Some notes on constructing new cables compatible with the BC01V:

The following pins are implemented by the W076 at J1:
A        GND
B        GND
E        RX-DATA
F        TX-EIA
H        20MA-INTERLOCK
J        RX-EIA
K        +20MA
M        EIA-INTERLOCK
S        -20MA
V        RTS-EIA
AA       TX+
DD       DTR-EIA
EE       -15V
KK       TX-
PP       RELAY+
TT       VCC
UU       GND
VV       GND

Other interfaces may also provide:
T        CTS-EIA
Z        DSR-EIA
BB       RSD-EIA

E must be jumpered to M for RS-232 input, or H for current loop
input.


For the construction of the cable end, you'll need:
Mouser:
    22-55-2442	44 pin shroud
    16-02-1111	71851 series pins

If you plan to use your cable with vintage gear, you will need
to use a flush cutter to remove the keying tab from the housing.

You will also need a crimping tool compatible with the
71851 series pins.  Mine is an FCI (Framatome Connectors
International), with the 22-24 AWG head preinstalled (stock
number SP1552).  As of this writing (2020), they are available
on eBay for about $27.  It has a clip which roughly positions
the pin, then you insert the wire until it hits the clip and
squeeze the handles, making sure everything stays lined up,
until the ratchet in the handle finally releases.

Be sure you have adjusted to tool to the tightest setting at
which you can operate the ratchet.  (For mine, that's the "8"
position of the allen screw.)  A good crimp must make a gas-
tight connection that will not pull out of the pin.  Both of
these things require physically deforming the conductor.

For our BC01V RS-232 purposes, we need to connect:
    At least one ground.
    TX-EIA and RX-EIA.
    RTS-EIA and DTR-EIA.
    EIA-INTERLOCK and RX-DATA.
We can jumper DTR-EIA to CTS-EIA and DSR-EIA at the far end of
the cable, which simplifies the crimping.

The wire I'm recommending is CAT-5 stranded (24 AWG), as that
is easily available.  DO NOT attempt to use the solid conductor
CAT-5.  It is easier to work with, but WILL FAIL in this
application, which requires the cable ends to flex.

We'll also need a male DB25 or DE9 connector, for the other end
of the cable.  I suggest a male DB25:
    273005	DB25 Male, solder cup
    273031	DB25 plastic hood
and the following adaptor:
    SGC-9M25F	25P Female, 9P Male adapter
I also recommend this null modem, for connecting DTE endpoints
together:
    31D1-28400	DE9 F/F Null Modem
These are all available on eBay (at the moment) for $5, $7, and
$3, respectively.  (You may have to search for "DB9" instead of
"DE9", and look for "null modem", not "gender changer".)  They
are also available locally (to me) at reasonable prices:
https://www.pchcables.com/dbmasocupco.html
https://www.pchcables.com/dbplhoscty.html
https://www.pchcables.com/slmi9pinma251.html
https://www.pchcables.com/db9ffnumomig.html

Strip back a couple of inches of the outer plastic on the CAT-5
cable.

Use a wire stripper to peel off a couple of millimeters (0.1")
of insulation from each conductor.  The bare part should extend
through the contact area, but leave insulation for the two
rearward tabs to crimp onto for strain relief.

Use the crimping tool to attach receptacle pins to each
conductor.  When you have the conductor crimped to the pin,
"square up" the part that covers the insulation, as otherwise
it will likely have ovalized and bind in the shroud.  DO NOT
use solder to attach the recepticle pins!  Doing so creates
a spot where the flexible bit meets the inflexible solder,
and the cable will evenually fail there.

Also, cut off a short length of CAT-5 (an inch or so), and pull
out a color (I used orange), and similarly strip and attach
receptacle pins to both ends.

Note: The header is actually 44 pins, not 40.  If we cared to,
we could block up the four endmost pins with keying pins.
These spots will be under the clip that holds the shroud in,
when the cable is fully seated, and they function to center
the 40 active pin sites, so the connector cannot be inserted
"off by one".

Use the following table to install the pins into the shroud.
Each pin should visibly raise the plastic retention clip as
it enters, and each such clip should "click" back down when
the pin is inserted sufficiently.  Make sure that each pin
is held in by the appropriate retention clip.
Orange-White	GND		A	(aka 40)
Green-White	GND		B	(39)
Jumper     	EIA-INTERLOCK	E and M	(36 and 30)
Orange     	TX-EIA		F	(37)
Green      	RX-EIA		J	(35)
Brown      	RTS-EIA		V	(23)
Brown-White	GND		UU	(2)
Blue   	    	DTR-EIA		DD	(15)
Blue-White 	GND		VV	(1)

Moving to the other end of the cable, I'll assume a "solder cup"
connector.  These are easy, and do not require specialized
tooling.  What they DO require, however, is a shroud or hood
which holds the connector inflexibly relative the cable, and
provide strain relief elsewere, in the flexible part of the
cable.

Choose another jumper wire (I suggest the blue), strip a couple
of millimeters off each wire, and a little extra off the blue,
and one of the striped wires.  Wrap one end the jumper around
the blue wire, and solder it, leaving enough of the end of the 
blue wire to go into a cup.  Similarly, wrap three of the ground
wires around the one you stripped a little extra, preparing the
assembly to go in a cup.  Then solder the pins as follows:
Orange-White	GND		7
Green-White	GND		7
Jumper     	CTS		5
Orange     	TX-EIA		2
Green      	RX-EIA		3
Brown      	RTS-EIA		4
Brown-White 	GND		7
Blue       	DTR-EIA		20
Blue-White	GND		7

If you desire to also connect a jumper from DTR-EIA to DSR-EIA,
the additional jumper will go from the blue wires to pin 6.

Don't forget the to install the cover, or you can expect the
wires to soon break where they meet the solder.  Be sure that
the cable clamp grabs the cable in such a way that the wires
inside the hood cannot be pulled on or jiggled.

That's it for the RS-232 cable!

Vince