At the heart of many a Cossie catastrophe is a dodgy electrical system, which is why Ade Brannan is here to tell you, from first-hand experience, what goes wrong, why, and – most importantly – how to overcome the problems to enjoy a reliable, untroubled Cosworth YB!


Over the last five years I’ve seen everything from slight misfires to full-on engine fires; knackered turbos to full engine meltdown. I’ve learned my lesson the hard way. The mighty YB motor is in reality very sturdy and can put up with enormous amounts of abuse, but the constant recurring issues always seem to be based around underlying engine electrical issues.

To help you avoid the same situation, and to allow you to benefit from my (costly!) mistakes we’ve put together a full guide on Cossie electrics, so if you want to learn how to read the signs of impending doom, master how to avoid them, and understand how to the get the very best possible performance from your YB-powered fast Ford then read on…


image by Adrian Brannan - 07779 695 234 - -

A loose injector plug was the reason for all this damage!


The problems with my Saph’s electrics started way back before I even owned it. Not long after my mate Chris had bought it (two years before it was sold to me!) the Cossie suffered catastrophic failure. A melted piston was the result of a high speed run with an incorrectly-fuelling YB, and the damage was so messy it even took out the block and cylinder head too!

This resulted in a whole new engine having to be sourced and rebuilt. Not cheap! The autopsy revealed all this pain was caused by something incredibly simple to fix and utterly-avoidable – a loose injector plug! It might have looked OK at a glance but vibrations from the running engine caused it to bounce a fraction from the correct seating position, breaking electrical contact with that injector and allowing one cylinder to run lean enough for a full engine meltdown!

Many people think that as long as injector plugs are connected and the car is firing on all four cylinders at idle, that’s enough, but this simply isn’t the case. In fact, an intermittent fault like this is much more dangerous than disconnecting the injector altogether. In this situation, with intermittent electrical contact, the injector still spraying partial amounts of fuel, which causes the air/fuel mixture to lean out and ultimately total engine destruction!



Ill-fitting distributor caps can cause all manner of running issues

Standard ignition
The stock distributor-based ignition system may have worked when the Cossie was new but add almost 30 years of wear and tear, plus the extra demands of a tuned engine, and you’re just asking for misfires. The small plug gap settings required for a big power YB also hinder the performance potential too.

I was constantly plagued by ill-fitting aftermarket distributor caps, and then by ignition leads that managed to corrode from moisture in the most mysterious of ways with no visible signs until one simply fell apart during a plug change! I at least started saving money on plugs at this point when it became apparent that a dodgy lead was the real issue, not dead plugs!



Things got so hot that it even caused a small engine bay fire!

Hot running
In my early days of Cossie ownership the car continually ran hot. I was initially blasting around tracks thinking that this was just the way things were with a Cosworth. But even when I got a standalone temperature gauge and an AFR gauge to properly keep an eye on things, it still resulted in turbo failure from excess heat… and then the incredibly hot downpipe set fire to some bulkhead sound deadening!

Taking it to a local dyno didn’t help either, as a twiddle of the CO screw while caning it on the rollers only resulted in the voltage pack melting clean off the side of the alternator as it was so hot! Another garage’s fiddling with the fuel pressure only masked the underlying problem as the entire calibration was shifted out of sync, resulting in some horrendous fuelling settings. I also later learned that the fuel pressure regulator should be left fixed, and capped as it can leak vacuum!

The issue was later identified by MSD as an old crudely written map and, most importantly, a simple break in the loom to the coolant temperature sensor that was playing havoc with the fuelling! This was when I realised that specialist help was really the only way to go.


Stewart wasn't impressed with the engine's performance

Stewart wasn’t impressed with the engine’s performance

Anti climax
On my first trip to Cosworth experts Motorsport Developments things definitely improved, but there was only so much that could be done during the one day we had booked. The problem was a number of typical faults reared their head; the wiring as previously mentioned, then on the dyno it was discovered that even when set correctly the fuel pressure regulator wasn’t allowing the correct flow of fuel. With this replaced the car performed reasonably, but the injectors just couldn’t supply any more fuel to produce any more than 302bhp. That may not sound bad but a Stage 3 Cosworth with T34 turbo is generally expected to produce over 330bhp.

The reason the fuelling was maxed out at 302bhp was completely down to the wiring. Firstly that the battery voltage at high revs was much lower than the alternator voltage, and the fuel pump had a significant voltage drop too, also due to poor wiring. Voltage in this type of setup directly relates to the amount of fuel that is delivered from the injectors, and the dismal sub-11v readings at the redline were nowhere near the ideal mid 13v readings that are desired.

A second trip was scheduled after many mods were applied. With an alternator rewire, fuel pump rewire, plus larger grey injectors the result was a safe 340bhp, but the injectors were still running at almost maximum duty and performing well below par. This setup felt great on the road, but the nagging doubts in my mind about the poor power supply and old bodged loom’s potential for erratic failings were always on my mind…


Ade's Saph went to Auto Dynamix for a full electrical overhaul

Ade’s Saph went to Auto Dynamix for a full electrical overhaul


I’d known about James Wills’ work at MSD for some time and always knew that his looms looked great, but it wasn’t until experiencing first-hand the negative results of old wiring that really made me appreciate just how invaluable his looms really are. By the time I had decided to take the plunge James had moved back to his home town of Paignton and set up his new business, Auto Dynamix. He still supplies MSD with his products, but now spending much more time himself getting involved in fitting, diagnosis and custom wiring products. Plus on top of that also doing remaps and regular garage work with a clear Ford bias. It might have been the other end of the country (a trip from Glasgow to Devon isn’t really classed as local!), but it’s only a day away, and it meant the man himself could get a proper look over the whole car…


The old loom was in a terrible state

The old loom was in a terrible state

The old loom
I knew the loom in the Saph looked pretty rough, but I didn’t quite realise just how bad it was. As James set about detaching and unpicking it from the bay he was instantly filthy. Even though my new engine had only recently been fitted the loom was caked in oil from decades of vapour, spills and leaks! Most of the insulation was unravelling and almost every wire looked brittle and ready to crack!

The factory looms even contain joins which look almost of DIY quality. These joins are breeding grounds for problems – even if they don’t come apart they can still gather moisture and corrode until they cause electrical issues.

My 2WD loom may just have been suffering from age and abuse but later Cosworths suffer from even more prominent design flaws. The Escort Cosworth has a large multiplug for example which is notorious for corrosion related issues, and the RHD 4×4 Sapphire has an engine loom which has a pointless loop of wiring designed also for LHD applications which loops back on itself right over the turbo downpipe, the hottest part of the car! No surprises that this area of wiring doesn’t fare well after many years of harsh heat cycles!

Also, delving deeper, it was found that even the wiring to the ECU in the area above the glovebox was riddled with dodgy old patched in repairs. Mostly relating to previous immobilisers…


Upgrading to a solid state wasted spark ignition makes a lot of sense

Upgrading to a solid state wasted spark ignition makes a lot of sense

Ignition upgrades
As I arrived at Auto Dynamix my car was still running a distributor, but with a full new engine loom going in it seemed mad not to take advantage of the potential to upgrade to a solid-state wasted spark system. The kit uses a Ford coil pack and custom made leads, along with an extra ignition amplifier. To make the ECU understand all this extra tech a driver board must be fitted into the ECU. Any of the Weber Marelli ECUs can accept the modification, and I was tempted to try it myself as I had already DIY fitted the closed loop driver board (which is great for off boost economy) but after seeing some examples of badly adapted conversions I’m glad I didn’t! The wasted spark installation is considerably more involved requiring some very intricate soldering and nerve wracking cutting of existing connections within the ECU.

As a result of fitting wasted spark you’re left with an ignition system with a much stronger spark, so compromised tiny plug gaps are no longer required, resulting in smoother running, better mpg, and more complete combustion, and of course there are no moving parts so there’s nothing to wear out!


New loom not only looks pretty, but with no cuts, joints, or crimps it supplies a constant voltage to all components

New loom not only looks pretty, but with no cuts, joints, or crimps it supplies a constant voltage to all components

The loom
James had already completed my custom spec loom before I arrived, complete with integrated wasted spark sections. The option for an integrated fan loom and anti-lag and launch control looms are also available for a small fee, but I had already previously fitted these separately.

Each loom starts with a core of three high quality heavy duty extra thick Raychem shielded wires for crank, phase and knock to eliminate any signal noise. High quality cable is used for all other components, but James prefers to keep clear of the trendy ultra-thin and lightweight Raychem stuff usually as he’s found that it isn’t as practical as conventional wiring in everyday applications. Plus the weight savings are so marginal that only top level motorsport would really see the benefits.

The ECU is grounded from the factory points to avoid any noise being introduced. Something not all aftermarket looms cater for.

A significant upgrade to the original design is the inclusion of a triple relay system to supply power to separate areas. The original Ford design is heavily stressed so this separate system allows the flow of current to reach vital components unhindered without being unnecessarily diluted by components of lesser priority. Areas such as the injectors and ECU especially require maximum current, so every bit helps.

An Auto Dynamix loom proudly has no cuts, joins or crimps internally, as these can often fail. James even explained how the middle of his looms could be submerged in water and still function perfectly! In addition to the top quality nature and engine saving abilities of these looms they are completely customisable. James has previously built fully tucked looms which can barely be seen, 8 injector looms, concours OE look taped looms instead of the usual braid and also several for engines which aren’t in their originally intended car. Another more typical and practical option is that of multiple hidden immobiliser options. Much more effective than the way typical alarm fitters will cut into an existing loom! The main thing is that the fresh new loom will give consistent voltage, and typically give results on a mere 0.2v drop between idle and 7800rpm! Not bad considering many Cosworths (mine included) are trying to make do with a huge 3v drop! A recipe for disaster!


Fuel pump rewire kits are available off-the-shelf and are well worthwhile

Fuel pump rewire kits are available off-the-shelf and are well worthwhile

Fuel pump
A pump rewire is essential on a Cosworth considering the age of the wiring, the stress that the OE relay is under and the current an uprated pump will draw. After my first MSD visit I had the Cossie’s 044 pump rewired, but not all pump rewires are equal! It tuned out that mine was made up of household wiring and a second hand VAG fuse holder with the most miniscule wiring and a relay robbed out of an old BMW! To make matters worse the way the earth was wired at the fuel pump end rendered the whole exercise pointless. It was probably worse than what was there to start with!

After discovering this horror, and being a mixture of amused and bewildered at just how bad it was James got to work on fitting one of his off-the-shelf pump rewire kits. Already made perfectly to size with terminals ready to bolt on, it’s a quick and easy job with just a bit of interior trim removal needed and feeding the wiring through the boot floor grommet. Instant voltage improvements were then recorded at the pump even at idle, so at high revs the difference will be significant.



Adding a second power cable from the alternator to the battery is an easy way to help improve the engine’s voltage supply

Alternator wiring
One of the most significant upgrades that can be made to the Cossie’s overall voltage is a surprisingly simple one. The culprit is the thick power cable which supplies power from the alternator to the battery. Over years this vulnerable cable is perilously close to the incredibly hot turbo and downpipe area. An easy way to rectify this is simply to double it up with an additional cable! Plus it’s possible to also route it further from the heat areas too, or simply heat wrap it. James ripped out my meagre wiring and installed some quality heavy duty cable with substantial connectors. Instantly the battery voltage leaped up to exactly what was being measured direct at the alternator!


The new wiring helped the Cossie produce an impressive 460bhp

The new wiring helped the Cossie produce an impressive 460bhp


With the wiring complete and fully checked for any issues all was well, and the next stage was to get it booked in for mapping. Motorsport Developments in Blackpool need very little introduction, especially for Cosworth owners. Along with their huge stock and able staff, the dyno facility is quite possibly one of the finest in the country. A state-of-the-art 4wd Dyno Dynamics rolling road housed in an impressive custom-built cell with unbelievably good soundproofing and atmospheric consistency! This is largely down to the powerful three stage cooling system for the engine, exhaust extraction, and even the entire surrounding air in the cell, which is exchanged every 4-5 seconds. It’s basically a rolling road in a wind tunnel!

This is no rush job, so before the car is run up to speed it’s plugged into an emulator to allow instant map changes in real time, and hooked up to monitor every parameter the ECU sees and more.

Any issues that arise are dealt with as quickly as possible, as nobody wants to go home empty handed! In my case it was known that a new set of plugs would be needed after a sooty and rich running-in period on a base map. With a suitable trial map for the new spec uploaded the car was performing well, but it soon became apparent that the actuator on the new T38 was actually only a -31 model so a -34 was quickly fitted for a higher base level of boost.

As the runs continued and the boost and fuelling slowly increased it soon became clear that for a change everything was going well! So good in fact that the car actually broke their records for the best power ever achieved on grey injectors. A staggering 460bhp without the injectors anywhere near full duty!

This output is of course down to the recent headwork, cam and larger inlet that the new engine received, but the unanimous verdict was that the now excellent voltage had truly made the most of the whole package. Stewart commented on how many similarly specced cars can’t crack 400bhp due to the electrical problems, and my Saph would have been even less with its previous wiring!



Finally the Saph is both powerful and reliable!


So after five years of constantly chasing power and hunting down problems the Sapphire is finally there! In the beginning I would have never imagined that electrics could cause such havoc and disaster, or been the backbone of real results. Even the difference between the standard of re-wiring can result in dramatically different results depending on how it has been carried out.

So if you want to avoid poor mpg, low bhp, melted components, engine fires, destroyed engines and a dodgy credit rating you now know exactly who you should be talking to and what work you should be having done! I’ve learned my lessons the hard way, but thankfully for you I’m here to pass on my advice so hopefully you can avoid all the dramas I’ve endured and head straight for the good bits – enjoying a fast, reliable Cossie! And trust me, it’s worth every penny – nothing can make you smile like a well-tuned Cosworth!