

[Keith Clements]

The rule for fusing is that the current carrying capacity of the thinness wire in the circuit governs the fuse capacity. Fuses also come in various types such as slow and fast blow for different types of load and protection.
On Jupiters you can get unusual situation as poor earths are common. Thus a poor earth on engine or regulator can blow any component..

[Bronteboxer]

Problem solved. Intermittent issue with bulb holder.

I have now reduced the fuse rated at 35amp in the manual to 10amp & everything is OK.

[Keith Clements]

Yep shorting socket!