Wiring Diagrams

[patrickhowell]

My recently acquired Lomax has a complex wiring system, with seven fuse boxes and 24 fuses in all. These are 3,5,10,15 and 20amp. Unfortunately, a previous owner passed on without leaving a wiring diagram, or labelling the fuses. While I have been able to work out some of the circuits, which were done in a professional manner, it would help to know what type of fuse suits what type of application. 3 amp is obviously for light loads, and 20 amp for heavy, but no one on Google seems to give their type of application, e.g. lights, horn etc. Can anyone help?

[administrator]

The easiest way of determining what fuses do what, are to remove them one-by-one and observe what's not working any more.

Obviously, the bigger loads will need the bigger fuses, so headlamps and hazard warning lights probably draw the most current.

The starter and ignition circuit are not fused typically (certainly not the starter)

Rgrds
C

[llanigraham]

You're lucky. Mine has a 4 fuse board but only 2 of them appear to be "live".
I've got a winter project to rewire it!

[patrickhowell]

C
That's logical, but would not tell me if a particular application was appropriately fused, hence my general question
as to what fuse ratings are suitable for what applications?

[administrator]

Hi,
It all depends on what circuits are combined.

For the lighting circuits, you can determine the current draw form the wattage of the bulbs. So if you remove a fuse and the indicators stop working, then you calculate the required fuse by determining the wattage of the bulbs that are affected and diving by the voltage.

Another way of doing it would be to connect an ampmeter across the fuse terminal and read the current draw. This is going to be tricky though, as initially the currently draw will be high and drop back - something that a slow-blow fuse can cope with.

As your car has a very 'bespoke' wiring arrangement, it will almost certainly be easier to use the 'remove a fuse' method to map out what fuse controls what, and then try to determine current draw. This will be easy enough when it comes to bulbs - whose wattage is clearly understood, but tricky when it comes to things like gauges and wiper motors etc.

I don't think anyone will be able to give you a definitive answer - it's all down to which components are combined in which circuits in your particular car.

Rgrds
C

[howardjs]

Hi, Yes Callum is absolutely correct. There is no way of knowing how many loads are on a particular fuse without pulling each one in turn to see what stops working. It may be for example that all side lights are on one fuse or the front and rear may be on separate fuses. Or the indicators could be separate left and right or all together with the hazard circuit.
For example if they are all together then 4 indicators at 21W + 2 side repeaters at 5W makes 94Watts /12 volts = 7.83Amps. In this case a 10 amp fuse would probably be chosen, presuming that standard filament bulbs are used. (I have since changed to LED bulbs and need to update my fuse ratings).
Anyway at the risk of inviting criticism and ridicule here is the circuit of my car showing the fuse ratings for each load, it's been in use for 8 years with no problems so far. The "control box" contains a line of relays and fuses with some CEMOS logic to sort out the indicator flashing and hazards also the wiper motor control.
Howard

[patrickhowell]

Thanks, chaps, that's most helpful