Talk Morgan Forums Morgan Sports Cars Maintenance & Servicing Early +8 fuses

Thanks Graham, but the early +8s aren't quite like that. The fuse for the horns and radiator fan (through a relay) is fed from the ammeter. Two other fuses are fed from the ignition switch, and the fourth between the lighting switch and the connected lights and spotlights. The pre-engaged starter solenoid (mounted on the starter) has the battery +ve connected directly to it and also 4 other brown wires going round the car. So a single power fuse will not work without a major rewire.

Arwyn - yes, four glass fuses and two spares, but I doubt all all 25 A.

Hi Francis, I applaud your wish to maintain a degree of originality and may be a much simpler task where the manufacturing techniques were somewhat more..err..uniform than they may have been at the MMC...? Over the years I have observed all sorts of attempts to relate Morgan wiring diagrams to Morgans with issues resulting in a measure of frustration. My +8 Morgan was built in the mid 80`s and the wiring diagram in the handbook does not match that which can be found in the car, not counting wiring alterations of course.

I guess with everything switched on it might be possible to measure the current draw across each of the fuses them being removed and an ammeter put in circuit in place for each test..?

With a bit of luck the colours of the wires should guide you towards the components in each circuit to give you an idea of the normal current draw...?

https://www.gomog.com/allmorgan/LucasColours.html

Good luck.

The horn being wired outside the ammeter circuit (although often connected for convenience to it's battery side) seemed to be common practice in the 60's and 70's and maybe earlier, for both cars and motorcycles. Handy on my Velocette and Land Rover as the ammeter records the compensating positive current back towards the battery when horn is operated, proving dynamo is working.

Having all the brown positive feeds from the pre-engaged starter terminal makes sense as ideally the main positive battery cable runs directly to it.

Be aware of the differences in fuse ratings, Francis. I believe that the early Lucas fuses are rated at the current (ie. 15A) at which they would blow immediately. North American and I think most modern fuses are rated at the maximum current that they will support indefinitely without blowing. Two very different situations, with a Lucas fuse blowing at approximately 1/2 the current of the NA standard. For a period Lucas fuses carried a dual rating, reflecting both circumstances. I found this out to my cost due to a previous owner replacing the original Lucas fuses with similarly rated NA replacements. A subsequent short circuit resulted in the car attempting to immolate itself.

I think the point that Graham made earlier was that any brown wires (in his photo just 2 but in your case 4) emanating from the starter solenoid need to be protected by a suitable fuse before they reach their own respective fuses. If those brown wires should short to earth the battery will feed an enormous quantity of energy in prior to exploding or the wires burning out!

The problem is Doug where do you draw the line. Adding fuses in series with existing fuses not only causes minor volt drops dependant on current flowing through them, but far worse it adds unreliability, connections loosening etc. The fuse is there to protect the equipment it's feeding and the cable to it. Better though that effort is put into good mechanical installation with the heavier gauge cables leading to the fuse box in a clean dry location as with normal automotive practice.

There is a case on a long cable run where current can flow either way, being fused at each end but I can't think of a situation on a car that would qualify for such.

[/quote Luddite] Over the years I have observed all sorts of attempts to relate Morgan wiring diagrams to Morgans with issues resulting in a measure of frustration. My +8 Morgan was built in the mid 80`s and the wiring diagram in the handbook does not match that which can be found in the car, not counting wiring alterations of course.

.[/quote]

The GoMog wiring diagram labelled "...4/4 AND +8 1969-73" does not wholly accord with my December 1973 +8 Mog. Firstly, there is an error in the diagram; the feed from the hazard flasher should not go to terminal 6 of the flasher switch, but rather to terminal 5. Secondly, my +8 had a two pin flasher unit, not three as shown. Thirdly, my hazard switch does not have the functionality shown in the GoMog diagram; rather it is a two pole change-over switch with the two poles commoned in the middle. And I haven't managed to work out how the dash hazard warning light works (it does!) with a two pole flasher unit, but not when the indicators are used.


[/quote] I guess with everything switched on it might be possible to measure the current draw across each of the fuses them being removed and an ammeter put in circuit in place for each test..?[/quote]

Nice idea, Luddite. I'll try it this weekend, but bearing in mind Bloggins helpful comments on fuse ratings.

Francis

I suspect that the webmaster at GoMoG does his best to provide as much information on Morgans as may be humanly possible in the hope of helping those trying to keep their Morgans on the road, but if the MMC can not supply a handbook with an accurate wiring diagram for a Morgan at the time it was new, I suspect some time down the road folk are bound to be scratching their head trying to resolve wiring issues...? (-:

I suspect that around the time your Morgan was built it would incorporate standard Lucas components which can be found in use in many other UK manufactured vehicles of the same era, thus with a bit of searching you may find circuit layouts for those components on MG or Land Rover Forums and the like...?

http://www.advanceautowire.com/mgb.pdf

As for fuse ratings that is perhaps a tad more complex than imagined to work out what any fuse will blow at and involves a bit of mathematics to fully understand. I bow to Bloggins knowledge of fusing factor variations relative to differences between the UK and US, for I have no such knowledge, though do have a measure of understanding of fuses with a dual rating in industrial circuits and which carry an identification as being "M" rated for electric motors, given a motor can take circa seven times the normal running current at start up, before an electric motor gets up to speed and the current drops to normal... Wire fuses are pretty coarse means of protecting wiring and generally identified relative to the normal current draw expected in the circuit, but it can take many more amps than the stated rating for the fuse to actually blow., it can all get rather technical requiring both time and current to be factored into an equation....Yeah it can all get a bit scientific, when all that is required is to select the correct fuse for a circuit

https://en.wikipedia.org/wiki/Fuse_(automotive)

Perhaps best to be sure you understand the likely current to be found in a circuit before attaching an ammeter across the fuse holder for you could easily blow a meter circuit if it is not capable of carrying the current likely to be found at that location..

There are those better qualified than I who may be of far more assistance to you but happy to ramble on a bit if you think it might help.

Good luck.

The factory handbook that came with my 1985 4/4 TC states:-
Holder marked 1 & 2 = Lights = 35amp
3 & 4= Horn & headlamp flasher =35amp
5 & 6 = Ignition =2amp
7 & 8 =Wipers, washers, brake lights
Spare fuses both 35amp.

I presume 35amp refers to the old Lucas glass fuses marked 35/17amp

However, the wiring diagram in the handbook is different to the actual wiring in my (low mileage original) car!.