loom building

[motorsportbeng]

I'm building a track car that's as much about the on track fun as it is the building and maintaining of it. I have been an engine builder for the last 4 or so years and the mechanicals of the car I'm fairly confident with but electronics have always been my down fall. I want to build a simple car loom with only the bare essentials like ignition, fuel pump, lights and wipers and that's about it.
I believe I find the current ratings of the components I want to use and use that to spec. what wire thickness and fuses I need. For everything apart from the starter switch I should be able to go battery > fuse box > switch > component > ground right? any help and advice would be great!

[stevieturbo]

Dependng on how much you need to include, might be as handy to buy some sort of kit ( ie fuse box and wiring )

Car Builder Solutions sells a lot of stuff, and Vehicle Wiring Products sells mostly components

But it all really depends exactly what the build entails. Draw it all out and plan everything then you can decide what you need to buy. Most stuff will be relatively low current, so can be easier to choose one wire size that does all. Saves buying huge varieties of wire sizes, which can be more expensive if buying full rolls.

Proper crimp tools, sleeving/heat shrink, braiding etc are all important. But that's all planning again

[blitzracing]

I like the 7 core trailer wire to make basic looms. You can run 7 cores to the rear of the car from the dashboard / fusebox , and 7 to the front which is enough for a simple loom.

[GnuBee]

motorsportbeng said:

I'm building a track car that's as much about the on track fun as it is the building and maintaining of it. I have been an engine builder for the last 4 or so years and the mechanicals of the car I'm fairly confident with but electronics have always been my down fall. I want to build a simple car loom with only the bare essentials like ignition, fuel pump, lights and wipers and that's about it.
I believe I find the current ratings of the components I want to use and use that to spec. what wire thickness and fuses I need. For everything apart from the starter switch I should be able to go battery > fuse box > switch > component > ground right? any help and advice would be great!

You don't normally directly switch loads such as fuel pump, rad fans, lights instead they're normally switched via a relay. You can directly switch the loads but this will neccessitate running the appropriately rated wiring throughout and using appropriately rated switches.

It's not clear if your intending to create a road legal car but if you are the loom complexity will increase because you will need to support indicators, hazard lighting, 2 speed wipers, horn, number plate lighting etc.

For supplies use Pole Volt or Vehicle Wiring Products; you'll be able to obtain all the cable, connectors and ancillary items from these 2 companies.

[crogthomas]

If you want to make it really easy for yourself, lookup 'Painless' wiring looms. They're mainly used for building hot rods, but there's no reason why you couldn't use one on anything else. A complete wiring loom with all the fuses and relays you need. All you need do is cut the wires to length and secure them in place.

I've had the pleasure of making some additions to a car that has used a painless loom. The whole thing was very well thought out and came with a clear wiring diagram that was very easy to understand. Painless you might say. It's a US made product, but I assume you can get them over here from one of the many hot rod specialists.

[Nick1point9]

I take you have a seperate wiring harness for the control system firstly!

with regard to simply powering lights/starter/fuel pump etc you should do this with relays. Where possible, you should reduce the current draw at the switch you physically use as much as possible.

But above all else the most important thing is to use the right tool for the job. Wiring can be fiddly but if you properly assemble connectors/switches/relays etc then you will make a much more reliable harness.

Finally, don't forget to strain relieve all wires - google "service loops" for info on this. this also makes repairs much easier.

[motorsportbeng]

Thanks for the replies. It is a track only car so no road regulations to meet. I have a MBE ecu and engine loom from a Caterham as it is the same engine in my Fiesta that I was hoping to tidy up and replicate it. I want a switch to power the ecu, a switch to run the fuel pump, a starter switch, a switch to run rear lights as a rain light and a switch to run the wipers and probably rear indicators as well for signalling in on track days. Can anyone enlighten me on how to spec what relays to run or point me in the direction of some information that can?

[stevieturbo]

motorsportbeng said:

Thanks for the replies. It is a track only car so no road regulations to meet. I have a MBE ecu and engine loom from a Caterham as it is the same engine in my Fiesta that I was hoping to tidy up and replicate it. I want a switch to power the ecu, a switch to run the fuel pump, a starter switch, a switch to run rear lights as a rain light and a switch to run the wipers and probably rear indicators as well for signalling in on track days. Can anyone enlighten me on how to spec what relays to run or point me in the direction of some information that can?

As at least two people have already mentioned

http://www.vehicle-wiring-products.eu/VWP-onlinest...

You should not need a switch for the fuel pump, the ecu should control it

How your ecu is installed and wired will dictate how many relays etc are required for that aspect. It may require one or more depending on how injectors, coils and other items are configured.

Any standard automotive relay will be fine for any basic functions

And as mentioned already, Painless in the US do offer pretty good complete kits. But as they're from the US< they can end up pricey by the time they are here. But they are good and have plenty of wire on them. But they would no doubt still need modified to some degree

http://www.painlesswiring.com/webcatalog/Keywordse...

Other alternatives for complete kits. No idea if anyone in the UK offers similar. Although these look like good value

http://stores.ez2wire.com/StoreFront.bok

http://www.autowiringsolutions.com/item.php?item_i...

A slightly more sophisticated system

http://spaghettimenders.com/RCS.html

[motorsportbeng]

Thanks for the responses, I know the complete kits would be easier but I want to do it myself as a learning tool. I will hopefully be receiving a wiring diagram for my ecu next week, I was under the impression it didn't need it's own relays but may well be wrong. Studying for a motorsport degree I'm trying to practice running the numbers at the moment so I've got a basis if I have to do it for a job in the future. What do you do to work out if a relay is required and what rated one if so?

[stevieturbo]

motorsportbeng said:

Thanks for the responses, I know the complete kits would be easier but I want to do it myself as a learning tool. I will hopefully be receiving a wiring diagram for my ecu next week, I was under the impression it didn't need it's own relays but may well be wrong. Studying for a motorsport degree I'm trying to practice running the numbers at the moment so I've got a basis if I have to do it for a job in the future. What do you do to work out if a relay is required and what rated one if so?

What exactly is the motorsport degree in ? Working out if a relay is required and/or current is basic high school stuff.

A relay is just a remote switch. It allows a low current switch/trigger to turn a high current load off/on.

http://electronics.howstuffworks.com/relay.htm

[Incorrigible]

It will depend on what Caterham engine loom you have and what engine

With a standard ECU there is a Multi function relay unit (MFRU) that controls the fuel pump, starter motor, and engine power (for the injectors spark, IACV etc)

You can bypass this but you would need a separate relay for all the individual functions

Also you will need to prime the fuel system (the MFRU has a timer on it to do this) and also a safety cut out to remove power to the fuel pump in the even of the engine stopping. Imagine a worst case scenario: the engine stops because of a fractured fuel line, and the pump carries on pumping fuel.....

What engine is it ??

[stevieturbo]

Incorrigible said:

Also you will need to prime the fuel system (the MFRU has a timer on it to do this)

The ecu virtually always controls this. Certainly on any car Ive ever come across unless you're going back 20-30years

or is it some weird Caterham thing to do otherwise ?

Edited by stevieturbo on Sunday 25th March 14:21

[Nick1point9]

motorsportbeng said:

Thanks for the responses, I know the complete kits would be easier but I want to do it myself as a learning tool. I will hopefully be receiving a wiring diagram for my ecu next week, I was under the impression it didn't need it's own relays but may well be wrong. Studying for a motorsport degree I'm trying to practice running the numbers at the moment so I've got a basis if I have to do it for a job in the future. What do you do to work out if a relay is required and what rated one if so?

Put very simply, any electronic device that is on/off should be driven by a relay. When specifying a relay/fuse/wiring you need to look at what the peak current flow will be: remember that motors will "spike" when initially switched on. This is a pretty fundamental part of an electronic device so it should be readily available information.


Add a safety factor of +25% for the fuse, and then about +100% for the wiring, and the relay: the last thing you want is for the wiring to melt because it is close to its limit. The fuse should always be the weakest link.

[motorsportbeng]

It is a motorsport engineering degree but we have only just started vehicle electronics. I am aware of what a relay does but I am unsure as to what level is the cross over between needing a relay and not. I need to look into the engine loom side of things a bit more but every track car I've driven the fuel pumps are ran from a switch on the dash and should the worst happen the pumps are cut when the master switch is turned off. It is a ford sigma/zetec se engine. When I first started with the engines I came across several websites and videos etc. with information but I can't find much when it comes to car looms, are there any decent ones I should be having a browse at?

[stevieturbo]

motorsportbeng said:

It is a motorsport engineering degree but we have only just started vehicle electronics. I am aware of what a relay does but I am unsure as to what level is the cross over between needing a relay and not. I need to look into the engine loom side of things a bit more but every track car I've driven the fuel pumps are ran from a switch on the dash and should the worst happen the pumps are cut when the master switch is turned off. It is a ford sigma/zetec se engine. When I first started with the engines I came across several websites and videos etc. with information but I can't find much when it comes to car looms, are there any decent ones I should be having a browse at?

Whoever is wiring those cars should reconsider. If I was trapped in a burning vehicle with fuel pumps still running and incapable of operating the battery kill....it would be a nasty situation.

It is basic safety that the ecu controls the pump, and if the crankshaft is not rotating, the fuel pump doesnt run.

As for needing relays. Strictly speaking you dont. As long as any switches used can handle the full current of the load they are switching, no relay is needed.

But this can mean more awkward, bulky and expensive wiring and of course more expensive switches.

It's really just more convenient and neater to use relays for most things.

[motorsportbeng]

I see what your saying actually, but the cars definitely had separate fuel pump switches to ignition, perhaps these switches were linked to the ECU. I will have a read of what ratings my electrical components are and what outputs and inputs the ECU has and go from there

[sedicirich]

I have done all the things you want to do, and as the other have said you dont switch items using switches you do it via relays. The main wiring in my car is roughly this

Battery > kill switch > main power feed to Ignition relay/fuel relay/fan trip(50A)/starter motor

>Ignition relay goes to the fuse boards (this relay is controlled by the ignition switch (just of the picture below in red) which in turn is grounded via the ECU igintion wire (as per OMEX wiring instructions)The ECU gets it power direct from the kill switch with a 1amp fuse.

>Fuel relay is controlled via the Green switch and grounded via the ECU fuel pump wire

The ECU gives you 3 seconds to start the car once, the ECU does not read a crank signal it turns off the ignition and fuel relay (makes sense to me)

>The engine loom is largely seperate from the rest of the power loom with power provided for the injectors, the coil. All other engine bits go straight to the OMEX main plug - note the ECU only grounds items for example it does not power the injectors it only grounds them to get them to open hence the ECU needs good earth but only a small power supply.

>Rad fan trip goes to rad fan relay which is controlled by the ECU

This is the main config, theres a few other bits to it (alternator goes to switched side of kill) but it will get you started. Remember the golden rules - Relays do the power switching not switches, The ECU only grounds things and does not power them.

Fuse board 1 and switches for relays

Fuse board 2 is under the DL1

[motorsportbeng]

thank you for the responses that was very insightful!

[The Black Flash]

stevieturbo said:

Whoever is wiring those cars should reconsider. If I was trapped in a burning vehicle with fuel pumps still running and incapable of operating the battery kill....it would be a nasty situation.

It is basic safety that the ecu controls the pump, and if the crankshaft is not rotating, the fuel pump doesnt run.

As for needing relays. Strictly speaking you dont. As long as any switches used can handle the full current of the load they are switching, no relay is needed.

But this can mean more awkward, bulky and expensive wiring and of course more expensive switches.

It's really just more convenient and neater to use relays for most things.

Probably in series I'd imagine? In my kit I've a fuel pump switch on the dash, but it's in series with the ECU *and* an inertia switch. So if any one of them is turned off, the pump is killed.