6 replies to this topic

[Bat]

Hi,

As the electrical and electronic systems get more involved with newer Minis and they're now getting to the age they become troublesome I thought I'd try to help out.

 

Sooo, useful tips.

 

1 ... A test light is more useful than a multimeter for general testing.

Why? Simply, the bulb in the test light will apply some load to the wire and show up poor connections. Multimeters are best used for electronics rather than electrics.

You can get a false 12v reading from a multimeter, it will show 12v with the poorest of connections down the line.

In this common situation a test light will not illuminate! This will save you hours of chasing around for a fault.

 

2 ... Fuse boxes are common problems on Minis and the inline fuses more so.

First things first, check the fuse! Check for fractures in the fuse itself and corrosion.

Then remove the fuses and check the connections in the fuse box, both the ones that touch the fuse and all the wires that plug on to them.

In-line fuse holders, don't be afraid to give the wires a tug first. They won't come out if the connection is any good, if they do there's your problem!

 

3 ... The ground or earth side of the system is 50% of it and just as important!

Because we use the car body as the earth, there's not loads of black wires running everywhere, people tend to forget all circuits need a good return to the battery to work properly.

When cleaning up an earth connection like the one in the engine bay on an MPI, don't just clean where it bolts on, undo the plug too and clean in there, it will be just as green as the rest of it!

 

4 ... Wiring diagrams.

Download them and take a look before you have a problem. At least then you'll have some idea of what you're looking at, they're not difficult to follow, just like those puzzles on the happy meal sheets! 

Find the item your having a problem with and follow the lines to see where they take you. Remember everything starts and goes back to the battery.

 

5 ... Charging and starting problems.

As alluded to earlier the battery is a key item, here more so as lots more power is involved.

It takes 100-150amps to crank over a standard mini engine, that's a lot of power. 

Start at the beginning, put your headlights on and then crank the engine over.

If the lights go dim your battery is flat.

If everything goes off and doesn't come back on you've got a poor connection!

These aren't cast iron rules there's always the odd balls!

You'll need a good battery to check the charging, if the battery is knackered it will hold the voltage down making you think the alternator is at fault.

With the system under load, keep those headlights on, you can use your multimeter to check for volt drops.

This term is used to describe different voltages in different parts of the system caused by bad wiring or poor connections. You should have no more than 0.2v difference between what you measure at the alternator and what's at the battery.

Remember the problem could be the positive or the ground side so check both!

 

Hopefully we can get this pinned and people will look here first so they can provide more information when asking for help.

Cheers 

Edited by Bat, 27 July 2018 - 01:02 PM.

[Spider]

If I can add to Bat's checklist here, I'll add that experience helps too and with electrical fault finding, sometimes you need to think backwards as well, eg, the switches in some circuits, don't always switch the live side, some switch the Earth (Oil Pressure lamp for one comes to mind) and some circuits work by bringing voltages on both sides of lamps up to the 'live' voltage to extinguish the lamp (like the Charge Warning Lamp).

 

Also, in regards to studying circuits, which they can be handy, sometimes they can be confusing too. I'd suggest learning what the colours of wires do, they all follow a pattern or code. Off hand I think there was a change in the standards in the 80's , however, as an example, prior to that when the cars only had 2 fuses, if the wire was a solid colour, it was a live feed, and depending on the colour, will indicate from what source, eg, Brown is direct from the Battery, while Green is an Ignition Switched feed via a Fuse.

 

The wires with Trace colours indicate they are after a 'device' which could be a switch or a lamp, eg, Green / Red is Left Indicator (as it is after the Indicator Switch) and White / Brown is the Oil Pressure Warning Lamp (as it is after the Lamp). 

 

I feel this approach helps cut through some of the confusion of the diagrams.

 

If you do need to follow a diagram, sometimes drawing your own circuit from the main diagrams helps, however, just draw out that part of the circuit you're having trouble with, then the page is much cleaner.

 

And, lastly, don't forget we do have Colour Drawings that Mike has has done and kindly shared;-

 

http://www.theminifo...agrams-redrawn/

[Ethel]

I don't think wiring colours changed for Minis. They just gained a few as they got more complex.

 

Black means earth, as a trace colour it can signify it feeds a component that earths e.g. from the ignition coil to the dizzy, the horn and interior light door switches.

 

Brown is unfused permanent live

Purple is fused permanent live

White is unfused live with the ignition on

Green is fused ign on

 

I'm not sure if the full list isn't already on the forum. It's certainly online

 

Thinking about it, you could make a "family tree" style diagram.

[Bat]

Hi,

Yes, the main colour does denote it's "source" if you like and the tracer or stripe down it is a secondary piece of information.

Base colours, the main colour of the wires...

 

Brown ... Direct from battery, usually feeds the fuse box, alternator , ignition and main light switches.

 

Purple ... Fused permanent supply, always on protected by a fuse, powers interior light and horn.

 

White ... Ignition switched supply. Only works with key in number 2 position. Feeds the fuse box, ignition coil and instrument cluster.

 

Green ... Fused ignition supply, protected by a fuse. Feeds reverse and brake light switches, flasher unit, wipers.

 

Red ... Side lights. This comes from the light switch in the switch panel in first and second position, often there's an inline fuse on the bulkhead for sidelights.

 

Blue ... Main lights. This feed comes from the light switch in the switch panel when in headlight position. It feeds the dip/main switch and fog light switch.

 

I've not given an exhaustive list of what each colour does just the main things that come straight to mind...

 

To give a practical example...

You switch the ignition on, the white wire goes live. This feeds the fuse giving power to the green wire.
This green wire, of which there's more than one, goes to the reverse light switch.
You put the car in reverse which then powers the green/brown wire going to the bulbs.

 

So there's 2 wires to the reverse switch, a plain green wire and a green with a brown stripe.

If you have a faulty reverse switch you could join those 2 colours together instead of using the switch to test the rest of the wiring, bulbs and holders and not forgetting the grounds!

 

Cheers

Edited by Bat, 28 July 2018 - 10:18 AM.

[KernowCooper]

@Bat A test light is more useful than a multimeter for general testing.

 

Sorry mate have to disagree, if all you have is a test light its better than nothing, but its a one trick pony, where as a multimeter can tell you so much more. The bulb is ok to confirm a circuit, perhaps I'm biased

[Bat]

Hi,

A test light may look like it only does one thing, but it's the fact that it loads the circuit that is much more useful than an multimeter.

A multimeter is designed not to put any load on a circuit so it won't damage delicate electronic devices.

Many posts I've replied to recently people have been caught out by poor/weak/corroded connections where a multimeter has shown 12v and they've gone round the houses only to find a poor connection to where they thought they had 12v.

I've done it myself at work in the past. I now think of it as "meter to measure, test light to test"

You don't need to know the voltage, only that you have power where you're testing. 

As a side note I've got an led test light that I use when I don't want a load on a circuit so I can quickly test wires in electronic systems without fear of damage.

 

Moving on from that, there are many tests you can carry out with a test light and a bit of adaptation.

I'll explain in the next post...

Cheers 

Edited by Bat, 03 August 2018 - 06:46 AM.

[Bat]

Hi,

Test light Vs multimeter...

We all know what a multimeter does as that's what everyone uses.

It's got to be the best, it's got a digital display, does many things, right?

Not really, especially in the case of a Mini, it's all old school stuff in a Mini.

Rover are well known for using the same thing from 1950-something for as long as possible, the basic electrical systems are no different.

Lights, wipers, heater, indicators, instruments it's all designs that were around before your grandad!

 

I've mentioned in the first post how the test light is a better tool in fault finding situations.

So does that bulb and a bit of wire just do one thing, or is there more to it than meets the eye 

 

I think you may be surprised...

 

First things first, put your test light across the battery.

Here, check it lights up. Wiggle the wire about make sure it stays lit up. Also make a mental note of how bright it is.

Tests you can use it for could be...

 

Testing for a short .. Difficult thing to find those short circuits! The term "short-circuit" means exactly what it says, the electricity is finding its way back to ground through a shorter path than it should, causing excessive current to be drawn and blowing your fuse.

 

Blowing fuses straight away? 

Hook your friend the test light up to replace that fuse, use bits of wire or a small screwdriver to connect it in place of the fuse itself. Switch the ignition on if you need to...

So now your test light is lit up, you're thinking 'well it's going to do that there's 12 volts going to that fuse!'

Yes, but where's the ground for the test light coming from? 

It's coming from the short in the circuit, so what you're aiming to do is get the test light to go out!

Disconnect wires from the fuse holder, one at a time, lets say they're green. Check the test light each time, when it goes off you have found the problem circuit. Now put the fuse back and see what doesn't work, what doesn't work is where your short lies.

 

What if your reverse lights aren't working now for instance?

Connect the test light to the fuse and to the wire you disconnected, it will now light up again.

Find the first thing in the circuit, using your grey matter or the wiring diagram, it's the switch.

Unplug the switch, check the wires aren't rubbed bare or melted to that big bore exhaust you fitted last week!

Test light still lit up? Then it's got to be a short between the fuse box and the switch.

 

At this point there's 2 ways to carry out a repair, just run a new wire from the fuse box to the switch or pull the car apart and find the problem and repair just a section of wire. 

If you voted for option 2 leave the test light where it is and move the wiring loom around an area at a time until the bulb goes out, now you know where the short is! 

 

I'll come back to this later, there's more 

Edited by Bat, 03 August 2018 - 08:23 AM.