I just finished installing a new harness and have some tips:
--get one of the full-color large size wiring diagrams from Tom's Toys
--get a label maker (such as the Dymo LabelManager 160 $14 on amazon)
--referring to the diagram, label all the wire ends; I had to staple the labels to keep them from separating. You can do this in the comfort of your living room - this minimizes confusion time lying on your back looking up under the dashboard.
--I found it helpful to test the wires for continuity to figure out, for instance, which wire to a switch was the supply side and which was the output side.
--the big stretchy firewall grommet is 281-900. I found the one in the grommet set to be too stiff to stretch over the harness.
--BCS sells complete P-clip sets for the different Healey models for around $80.
--I wound up with an extra set of grommets, which was useful as I ruined a couple of them.
--many of the P-clips are attached to captive 10-32 nuts. Since I wasn't going for concours, I bought a supply of stainless 10-32 screws in 1/2", along with some in 5/8 & 3/4. A supply of #8 and #10 sheet metal screws will see you through. Buy these in bulk from suppliers such as FMW Fasteners or Bolt Depot. Also lots of #10 lockwashers - I like the internal stars.
--since I'm running 5-spd, I removed the O/D wiring, leaving a number of threaded holes in the firewall - plugged with 10-32 SS setscrews
--before installing the heater, make sure the wiring is the way you want it and plug all the air leaks in the firewall
--I made a conduit from 1" thinwall alum. tubing, which runs across the heater plenum behind the heater. This makes it easier to snake accessory wires behind the heater box
Your crimp tool should have the little point at the yellow arrow:
Made a separate harness for grounding the gauge lamps. IMO they're poorly grounded through the mounting clamps: