Wiring loom replacement project

[mrscalex]

Well after a couple of false starts the project has now started in earnest.

Story so far:

• 2.2 bought as a project with damaged wiring loom
• Caused by boot loom of doom
• Short circuit. Fuse blew. Fuse replaced with cheap Chinese fuse. Fuse didn't blow next time and loom heated up and melted in various places. Absolutely no damage to rest of car thankfully
• Original plan was to let repair sections in but on inspection I gave up at 80 points of damage. In the end it wasn't the soldering work it was the risk of leaving some damage undetected
• In between time I had an auto electrician in who was adamant without seeing the interior out that he would repair it. He didn't even want to use colour coded cables. He wanted to do everything in red... needless to say I didn't bother using him. He could have left me with a potentially lethal car
• Considered using second-hand loom. But this is a major job and I felt it could only be done properly with a new loom
• New loom purchased for what I think was a very reasonable £850 from Cotswold BMW. Which is where the story picks up.

First a couple of pics of why I abandoned the idea of repairing the existing loom. This is part way through inspection. Each compromised part of the loom was tagged with a cable-tie. It ended up with around 80.

What I suspect was the seat of the short circuit. The interior boot light cabling. Or what's left of it.

A typical area of knock-on damage once the original cabling/circuit heated up when the fuse didn't blow.

The damage went all the way up to the fuse box.

I'll catch things up over the next few days. Suffice to say the project is progressing positively so far - weather and daylight permitting.

 

[mrscalex]

The offending fuse that never blew. Although the plastic melted around it...

 

[Dino D]

Well that looks familiar...

 

[mrscalex]

Well that looks familiar...

I thought you may say that

 

[Dino D]

I thought you may say that

I prefer to NOT recall that period of ownership!

Looks like you have your work cutout for you there. You’ll not want to eat spaghetti for a while after this job

 

[mrscalex]

We’re actually loving doing this. As long as you think and plan it’s much nicer than being under a car removing stuck fixings, scraping your knuckles and getting filthy.

But we’ll see if I’m still saying that when we’re finished and we test it all!

 

[mrscalex]

This is how the loom arrives. The box is the same sort of size that a hoover might be packed in.

And here it is out the box ready for planning how we get it in.

Note the fuse box comes with the loom and is in fact integral to the whole thing.

Each of the discrete legs is neatly tied together with a rubber bungee.

I’ve removed a loom whole before and it’s a lot more unruly than this! In fact BMW have planned this as a spare part very well and given the very best chance to get this installed in an organised manner.

 

[mrscalex]

We'd already decided on the basic strategy. Chop as much of the old loom out as possible while leaving all connectors in situ with 6-9 inches of cable attached. That way we could see what needed connecting back up from the new loom and with what connector.

There was no point trying to keep the old loom whole anyway - it was after all knackered!

There are various spare connectors on a Z3 and taking this approach will hopefully avoid scratching our heads over these.

We also took loads of photos before any stripping out.

The main concern with running the loom around the car was whether we could pass the driver side behind the heater matrix without taking it out. We felt we should give it a go after seeing the loom laid out.

Here's the first section chopped out. It's the section that runs under the passenger seat.

And here's the trainee engineer cutting the section that runs behind the heater matrix at a point near to where it goes through the bulkhead to the fuse box.

The loom at this point is as thick as your wrist.The thick red cable is one of the two battery positives. This one is the main feed for the car and is bundled into the loom itself. It's way too thick to cut with wire cutters. So we'll hacksaw it. The other battery positive (not here - driver side) goes straight to the starter and is separate to the main loom. We won't be changing that.

After cutting the battery positive that left the passenger footwell looking like this.

 

[mrscalex]

Next up was to get the old fuse box out. We needed to cut one more big bundle and that's the one that runs up to the rack with the ZKE and other modules that lives behind the glove box. We also cut a number of individual cables (including earths) and smaller bundles up under the passenger dash including the door loom connector

The fuse box is held in place with 4 screws inserted from the footwell side.

It came out easily although there are some engine bay connections that also need to be cut. These include the diagnostics port, front panel leg (headlamps etc) and the alarm siren.

This leaves the inside of the car looking quite empty now.

 

[mrscalex]

With the old fuse box out and space created in the passenger footwell, it was time to start installing the new loom.

The entire loom, excluding the legs to the engine bay, needs to pass through that hole in the bulkhead we can see in that last photo. And here it is from the engine bay, the direction we are going in.

We laid a sheet over the engine to protect engine and new loom.

And laid the harness onto the sheet.

And then started feeding it through. Well either that or a snake has got into the engine bay!

Getting there.

And almost done.

And here we are with the fuse box all the way in. Getting the 4 screws back in to secure it was our first nightmare. The fuse box needs to be aligned perfectly and braced by one person as the other screws it up from inside. Sounds simple but we must have spent an hour on this step.

Here's the loom from inside the car. Everything is still bundled. We haven't needed to undo anything yet. We want to keep it like that until we actually need to start routing the loom. It's going to get tangled quick otherwise.

 

[mrscalex]

Our time was running out for that day. But we wanted to see first if we could get the loom behind the heater matrix before we packed up. It was our big concern.

First of all we pulled the remnants of the old loom out from passenger side into the driver side.

That allowed us to see what space we had to play with. Not much - maybe 2.5"x2.5". It looks more here but it really isn't. Note the cable ties. We want everything restored to how it left the factory. Plus it could be dangerous not to support the loom properly. It will be much easier to get the cable ties on now than after the loom has gone through.

And the answer is yes! It can just be done. Here it is pulled through and supported under the driver's side dash.

We're happy with where we've got to and call it a day.

 

[Althulas]

That’s great progress so far and a relief that you could get the loom around the heater matrix. It’s pretty neat the loom coming pre wired into a fuse box. That would have been a nightmare and head scratchingly time consuming to wire up on its own. So far you both have made the job look methodically simple. I look forward to the next update and hope rest goes so well.

 

[Jack Ratt]

Great work mate, I'm usually up for a mechanical / spanner job but there's not much chance of me being confident enough to tackle a job like that. You've both earned a beer after that, so here's a couple each

 

[Dino D]

You make it look easy!

Leaving the connectors in place is a great idea so it’s essentially ‘plug and play’ without headscratching about what goes where!

 

[mrscalex]

It’s pretty neat the loom coming pre wired into a fuse box. That would have been a nightmare and head scratchingly time consuming to wire up on its own.

You got it in one. I didn't imagine for one minute it was going to come with the fuse box. But as soon as I saw it in the box I was over the moon as the only part I was dreading was feeding all the connectors up into one tight space.

I've removed a complete loom from a breaker before but did it the other way round. I removed the connectors from the fuse box casing and withdrew the loom into the cabin. The whole thing is a nasty tangle - not least the fuse box end.

 

[mrscalex]

You make it look easy!

Leaving the connectors in place is a great idea so it’s essentially ‘plug and play’ without headscratching about what goes where!

I think that's going to pay back best when I do the driver dash. That's the highest concentration of connections on the car.

In that area I've cut the loom further back along leaving much more. That's partly because it's easier to do like that due to access and partly because I want to retain the routing of the loom bundle and how it's clipped. It's not really possible to get photos in that area like I have the rest of the car before chopping out.

 

[Geophys]

My father was an automobile electrician all his working life, his father started the business in 1912 changing London Taxis from acetylene lighting to electric lights so I grew up in a garage where new looms were fitted, he would usually make up the loom himself on a pin wall. Looking at that loom, I think he would have taken early retirement! Very brave, but a very impressive job so far.

 

[Dino D]

My father was an automobile electrician all his working life, his father started the business in 1912 changing London Taxis from acetylene lighting to electric lights so I grew up in a garage where new looms were fitted, he would usually make up the loom himself on a pin wall. Looking at that loom, I think he would have taken early retirement! Very brave, but a very impressive job so far.

It’s scary how many wires are on such a small ‘low tech’ Z3. I was shocked when I looked under there!

Can you imagine how many wires go into a new 5 or 7 series!!!

Not many places interested in doing this sort of work these days that’s for sure.

 

[mrscalex]

It’s scary how many wires are on such a small ‘low tech’ Z3. I was shocked when I looked under there!

Can you imagine how many wires go into a new 5 or 7 series!!!

Not many places interested in doing this sort of work these days that’s for sure.

Funnily enough James said to me hey Dad would you fancy doing this on our 3 Series? Already knowing the answer...

It’s probably the nastiest job possible to find the right garage to do.

In a way I don’t see it as an auto electrician’s job. What I’ve not covered is the stripping out of the interior, although I may cover putting it back. And that’s really where you benefit most from knowing your way around.

I think you said it was a 4 day job when you had your’s done. That sounds spot on. 1 day to remove the interior, 2 days on the loom and 1 day to replace the interior.

I’ve hopefully reduced the job to a plug and play one with the approach. Which any diligent garage or mechanic should be able to tackle. Fault finding afterwards should not really need an auto electrician. Just going back and checking everything is plugged back in.

But try and find someone, anyone dilligent enough to route and support the loom correctly. If they don’t problems will return from chaffing etc in years to come.

And I think many of us are more experienced when it comes to pulling interiors in and out. Which is 50% of the job.

 

[Geophys]

It’s scary how many wires are on such a small ‘low tech’ Z3. I was shocked when I looked under there!

Can you imagine how many wires go into a new 5 or 7 series!!!

Not many places interested in doing this sort of work these days that’s for sure.

Even in the 50s and 60s when I was growing up most of my dad's business was trade, if you took your car to any garage in a large chunk of South London with an electrical problem they just brought it over to my dad to fix. The moaning when he took his one week holiday each year was enormous.