Bulkhead wiring loom

[jack350]

The interior of my 350i has been stripped out for many years. However lock down gave some time to refurbish. New foam and carpets replaced, wood back from Chapman & Cliff. Time for dash to go back in. Installed the heater box. The loom running from passenger side to drivers, in the middle seems to lie on the back of the heater box? Questions is at passenger side is it fastened / held up against the bulkhead at any point as its quite a weight?

[Penelope Stopit]

Be it originally fastened or not, clip it in as many places as possible to ensure no rubbing created by vibration

[jack350]

Thanks for getting back to me
On the drivers side the loom rests on top of the steering column bracket. Its more the passenger side where a number of fairly bulky looms come together.
I suppose the question was does anyone know where it would have been originally hung / supported from?

[adam quantrill]

That seems to be a common feature. On mine the multiplugs droop down either side of the column (and I occasionally have to fiddle with one if the indicators stop working).

If you're adding supports make sure they are quite broad (e.g. wide releasable tie wraps, maybe with extra sleeving on the tie wrap) so you don't create another place where forces are concentrated and chafing can occur.

[Penelope Stopit]

jack350 said:

Thanks for getting back to me
On the drivers side the loom rests on top of the steering column bracket. Its more the passenger side where a number of fairly bulky looms come together.
I suppose the question was does anyone know where it would have been originally hung / supported from?

Sponge can be placed around the loom if it's resting on something and can't be clipped away from it

This type of pipe insulation works wonders

[adam quantrill]

What about heat though - high current conductors (and especially mythical hidden resistance wire) need to allow air circulation to avoid hot spots especially in summer with under-bonnet temperatures leaching into the bulkhead area. Maybe don't fold the foam round the loom but do put it onto any obstacles and let the loom sit on top.

[jack350]

Thanks to you both
Will take a closer look at the weekend
Whilst on the subject or wiring, I have been checking the wires that go through the A post into the door. There are connectors for the mirror, plus the window motor, but in addition about 4-5 wires, heavier duty ending in a female Molex connector, with nothing it seems to attach them to?

[Penelope Stopit]

adam quantrill said:

What about heat though - high current conductors (and especially mythical hidden resistance wire) need to allow air circulation to avoid hot spots especially in summer with under-bonnet temperatures leaching into the bulkhead area. Maybe don't fold the foam round the loom but do put it onto any obstacles and let the loom sit on top.

Engine harness wiring gets much hotter than any interior wiring and the hot temperatures reached don't cause any problems

No problems can be caused by covering a whole interior car loom with foam or similar materials

Wiring within a vehicles harness doesn't need to breathe

Should a cable overheat in a harness due to a dead short circuit, cables with little oxygen around them will take longer to burn. Hence the more covering around a bundle of cables, less is the oxygen around them and less is their burn rate

jack350, don't be concerned about fully covering any parts of the wiring harness with foam, motor manufacturers use foam for covering wiring harnesses

[Penelope Stopit]

jack350 said:

Thanks to you both
Will take a closer look at the weekend
Whilst on the subject or wiring, I have been checking the wires that go through the A post into the door. There are connectors for the mirror, plus the window motor, but in addition about 4-5 wires, heavier duty ending in a female Molex connector, with nothing it seems to attach them to?

Possibly for central locking?

[adam quantrill]

Penelope Stopit said:

motor manufacturers use foam for covering wiring harnesses

That's fine if it's by design and they have calculated the current derating of the cable when thermally insulated.

However the TVR harness wasn't designed to be insulated in this way (if it was designed at all, but that's another issue...) which is why I raised the point.

[Penelope Stopit]

adam quantrill said:

Penelope Stopit said:

motor manufacturers use foam for covering wiring harnesses

That's fine if it's by design and they have calculated the current derating of the cable when thermally insulated.

However the TVR harness wasn't designed to be insulated in this way (if it was designed at all, but that's another issue...) which is why I raised the point.

Yes you have raised the point

Are you able to show evidence of there being a problem?

The wiring within the cockpit won't reach temperatures high enough for there to be a problem

PVC cable will be good up to 70°C

Are you able to post calculations showing there will be a problem?

[adam quantrill]

Hi Penny, as you've raised that point, and you're proposing a modification, I think the onus would be on you to do the calculations, to prove that it's safe.

[Penelope Stopit]

adam quantrill said:

Hi Penny, as you've raised that point, and you're proposing a modification, I think the onus would be on you to do the calculations, to prove that it's safe.

Wouldn't have posted the method if it could fall over, have already done the calculations in the past and again today

Was hoping that you could break the method of foam covering as it's always good to learn something new