New Mi16 Harness Build

[sport1901966 8]

I've just got round to writing up my build of a new Mi16 loom for the 205 conversion and thought I'd post it up here as hopefully it'll be of interest to you guys. Be warned - it's a bit of a longun!

 

When I bought the Mi16 engine ready for the conversion it came with the BX16v harness that had been partially modified already. Unfortunately, it was a bit of a mess but after a bit of time spent with a multimeter I had got my head around it. I made some repairs and judged it was ok to use, at least temporarily.



Having fitted the harness I then discovered the ECU would not run the fuel pump as it should. The software logic in the ECU is designed so that the fuel pump will run for about 1 second as soon as the key is turned to the ignition position, then, when the key is turned to the starter position and the engine turns over, the ECU will detect a signal from the Crank Angle Sensor (CAS) and activate the fuel pump to start supplying fuel (it continues to do this all the time it is receiving a signal from the CAS, i.e. when the engine is turning) . From a wiring point of view the ECU controls the fuel pump activation by earthing the Fuel Pump Relay. However in its current state the original harness didn’t do this, and even having spent ages checking it over I couldn’t work out why, I even got to the point where I suspected the ECU of being at fault. To get by I wired the Fuel Pump into a toggle switch on the dash.

The other obvious flaw to this harness was the length due to the ECU being mounted under the driver seat in the BX16v. Because of the condition of the harness and the poor layout in the 205, I had always intended to build a new harness specifically designed for the conversion in both layout and fundamental wiring design.

This time came around sooner than planned as I had a few teething problems during the early days of running the car. First was the melting of a whole chunk of the harness when the bonnet scissor prop cut into the loom and earthed the main live cable:



The repair ended up like this:



Following this the fan blades on the alternator cut through the Crank Angle Sensor shielded cable, obviously completely stopping the engine from running. Which prompted the fabrication of this:



Obviously the original condition and the subsequent repairs to these issues left the harness open to all kinds of reliability issues so I got started with designing the new harness.

[sport1901966 8]

Initial Considerations

It’s not something I have done before so I wanted to come up with a robust process, and maybe some tools, that I could re-use when designing a harness for a future aftermarket ECU project. The major things I needed to know were:

1. Harness layout (lengths, branch points, etc)
2. Wiring connections
3. Cable Cross Sectional Area (CSA)
4. Connectors and Terminals required (type/cable size etc)
5. Other Cable Accessories – Heatshrink, Convoluted Tubing, Fusing etc

Before starting the design of the harness I had in mind a couple of minor tweaks I wanted to make to the original wiring.

From a general perspective I planned to use colour coded cable depending on functions, and to be as optimised as possible with the wire thickness selection.

Layout
In terms of the layout I decided I would mount the relays to the O/S suspension turret, and due to the loss of space around the slam panel due to the air filter, the power distribution block would be mounted on the N/S suspension turret.

Ignition 12v Input/Tacho Signal Output/Fuel Pump 12v Output
Instead of introducing the Ignition 12v and Tacho Signal connections within the engine bay as shown below, I decided to make the connections under the dash directly to the correct wires on the 2 brown plugs. I also combined the Fuel Pump into the same connector making it a 3-way connector.

The reason for doing this was to take the Sensor Loom out of the equation for reliability (not renewing this yet) and to make the Engine Harness a little more standalone.

 

Current Ign 12v input and Tacho Signal output

 

Underdash brown plugs

Diagnostic Connections
I wanted to incorporate the MIL lamp output and diagnostic switch into a single connector located in the cockpit area of the harness, to eventually mount a lamp and switch in the dash so diagnostic checks would be easier.

Inclusion of Inline Fuses
After the harness melting incident I decided I wanted fuses at the points of power entry into the loom. This included the main permanent live feed and the ignition live feed.

[sport1901966 8]

Design Process

After some careful thought I came up with the process below as it should be transferable to any application, requires minimal trial and error, ensures a working harness first go (hopefully) and enablee efficient ordering of cable etc with minimal waste.

1) Harness Layout

I decided the first step would be to set the harness layout, knowing basically what components are required and their location (with my previously mentioned adjustments in mind).

I did this by going out to the car armed with some string, masking tape, a pen, paper and a tape measure. I started at the ECU plug and used the string to trace the intended path of the harness and the branches, then measured the lengths and recorded them on a sketch of my intended layout that I created as I went through the process. Where connectors will be on the end of sections of cable, I took the length as being to the furthest point within the connector – e.g. the ECU connector I measured to the furthest terminal.

When I had the basic harness layout diagram with all the lengths and branches I then started labelling on what connectors would be required with the following info [connector type/gender/connector size (available no of terminals)/actual no of terminals used]. Using some software called SmartDraw I ended up with a diagram along the lines of the one below:



2) Wiring Connections

The next step was to create the wiring schematic based on the harness layout from the previous step. Most of the connections were self explanatory but those that weren’t I worked out either through research, or testing of the standard harness/components. At this point the fusing I wanted to introduce was also planned in. This resulted in the diagram below:



I then decided on a colour system (then re-did it based on what colours are actually available!) and applied it to the diagram:



3) Cable Cross Sectional Area (CSA)

For this stage I made a tool in excel that would help me to calculate exactly what cable I needed by Colour, Diameter and Length. It was a little time consuming, but actually saved a load of time when it came to actually building the harness, as all the individual wire lengths that needed to be cut were in a convenient list. Below is the cable entry table:



To use the tool the first step is to specify a contingency length – this is added to each cable length (a percentage value may be better but for the time being I decided this would be adequate). After this, using the layout diagram and colour coded wiring diagram, every variation of cable length is listed in the first column of the table. An important consideration is where butt connections will be made – I used some translucent adhesive heatshrink butt connectors, with these I had to subtract 3cm from the pre-branch cable, and add 3cm to the post-branch cable. This ensured that the butt connection was complete before the split, and hence the split is in the correct position. In the next column the number of cabled that are of each length are entered. The colours and a description of each of these individual cables are then filled out in the relevant columns. The lengths of each of the individual cables then need to be entered in the next column (same as the length filled in the first column, but it has to be repeatedly entered for every cable in that group in this column). Finally the required CSA for each cable needs to be entered into the last column – see section below for methods to select the CSA.

Deciding Cable Cross Sectional Area (CSA)

a) Recommended/Rule of Thumb by Application

A number of cable suppliers will give suggestions for the applications of the cable sizes they use. Also there are a number of other sources that will give recommendations, such as aftermarket ECU suppliers. I started with this method but couldn’t find information I was happy to completely depend on. I did however start putting it in a table



Look up component specifications

Every component will have specifications that will determine the cable CSA required – wattage ratings, or current ratings etc. This would be the ideal method, but finding this information is quite difficult.

c) Measuring Old Harness Cable Diameters

This was my preferred method for a number of the wires for my harness as it was fairly quick and pretty conclusive.



d) Measuring Current with Existing Harness Fitted

For some wires I couldn’t find any information online, or any similar application to measure. In this case I decided to take current measurements from the existing harness in situ. I made some measurement harnesses, then fitted them between various sensors etc enabling measurement of the current (as current has to be measured inline). Below is a photo showing the measurement of the AFM currents.



Note: Now the cable current capacities are specified the fusing values can be selected – you fuse to protect the wire, whereby the fuse will fail before the current capacity of the cable is exceeded

Once the table is filled out the spreadsheet calculates the lengths (inc contingency) required of each colour and CSA combination and presents it in a table like so:



4) Connectors and Terminals

The next stage is to tabulate the connectors required from the harness layout diagram, then using the wiring diagram and cable size list, note down the terminals required to go in each connector. Obviously where the harness is interacting with external components i.e. sensors/ISCV etc the connector type will have to match that of the components, for connections within the loom it is personal preference, but sealed, locking connectors are recommended, such as Junior Power Timers.



5) Other Cable Accessories

This is the last stage of the design process, using the layout diagram the lengths and sizes of required convoluted tubing, heatshrink should be selected. Any fuse holders required and any consumable items should be planned.

The design process is now complete, and you should have a list of exactly what is required to build the harness.

[sport1901966 8]

Build Process

1) Cabling

When I received all the cable I printed out the table created in the excel tool. This then gave a list of every individual wires Colour, Size and Length, which I then used to cut the wires to size. As I went along I laid the sections out on the floor as per the layout diagram. As it build up I used sandwich bag ties to keep the cable together – Velcro cable tidies would be even better for this but I didn’t have any.

The kit ready to go!

 

Laying it out at various stages





I used tape and/or small cable ties to mark the branch locations



Heatshrink Butt Connectors (I found these really good)



As I went along cutting and assembling the cable I used a dymo label writer and clear heatshrink to label each wire for its function. This is mainly for even easier connector assembly, diagnostics in future.



2) Connectors

The connectors are fairly self explanatory, however be sure to feed on any seals/ covers/ heatshrink/ sleeving before crimping on the terminals. I used connector corrosion protector grease on each terminal as I crimped them on.





When it came to the inline fuse holders the type I bought were connected to the cable using spade terminals so I decided to use adhesive lined heat shrink and fabric tape over the connections to bind the connections together.



3) Cable Accessories

For things like the convoluted tubing it was simply a case of cut to length and fit to the loom, I used fabric tape to link the ends of the tubing. To seal the open ends of against the connectors I used self amalgamating tape. The basic idea with the cable accessories was to protect the harness from abrasion, vibration and water as best as possible.

[sport1901966 8]

The Finished Harness

After quite a few hours, very sore fingers and a few burns from heatshrink I was left with this:



Fitting to the Car

Before fitting it into the car I wanted to check it worked without removing the original harness. As the final fit would require some modification to the vehicle harness and injector sub-harness (which I later decided to fully rebuild anyway) to suit the connectors I used on the Engine harness, I needed to make a couple of small temporary link looms. One was to bring the Ign 12v input, Tacho output and Fuel Pump output next to the under dash brown plugs. The other was to adapt the current injector sub-harness connector to the new one I would eventually be using.

Injector Sub-Harness Connector Adaptor



Under Dash Adaptor

A couple of general pictures of the trial fit









To my absolute amazement (I had been building the loom on and off for about a year so could easily have missed something) it started first time AND even better, the ECU was running the fuel pump as it should be!

All that was left to do was fit it fully. To do this I needed to create the new power loom with the extended section enabling the power distribution block to relocate on the N/S suspension turret. To make the power harness I used the same process as the main harness and it worked without a hitch. Also as I mentioned earlier I built a new injector sub harness to improve reliability and ensure that the injectors are still getting the signal they should.

I had it fully fitted around May 2012 and in the summer the harness got a proper test. I found myself stuck on the M25 for about 2 hours in nearly 30 degree temperatures, the engine ran without a single hiccup so I consider it proven!

Edited February 26, 2013 by sport1901966

[pugpete1108 62 1 Cars]

good job, i did the entire engine managment for my ms setup. to every component in the engine bay.

 

twas a headach getting it the right length off of the car so still had to make some adaptions when fitted to the car itself.

 

and yeah i feel the pain with the sore fingers, you would think by now they would be like old leather, but no.

[m_attt 31 1 Cars]

looks very professional, Given me some ideas as need to do this on my turbo

[GLPoomobile 958]

Looks very good I spent days and days and days desiging and building my loom. Wish I'd had a Dymo labeller at the time, as it really adds a nice touch.

 

On your brown under dash plugs, check your Ignition live terminal is tight and secure. On mine, the original loom had a 2nd (unused) terminal jammed in to the slot with the live terminal. I couldn't understand why. I did figure out why after spending a very long time trying to work out why my engine would intermitantly stall and refuse to start. It was becuase my terminal was loose in the holder (hence why the previous loom had 2 terminals jammed in the one slot). It wasn't obviously loose either, the amount of free movement was tiny, but it was enough to break the connection in the plugs.

[Anthony 1,000]

Good job

 

This is something that most Mi16 looms are needing these days, as most that I see are in very poor condition, and that's usually before they've been exposed to the harsh environment that is a 205 engine bay. Most 205 Jetronic looms aren't a whole lot better either.

 

Where did you get the replacement pins for the Motronic connector btw, as I'm assuming they're not a standard JPT type pin?

 

The only changes I think I would personally have made would be to have made the injection sub-loom part of the main loom (like on 405 looms) to remove another potentially problematic connection, and to relocate the relays inside the car next to the ECU away from the elements, both in the name of reliability and packaging (as I've never liked them behind the drivers headlight), but they're both minor points.

 

Oh, and the main power feed should be fused in the shuntbox so you shouldn't need a separate in-line fuse for that connection, although clearly it's not going to do any harm.

[GLPoomobile 958]

Anthony, if you mean the terminals in the ECU plug, they are indeed standard JPT terminals.

[Anthony 1,000]

That is what I meant - makes things much easier if they're just standard JPT pins

[sport1901966 8]

Thanks for all the comments. Hope it can be of help to someone.

 

Thanks for the heads up on the ignition live, fortunately I've bypassed the brown plugs with the tacho sig, ign live and fuel pump feed so should be ok.

 

As GLP says the ECU plug uses Junior Timer/Junior Power Timer terminals, I did manage to find a new ECU plug on Polevolt.com with saved disabling the original loom before it was fully tested.

 

Good points about the layout, initial I hadn't planned to redo the injector harness, but I would have to agree with your thoughts.

 

That's what I would have thought, but as you say no harm being doubly sure.

[NFS 32]

Fancy doing a loom for a xu10 j2te? i have one in that works atm but the guy tha did the loom left loads of unused plug on and its a mess.

[petert 550]

Nice work, but have you seen this stuff?

 

http://www.ebay.com.au/itm/230661544820

 

It's cheap, available in many sizes, far more flexible and looks very professional. I've made three looms this year with this stuff. Love it. He'll bag multiple sizes into one bag and charge one lot of postage.

[sport1901966 8]

Nice work, but have you seen this stuff?

 

http://www.ebay.com.au/itm/230661544820

 

It's cheap, available in many sizes, far more flexible and looks very professional. I've made three looms this year with this stuff. Love it. He'll bag multiple sizes into one bag and charge one lot of postage.

 

That does look good - does it have good abrasion resistance?

 

Will keep that in mind when I finally get round to building the loom for my new ECU

[petert 550]

So far so good. Here's a portion, the injectors. I used 1/8" for individual and 3/8" for the mains.

[m_attt 31 1 Cars]

what label writer, and what size tape did you use? cheers

[sport1901966 8]

I used a Dymo Rhino Pro 1000 with 9mm tape. Its good as it has a few electrical symbols built in too.

[S@m 156]

I'm very impressed by this since i'm currently giving my bx loom a spruce up (nothing to this extent though) - out of interest what relay holder are you using for the injector/fuel pump relays?

[sport1901966 8]

Thanks very much!

 

The relay holders were from Polevolt, this is a link to the kit I bought - http://www.polevolt.co.uk/acatalog/info_RBS1UKIT.html