GM HEI circa 1985 info needed

[Stowe, Ted-SEA]

hi, I am working on building a mutant Lucas/gm distributor for my mg tbi
project.

I have a '85 tbi system from a sunbird, which uses a HEI distributor.

I have the matching GM ignition module which would of gone into that set-up.
and I have a Lucas distributor which uses a hall effect sensor, which fits
into my block.

my problem is that the Lucas sensor has a 3 wires coming out of it, whereas
the gm hall effect sensor uses 2. the gm system looks pretty simple
actually. so I am trying to figure out why the pommys used 3 wires. one
might be a ground ? or center tap ??

I suppose I could hook it up on a bench with a coil and work on combinations
until I zap myself.
but I don't want to blow the module nor the sensor in the distributor. and
without the ECU attached I don't know if that would work anyway ??

also I get the idea that the ECU controlled all of the timing, so I would
just take out the mechanical advance in the distributor and lock down the
top plate ??

and would this module fire off an external coil ok, as opposed to the built
in GM coil ?

and I see that the gm module has a heat sink area, something I have to work
on, how much heat did that module put out ?

thanks for your always excellent advice.

Ted Stowe