15 replies to this topic

[A362 TTU]

Seen as my mini is off the road while I am at university (at least 2 more years) and I dont have much cash to spend on it I have moved my focus onto other projects related to the car.

The wiring loom in my car is functional, but a little hacked up and botched. I also feel that the original design can be improved upon (e.g. seperate fuses for each circuit, move fusebox out of engine bay, tidy up routing etc).

So I am going to try and design a new loom, tailored specifically to my car (e.g. It will 'natively' support my extra spotlights). My electronics knowledge is limited to a GCSE on the subject hence why I am looking for some further help with my design.

Right now I just want to make the diagram. Once that Is complete I will determine the gauges required for each wire and then where it will be routed in the car.

So here Is a basic look at my plan:

The idea is to have 3 interior fuse boxes, for constant, accessory and ignition circuits fed by a clean line straight from the battery, the accessory and ignition fuseboxes would become live when the relays are activated by a feed from the ignition barrel.

Am I along the right lines? do you have any suggestions? (Im also interested in any circuit improvements and where to put them - (e.g. kill switches to stop the car from starting but allow the starter to crank, so it isnt obvious its a kill switch)

Once I feel that I am on the right track I will draw up every circuit properly .

If I complete this design I will likely implement it.

[MRA]

Obviously there are a few components missing, however the idea of a "kill" switch to prevent the engine from starting can be acheived by inputting it into the ignition circuit, thus the engine will turn over but will not start.

Once you have the circuit diagram, you will need to produce a "power" diagram, ie power consumption for each item, this will allow you to apply circuit balancing and correct fusing strategies, also think caredfully about your fuse box MTA do some pretty good units but they are not cheap, I am using an Early S type Jaguar fuse box in my Mini, the unit is made by a company called Yazaki, don't go for the newer rounded version as it is a pain.

Best bet is to get one form a breakers and use PIDG crimps with glue lined heat shrink to seal.

But whatever you do do not solder as this very bad, as solder will wick up the wire circuits causing fatigue failures and make sure that you use the correct tools,I have seen loads of good intentions ruined by poor tooling.

What software are you using for this project ? is that Visio ?

[lrostoke]

I think something mentioned before as been fuses on headlights, you use 1 fuse if it blows your in complete darkness...its best if fused to have separate for each side, which means 4 fuses when you include main beam and dipped

[MRA]

Yes each lamp unit would be requiring a seperate fuse and also a seperate ground point, not just seperate ground wire, but multiple grounding points to stop Back EMF, voltage going "up" the "down" route.

Alongside the power chart you will also need a grounding strategy.

and if you are using a relay for individual areas you will very rapidly run out of "current" room i.e. most relais will not function very long if you pull more than 30 may be 40 Amperes max

The method used is to remove the relais and fit buss bars, most modern fuse boxes will have buss bars that are either a solid bar with terminals stamped as a single part or a "multicrimp with 3 wires (max) one side and a feed wire the other side or a crimp specially made with a number of terminals one side and a circuit feed the other.

Edited by mra-minis.co.uk, 01 April 2013 - 01:10 AM.
Updates in Red.

[lrostoke]

No **** Sherlock :) but only one is showing for lights ;)

[MRA]

No **** Sherlock :) but only one is showing for lights ;)

Sorry chap, I editted my mistake out I was hoping that i got in before you saw the error ;-(

[lrostoke]

No worries, I guess the big danger is over complicating..Can't really say there was much wrong with my 1984 loom all worked, just I shorted a main power feed a few years ago and it melted the loom..only reason I rewired mine really..

[MRA]

I added an ECU, with launch and traction control and 2 sets of spots, no radio though as the SCCR box is enough music to my ears. I then rewired the whole lot in about 1999, 2000 I applied the hierarchial logic to the wiring harness and never had any issues, if one lamp went out I still had plenty of other lighting

[Dan]

There is no point, and it will use a huge amount of fuses and extra weight of cable, to use a separate fuse for every single component. For example you are planning two completely independent circuits for your head unit. Depending on the way the unit is built one of the two feeds it needs will be using just a few milliamps and so it will be almost impossible to provide it with suitably low fusing. Given that the smallest cable you will sensibly be able to supply it from will be capable of supplying about 8 amps in open air there is no point in not putting other low risk items on the same circuit. You will not find any production car that has completely independent fusing for all equipment. Also if you are staying with Mini switchgear it's not even possible to get this level of separation. The headlamp flasher for example shares its supply with the horn inside the switch, and it is a different supply from the rest of the lighting switches. The washer pump shares its supply with the wiper motor too, again this is built into the switch.

Relaying the main circuit groups is a good idea, and features in some of my own designs, but as said you cannot use a regular relay for it. Also most high power relays are not up to the task of supplying their advertised output continuously for a long period. Technically anything supplying main power to equipment at high current and replacing the functions of a switch is called a contactor and they are built differently from relays. You will find that contactors for mains power that fit into fuse boards can carry very high currents for long periods. To do the equivalent in an automotive relay you will need to find a relay rated up around 100 amps. Essentially don't plan to use more than half it's advertised rating if you want it to last and remain reliable. It is also a very good idea to put the large, main cable you fit to the solenoid into a big mega-fuse box in the engine bay, giving the supply to each relay a large current fuse protecting all the wiring. This is also an effective way of splitting the cables up. Oh and forget the idea of using four way fuse boxes! There are lots of different boxes available out there and blade fuses are better than cartridges. The main auto electrical suppliers all carry a modular fuse and relay system that makes it very easy. It has bussing strips to join fuses together which saves a lot of hassle when it comes to actually building it.

I think you need to read up a lot more about the way the circuits in a car work first too. You have listed one fuse marked 'headlamps', at a very minimum you would need two and as said to make it safe you need four. Headlamps have two circuits, this is a very basic thing to understand in the wiring of a car. I would suggest you get yourself the Haynes Automotive Electrical Systems Techbook. It is very helpful in understanding the needs of not only the wiring and fusing but also the starting and charging systems. It lists all the wiring colour codes you need to use (they are British Standard and you should stick to them) and describes how many of the circuits actually work. Remember there are also various laws covering the way things are wired in terms of what is safe and usable in a car. The exact laws depend on the age of the vehicle but most versions of what are called the Road Vehicles Lighting Regulations and the Road Vehicles (Construction and Use) Regulations are available on line.

[tiger99]

I would add to what has already been said, correctly, that as well as being dangerous, a single headlight fuse is illegal. Realistically, you need 4 fuses, one each for main and dip in each side, downstream of the dip switch. The other way is to use two fuses, left and right, upstream of the main light switch, if you can find a double pole light switch and a double pole dip switch that will fit, which is unlikely.

If you use relays to take the load off the swiches, use one for each filament, i.e. four in total, as per the fuses, and give them seperate earths. But, if you add spots, which need to be controlled by a switch downstream of the dip switch so they only come on with main beam, use a single relay for both, fed from the battery/solenoid terminal (brown wires) via its own single fuse. Spots failing is not as serious, as the main beams will also be on.

Again, earthing has already been mentioned. Earth each light unit seperately to the shell, i.e. one earth point at each corner of the car. The standard arrangement of one earth from both headlights, via a bullet connector behind the grille, which corrodes, back to a single point on the bulkhead is unsafe, and does cause complete headlight failure. And, as has been suggested, fault finding is easier as there is far less risk of peculiar problems if an earth comes adrift.

[A362 TTU]

Firstly, thanks to everyone for the great info! - I know I will have, and will do make mistakes - Luckily, Its just a diagram - and mistakes wont cause a fire at this stage.

Obviously there are a few components missing, however the idea of a "kill" switch to prevent the engine from starting can be acheived by inputting it into the ignition circuit, thus the engine will turn over but will not start.

Once you have the circuit diagram, you will need to produce a "power" diagram, ie power consumption for each item, this will allow you to apply circuit balancing and correct fusing strategies, also think caredfully about your fuse box MTA do some pretty good units but they are not cheap, I am using an Early S type Jaguar fuse box in my Mini, the unit is made by a company called Yazaki, don't go for the newer rounded version as it is a pain.

Best bet is to get one form a breakers and use PIDG crimps with glue lined heat shrink to seal.

But whatever you do do not solder as this very bad, as solder will wick up the wire circuits causing fatigue failures and make sure that you use the correct tools,I have seen loads of good intentions ruined by poor tooling.

What software are you using for this project ? is that Visio ?

thanks for advising on the best position for the kill switch, I know that I will have to produce a diagram for "power" in the future. I will look up those physical parts when it is necessary. I knew not to solder before I posted this.

I used some free online software for the diagram - www.circuitlab.com

I think something mentioned before as been fuses on headlights, you use 1 fuse if it blows your in complete darkness...its best if fused to have separate for each side, which means 4 fuses when you include main beam and dipped

I will use 4 fuses for the headlamps (separate dim/dip for each) and probably 2 fuses for the spot lamps (1 per pair). thanks for that.

Yes each lamp unit would be requiring a seperate fuse and also a seperate ground point, not just seperate ground wire, but multiple grounding points to stop Back EMF, voltage going "up" the "down" route.

Alongside the power chart you will also need a grounding strategy.

and if you are using a relay for individual areas you will very rapidly run out of "current" room i.e. most relais will not function very long if you pull more than 30 may be 40 Amperes max

The method used is to remove the relais and fit buss bars, most modern fuse boxes will have buss bars that are either a solid bar with terminals stamped as a single part or a "multicrimp with 3 wires (max) one side and a feed wire the other side or a crimp specially made with a number of terminals one side and a circuit feed the other.

So what circuits need separate grounds? I was probably going to ground each circuit very close to its end.

I see now that the use of relays in the diagram are inappropriate - as current draw would be constant through those while the car is being driven, so I will look up busbars as an alternative - I will most likely end up buying a modern fuse box that includes them if i implement this build.

No worries, I guess the big danger is over complicating..Can't really say there was much wrong with my 1984 loom all worked, just I shorted a main power feed a few years ago and it melted the loom..only reason I rewired mine really..

Did you rewire yours back to standard?

I added an ECU, with launch and traction control and 2 sets of spots, no radio though as the SCCR box is enough music to my ears. I then rewired the whole lot in about 1999, 2000 I applied the hierarchial logic to the wiring harness and never had any issues, if one lamp went out I still had plenty of other lighting

I may design this to wire in a megajolt, and move away from my plain electronic ignition at the same time. I presume by hierarchial logic you mean having multiple failsafes for lights etc?

There is no point, and it will use a huge amount of fuses and extra weight of cable, to use a separate fuse for every single component. For example you are planning two completely independent circuits for your head unit. Depending on the way the unit is built one of the two feeds it needs will be using just a few milliamps and so it will be almost impossible to provide it with suitably low fusing. Given that the smallest cable you will sensibly be able to supply it from will be capable of supplying about 8 amps in open air there is no point in not putting other low risk items on the same circuit. You will not find any production car that has completely independent fusing for all equipment. Also if you are staying with Mini switchgear it's not even possible to get this level of separation. The headlamp flasher for example shares its supply with the horn inside the switch, and it is a different supply from the rest of the lighting switches. The washer pump shares its supply with the wiper motor too, again this is built into the switch.

Relaying the main circuit groups is a good idea, and features in some of my own designs, but as said you cannot use a regular relay for it. Also most high power relays are not up to the task of supplying their advertised output continuously for a long period. Technically anything supplying main power to equipment at high current and replacing the functions of a switch is called a contactor and they are built differently from relays. You will find that contactors for mains power that fit into fuse boards can carry very high currents for long periods. To do the equivalent in an automotive relay you will need to find a relay rated up around 100 amps. Essentially don't plan to use more than half it's advertised rating if you want it to last and remain reliable. It is also a very good idea to put the large, main cable you fit to the solenoid into a big mega-fuse box in the engine bay, giving the supply to each relay a large current fuse protecting all the wiring. This is also an effective way of splitting the cables up. Oh and forget the idea of using four way fuse boxes! There are lots of different boxes available out there and blade fuses are better than cartridges. The main auto electrical suppliers all carry a modular fuse and relay system that makes it very easy. It has bussing strips to join fuses together which saves a lot of hassle when it comes to actually building it.

I think you need to read up a lot more about the way the circuits in a car work first too. You have listed one fuse marked 'headlamps', at a very minimum you would need two and as said to make it safe you need four. Headlamps have two circuits, this is a very basic thing to understand in the wiring of a car. I would suggest you get yourself the Haynes Automotive Electrical Systems Techbook. It is very helpful in understanding the needs of not only the wiring and fusing but also the starting and charging systems. It lists all the wiring colour codes you need to use (they are British Standard and you should stick to them) and describes how many of the circuits actually work. Remember there are also various laws covering the way things are wired in terms of what is safe and usable in a car. The exact laws depend on the age of the vehicle but most versions of what are called the Road Vehicles Lighting Regulations and the Road Vehicles (Construction and Use) Regulations are available on line.

Wow! lots of great info Dan, thanks.

Firstly, I will probably move away from standard switch gear in the process - although maybe not the stalks, so I will have to factor in what you have said for them.

I take it you are recommending a book like this - http://www.amazon.co...c_df_1845842154 .

Once again, thanks for all the info everybody!!!!!.

[A362 TTU]

I would add to what has already been said, correctly, that as well as being dangerous, a single headlight fuse is illegal. Realistically, you need 4 fuses, one each for main and dip in each side, downstream of the dip switch. The other way is to use two fuses, left and right, upstream of the main light switch, if you can find a double pole light switch and a double pole dip switch that will fit, which is unlikely.

If you use relays to take the load off the swiches, use one for each filament, i.e. four in total, as per the fuses, and give them seperate earths. But, if you add spots, which need to be controlled by a switch downstream of the dip switch so they only come on with main beam, use a single relay for both, fed from the battery/solenoid terminal (brown wires) via its own single fuse. Spots failing is not as serious, as the main beams will also be on.

Again, earthing has already been mentioned. Earth each light unit seperately to the shell, i.e. one earth point at each corner of the car. The standard arrangement of one earth from both headlights, via a bullet connector behind the grille, which corrodes, back to a single point on the bulkhead is unsafe, and does cause complete headlight failure. And, as has been suggested, fault finding is easier as there is far less risk of peculiar problems if an earth comes adrift.

Thanks for all this info!. Only just noticed your post seen as I must have posted my reply seconds after you did (both at 12:14).

For earthing I am thinking of having the following setup -
4 in the engine bay (front left, front right, rear left, rear right).
2 in the 'cabin' (left behind dash, right behind dash)
3 in the boot (rear left, rear right, centre (battery + amp)

Should I be utilising more earth points than this?

Thanks again!.

[lrostoke]

Left my loom pretty standard apart from the lights I've run 2 separate feeds for left and right, so 2 x earths, 2 x dim, 2 x main 2 x sides...wanted get away from the spaghetti at the front which is normally the place to go hunting for bad connections.
Also because I converted from ballast I stripped out the ballast wire and run a new coil positive feed.

All the front loom from fusebox/ bulkhead is new wire now

rear loom is original.

[MRA]

Ground points, you would not want to ground lighting on the same ground stud, if one fails they both fail, then you are again blind, and as about 80% of auto electrical faults are ground related, you can easily see the problem :-(

also if you have an ECU coil pack or HID lighting which can easily spike at 1000v to ground and you couple up your lamps to the same ground and the ground point becomes insulated, i.e. fails. then 1000v will spike Back EMF through the lamps and kerpow (batman speak) no lights.

[Ethel]

Some of the online vehicle electrics suppliers have example circuit diagrams on their sites, and you could crib out of a Haynes (later Mini or Metro would be a good choice. There are also MJ wiring diagrams to find online.

The MJ is a good example for separating earths, (mostly because it'll help to keep the sensor signals clean) some even use blocking diodes to stop reverse currents, but that may be overkill. As you draw your diagram, include the earths as you intend to wire them and you'll be able to trace any potential reverse currents if an earth point isn't connected to earth - e.g. if you have a 20A headlight circuit sharing with a 5A sidelight you might want to follow the 5A circuit back and ask yourself how it'd function as a 20A ground.