Fuses

[TTM]

Good afternoon,

Is someone fluent with the fuse box on Aces?

The handbook says there should be 2x 25 amp fuses and 2x 50 amp fuses, which "can be readily identified by referring to the wiring diagram", except the W29340A wiring diagram that I have does not mention the amperage of the fuses illustrated.

Perhaps one with basic electrical knowledge and understanding would guess just by looking at the corresponding functions, but this is sadly not my case. For some reason the 4th fuse on the diagram is not linked to any electrical component anyway, whilst it does serve a purpose on my Ace, which goes in line with the mention of 4 fuses in use according to the handbook.

The handbook also mentions 2 spare fuses, but I do not have them and ignore where they should be mounted as there does not seem to be any extra room for these two in the fuse box.

[TTM]

Further analysis with a multimeter has allowed to identify the function(s) of each fuse. The extra fuses also most likely sit in the two round slots moulded in the base of the fuse box.

I still do not understand however why 50 amp fuses may be used for functions that most likely do not draw that level of current.
If we consider that the headlights on full beam perhaps draw the most current in the whole system, then perhaps they won't need more than 30 amp?

[3280]

Don't forget that the original fuse ratings are about double what the stated rating is on a modern fuse!
This gives a good layman's explanation, albeit with a transatlantic viewpoint
https://mossmotoring.com/moss-tech-101-dont-blow-a-fuse-over-your-fuses/

[TTM]

Thank you for your interest. The headlights were a bad example actually as their circuit does without a fuse.
I suppose I will have to try several combinations then.

Side question - Is it normal for the front side lights to stay on when turning on the mains?

[B.P.Bird]

Thomas,
Front and rear sidelights are on the same circuit (red wires) therefore the fronts have to remain on to keep the tail lights lit.
Barrie

[TTM]

Barrie, thank you for the confirmation.

[James Eastwood]

Confirmed  :)

[TTM]

Thank you, James.

[B.P.Bird]

Thomas,
Did you reach a conclusion on fuse values ? I think the Lucas cartridge fuses on my Aceca Bristol, BE 668,  were 30 amp and 15 amp.
Barrie

[TTM]

Barrie,

I have only driven the car once, this morning, since posting this topic, and I have only been able to notice so far that 4x 35 Amp fuses seem to be doing well. Hardly a scientific conclusion though...

[TTM]

Good morning,

Well, exactly during a few spirited laps at Le Mans the 35 Amp fuse that handles, on my Ace at least, the horn and the warning lights melted. I seem to remember this happened in the past already, so what size fuse should I try in there? Since the handbook mentions 2x 25A and 2x 50A fuses, logic dictates I should try a 50A?

[AC Ace Bristol]

.
TTM ???
RE:Fuses for Ace Bristol.
1.  ..  ..  ..  Turn Lamps and Brake Lights........................25Amp
2.  ..  ..  ..  Wiper, Fuel guage .......................................25Amp
3.  ..  ..  ..   Horns .......................................................50Amp
4.  ..  ..  ..   side lights  ................................................30Amp

Details taken direct from my wiring diagram which was personalised by previous owner in USA pre 2000.
Hopefully this information might help.  ..
You have a few Good AC guys in the Club car park and at the two Chateau, they should be able to assist. 
Good Luck.

Keith

[TTM]

Thank you Keith. I replaced the offending fuse with a 50A unit. Let's see if it holds together. Still surprised how the 35A could have melted as it's not like the horns are being used continually.