by Richard Ippoliti
AHSTC North Jersey Region
June 2008

I own a 1959 100-6 BN4 that was in need of a wiring upgrade.  I knew that I had a short somewhere in the harness as one of my signal lamps was not working properly (flasher flashing too rapidly) and the entire harness was pretty ratty.  However, when I experienced a short in the plate lamp and the short burned off almost 3 feet of insulation I knew it was time to take action.  I was somewhat hesitant to undertake the task myself but felt that there is no better way to understand what you have than to jump into a project and see it to completion.  Besides, I felt that there are enough members in the AHSTC that I am sure would be more than willing to give me a hand should I need it.  So let me take you on a journey that took about 40 hours on and off over a period of 2 weeks.

Shopping Around
My first step was to shop around for a replacement harness.  I checked out the catalogues from the usual suspects like Moss, Healey Surgeons, Victoria British and British Wiring (BW).  Before contacting anyone I pulled some information off of the internet to understand exactly what needed to be ordered.  The Victoria British and British Wiring web sites provided good information on the harnesses but I found the BW site was more detailed in that it was specific to each model Healey.  I also spoke to some colleagues and found that British Wiring had a good reputation for a quality product.  So I chose BW and I found them to be very cooperative and patient despite all of my phone calls.

Preparation

1. Before the new harness arrived, my first step was to create an enlargement of the wiring schematic that would be used as a reference as I began installing the harness.  I redrew the wiring schematic into a 20 by 30 inch diagram insuring that each wire carried the correct color code number assignment.
2. Once I received the harness, I unpacked each component of the harness and laid them out on the floor to get a sense of how it went together; main harness to rear, rear to tail brake lights, main to front, etc.
3. This next step took a lot of time, but I feel it was the most productive step in the entire process; with wiring diagram in hand and my trusty volt-ohmmeter I proceeded to verify and label the connection points of every wire in the harness.  When compete I knew where every wire originated and terminated and where harnesses connected to each other. (I know some of you will say just follow the color codes and you should be ok).  This process picked up a wiring modification for one connection such that I had BW go back to the engineers in England for verification.  So my diligence paid off.  I also found that the BW harness color coding was right on target.
4. To be complete the harness requires single and double electrical connectors not provided (about 10), new wiring clips and new grommets.  To determine how many connectors I needed, I laid the harness out on the floor again and with all wires labeled, I could establish where a connector was required.  I also ordered the new grommets and wiring clips.

Where to Begin
I guess you can start anywhere, but I decided to work from the back to the front since the wiring here is pretty basic. Before starting any work, disconnect the battery.   By the way, I should state that because of other work being done, the engine in my car was pulled out (this is another story).  This made the work up front a lot easier. 

As I replaced each wire, I put a red dot at both ends of the wire on the enlarged schematic.  So when I was done, I knew everything was connected and accounted for.

1. I started with the rear light harness by clipping the leads to each lamp leaving a pigtail to verify color codes.  Replacement required removing the lamps to gain access to the connections.  Each wire was removed and the new one soldered to the bullet connector and re-installed.  As each lamp was completed, it was reassembled.  When complete, I had replaced wires to each brake/tail lamps, battery master switch, fuel pump and fuel gauge sending unit.
2. The brake/tail lamp harness connects to a harness that runs through the left side of the rear fire wall, underneath the car along the left side rail and connects to the main harness in the engine compartment.  Reminder:  don’t forget to install the new grommets where the harness goes through a firewall before making connections. 
3. Once in the engine compartment I worked the right and left sides of the main harness clipping pigtails and replacing wires and clips. It is somewhat awkward getting to the headlamp harness and pigtails, but just take your time.  With the engine out it saved me a lot of work of having to remove the grill assembly to get to the harness and clips that run across the front of the engine compartment. 
4. This next step was the point of no return; cutting the main harness going into the dash.  Same processes as before; cut and leave pigtails off each gauge and switch and with each wire labeled to where it connects the job went smoothly.  All the gauges, switches and lamps were accounted for (no wires left over), in addition to the wiper motor, high beam switch and heater motor.

Save the old harness for spare parts.  The picture below shows what you end up with when the job is done.

Checking Your Work
I reinstalled the battery with the intention of finding out how I did.  I knew that once I turned the key on, I would start pumping fuel so I had a container ready to catch the fuel.  I turned the key on and the fuel pump worked, the fuel gauge worked, I had lights and high beams.  That is where I stopped as the container was filling up with fuel and I did not want to waste it.  (I have since learned that by plugging the fuel line it will stop pumping once it meets some resistance).  Well I continued verifying my work and as it turned out, I had one error.  The last thing I wired up was the wiper motor.  It was here that I found I had reversed two wires of very similar color; Black with Green and Green with Black.  It was getting late and I was at the end of my day.  Anyhow, I fixed this error with little trouble right at the firewall.  Job completed.