Installing a New Wiring Harness (Part 2)

By John Trifari

Originally published in the Austin-Healey Magazine, July 1995


Last month I discussed some of my experiences removing the old wiring harness in my 1955 BN1. Here are some thoughts about putting in a new one. Make sure the battery is disconnected.


First, note that the BN1 has a number of harnesses: There’s a two-piece main harness that runs through the engine bay and feeds the dash, a harness in the trunk, and a harness that runs alongside the frame connecting the main and trunk wiring. There are also two headlight “pigtail” harnesses, a small harness to the dipswitch, a harness for the trafficator and the overdrive harness. I purchased the two-piece main harness and the OD harness from British Wiring in Olympia Fields IL. Earlier I had also made up a connecting harness and installed trunk and trafficator harnesses. The headlight pigtail harnesses were inspected and retained, as was part of the original harness to the dip switch.


I started from the outside in by running the dash panel wires of the primary main harness into the cockpit from the engine bay through the large hole in the firewall under the holes for the water heater tubes. The harness went in as far as the pre-installed grommet. Working in the engine bay, I then mounted down the primary main harness branch that goes to the generator and coil from the point where the harness enters the cockpit. This branch runs along the passenger-side firewall and down the right-hand frame rail, under the regulator and over the air-control valve (see photo on page B5 of the Service Manual). I replaced the metal clips with nylon ones as I went along. All directions are defined as facing forward.


Next was the left-hand branch. This runs along the firewall below the fuse bloc and below the OD switch and behind the switch control rod. Then it passes over the steering column and turns down the left-hand frame rail to the direction relay. Wires coming off the harness at this point link to terminals #2 and #6 on the direction indicator relay on the left-hand fender wall and to the relay ground. The harness continues up the forward side of the relay to the left and right front lights. Tip: install the left hand branch of the primary main harness before you remount the OD switch on the firewall Also tuck the short loomed portion of the harness that links to the connecting harness under the switch control rod before screwing down the switch.


Next I hooked the primary main harness to the front lights. My decision to retain the existing headlight pigtails with their monochromatic brown/black covering caused problems at this point, however, and to insure that the primary main harness was connected properly to the pigtails, I had to spend some time sorting out wires. I used an ohmmeter for continuity checks on those wires I could access, guessed the rest and changed connections around later after connecting the battery and after the light switch had been hooked up.


With the primary branch fastened into the engine bay and the firewall grommet in place, I installed the secondary harness. This connects to the primary branch of the main harness next to the direction indicator relay through a green wire (power to the trafficator) and a brown with green wire(horns). It also connects to relay terminals #1, #3, #4, #5, #7 and #8. Tip: put the secondary harness under the primary main harness below the relay. Connect wires from the secondary harness to relay terminals #5, #7 and #8 before connecting the primary harness to terminal #6. The secondary harness drops down to the front cross piece where two short leads connect the left and right rear directionals to the harness that runs to the trunk. I didn’t worry about which wire (left or right directional) was which. I switched the connections at the other end where the connecting harness hooks to the trunk harness by the left-hand rear bumper support.


Halfway across the front frame cross member is the connection to the trafficator harness. It mounts in front of the frame cross piece, and is exposed to the elements as are the connections to the trafficator harness. To protect the harness I covered this section of it with black 3/8” flex cable tied down with cable ties. (Note that power to the trafficator is through a green wire. Power to the right hand directionals is through a green/yellow wire, and it is easy to confuse the two. If your right-hand directionals don’t work, try switching the connections where the trafficator harness connects to the secondary main harness.) Finally, make the horn connections and connect up the brake switch at the far, right-hand end of the secondary harness.



Once the primary and secondary main harnesses were in place, I went back and connected the harness to the fuse bloc. Tip: Note that two white wires run into fuse terminal A3. One of these is the power feed from the ignition; the other (the thinner wire) is the feed out to the fuel pump. I left this wire disconnected until the very last, well after the engine had been reinstalled and the carbs set up. In that way I could run tests of the electrics as I went along without dumping gas on the garage floor. Next I connected the primary harness to the connecting harness where it pokes up through a bracket on the firewall near the fuse bloc. There are four connections here—running lights, fuel pump, fuel gauge sending unit and coil cut-out.


Near this same point, wires exit the harness for the dip switch pigtail. This small harness runs

under the steering column, under the left-hand frame rail and down to the dip switch. The main feed (blue) connects to the center pole of the dip switch. The high-beams (blue with white) connect to the far pole; the low beams (blue with red) to the near pole. Hook up the regulator and the firewall OD switch (black ground line attaches to the lower switch terminal), reconnect the flasher and run the windshield wiper control wires back through the firewall. Now crawl under the dash.


Under the dash


Installation here is also fairly straight forward. The main harness branch runs up the right hand side of the steering column and through a large metal clip. A smaller branch at the end runs across to the starter and wiper switch; another over to the overdrive switch. Another small segment branches from the primary harness just at the point it enters the cockpit and connects to the overdrive relays. It’s a good idea to have these harnesses positioned and are properly supported before you start hooking things up. I ignored this lesson and had to undo a lot of under-dash connections before I got it right.


When all the harness ends are where they should be, start reconnecting the dash. I started with the hard part first—the starter switch. This switch has to be installed in the dash from the front and tightened down from the back before the wires are connected. Tighten down the switch with a Whitworth wrench and put the wires into the screw-down terminals. For best results, do not solder up the wire ends first. Next I re-installed the safety gauge. Then I hooked up the light switch, inserting an in-line fuse between switch terminal Sl and the red line that leads to the front and rear running lights. Then I installed the ignition switch. Take a look at the wiring diagram and you’ll see a short connection between lighting switch terminal A and the hot side of the ignition. This doesn’t come with the harness, so make your own.


With these connections in place, we can start checking the progress of our work. Screw the battery cable end firmly to the brown wire that leads to terminal A of the regulator and insulate the connection with electrical tape. Check for any loose ends, insert two fuses and reconnect the battery. Make sure first that you can get to a battery connection fast if you see any smoke or if something appears to be going wrong. You will be able to check out the lights, directionals, horn and brake lamp. Assuming everything checks out, disconnect the battery, install the wiper and overdrive switches, hook up the speedo and tach and connect the warning lights, put in the panel switch and gauge lights, and install the fuel gauge. Finally I connected the new overdrive harness to the relays off-line, then installed the wiring and relays as a unit and connected it to the main harness. I guess this would be the time to install the heater, but I didn’t have to face that problem. Happy harnessing.


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