Go find a suitable grommet on the wrecking yard.
I had to enlarge the hole a bit and use the A4 Starter cable grommet for
my engine conversion:

http://v6bus.de/v6tdi/battneu.jpg

Also, you can use the grommet of an Audi ECU box, and modify your
firewall to get one round grommet side, the other straight (like shown
on the left):
http://v6bus.de/v6tdi/elektrik1.jpg

All pictures taken while "in the making"

regards
Raimund

Am 10.04.2020 um 18:06 schrieb Dan N:
> failed to get a new grommet... I'd suggest doing this..
> Get a bicycle inner tube with right size (rather small), cut a piece about
> 3 or 4", slide it over the harness and position where the hole/grommet is,
> tie it with zip ties on both end and pull the harness thru the hole... if
> needed add another layer.
>
> On Fri, Apr 10, 2020 at 8:57 AM Bruno Walser <bruno.walser@multavista.com>
> wrote:
>
>> I recently replaced my 2.1 WBX with a 2001 ALH TDi engine. With the removal
>> of the old wire  harness I also pulled out the grommet on the firewall
>> where the wire harness goes from the ECU to the engine. I installed the new
>> wire harness and added various additional wires such as the wires to the
>> solar panels. The new ECU is located where the old one was, underneath the
>> rear bench. I was not able to reuse the old grommet. Thus the new wires go
>> now through the fire wall without a grommet and the hole is still partially
>> open. I am still looking for a good way to close up the opening to prevent
>> air-, water, mice etc from getting in?  Good suggestions are very
>> much appreciated? As you all know, the hole is not easily accessible.
>>
>> Thanks
>>
>> Bruno
>>