Installing a New Wiring Harness (Part 1)

By John Trifari,

Originally published in the Austin-Healey Magazine, June 1995


Earlier this year the engine of the BN1 was pulled for rebuilding, and I got the opportunity to do something I’ve wanted to do for a long time—-install a new wiring harness. Here are some thoughts that might make your first re-wire job go a little more smoothly.


First and foremost, remember that you’re working around electricity and that unprotected loose wires might touch places they shouldn’t, causing sparks, or worse. So: as a general rule, always make sure the battery is disconnected while you’re stringing wire or hooking up switches. Second, if you want to test things as you go along, make sure that the wires that have yet to be connected are safely insulated or connected up, and finally, be sure to have a fire extinguisher handy. You might want to take some pictures of the empty engine bay before you start working. I took a slew of pictures thinking that they would be really helpful in putting the harness back in. But aside from giving me a good before—and after appreciation of all the work I did and for use in this article, I found these pictures to be of only marginal assistance.


More important is the wiring diagram. Learn to love this document, and don’t consider re-wiring the ecr without it. I duplicated mine 31 times—one for each color code used on the wiring. Then I put on my reading glasses and traced out each color circuit. These individual diagrams were really helpful. In this regard, it’s also very helpful to keep in mind how Lucas wires are color-coded:

  • Brown: Unfused (battery) side. The BNI also uses a brown-based scheme for fused wires from the battery circuit (replaced with purple in later cars). Be especially careful around any brown (or purple) wire.

  • White: Unfused from the ignition (e.g. fuel pump).

  • Green: Fused from the ignition. Green is used for accessories such as wipers, and directionals, and for the overdrive.

  • Red: lighting circuits from the light switch. These are unfused.

  • Blue: Headlight circuits (unfused).

  • Yellow: Generator wires.

  • Black: ground.



To begin, I removed the ID plates, regulator, fuse block and directional relay, replacing the mounting screws as I went along. I also removed the safety gauge, pulling the temperature sensor back into the cockpit. The starter solenoid was removed prior to taking out the engine. The OD switch on the firewall was unscrewed and allowed to drop away, but remained connected. Then I climbed into the engine bay with a pair of wire cutters and began chopping out the old wiring up the point where the main trunk of the harness went through the firewall and into the cockpit. Whenever I unscrewed one of the metal loops securing the harness to the body I replaced the screw. All connectors that looked useful were retained: all bullet terminators clipped off for later use. The brake canister remained in place.


Next I went under the dash, cut the wires to the fuel gauge and removed it. The speedo and tach cables had already been taken out when the engine was removed, so all I had to do was cut the overdrive ground and the light leads to remove both gauges. Then came the turn indicator light and all the switches including the ignition, OD, light and starter switches. A set of Whitworth wrenches is invaluable for this work. I also pulled the two overdrive relays from their location below the dash, leaving them temporarily connected to the old overdrive harness.


With this done, I removed all the old wiring under the dash, again saving connectors and bullet-ends. I had thought at first about replacing the wiring as I went along, but over the years everything had turned brown/black, and there was no way that that old harness could have helped me with the new installation, so I just chopped it out. Finally, I removed the heater. This was done for two reasons. First, I never used the heater (I closed the taps a month after I got the car) and I can’t think of anything more useless in a California Healey. Second, the harness enters the cockpit from the engine bay through a hole that is directly below the holes for the heater’s hot water tubes. In short, you won’t be able to install a new harness easily unless the heater is out. To remove it, disconnect the windshield vent tubes and undo one nut from the engine side and two nuts from a bracket that is mounted to the heating/ventilation duct under the dash.


With the car’s central nervous system now taken out, I climbed into the engine compartment and cleaned it up using a combination of Oil Eater and carb cleaner, applying Gunk on trouble spots. I got tired of being stabbed in the back by the choke cable, so I tied it loosely to the hood latch release with a nylon cable tie. Also be careful not to catch yourself on the fuel pipe when facing forward, or on the brake junction on the right hand side of the bay when facing aft. In other words, when you stand up in the engine bay, stand up slow and stand up straight.


All grommets were removed from the firewall—some retained—and rust primer applied in the bayas required. The shroud was then masked off with newspapers, and masking tape was applied from the cockpit side to cover all the holes through the firewall. Also masked off were the oil pressure tube, the end of the fuel pipe, the three-way brake pipe junction on the right hand frame cross member, the clutch linkage and the rubber catch for the hood prop. The harness connecting the engine bay to the trunk was separated from the side of the foot well as was the battery cable, and a coat of primer was sprayed into the bay, followed by a coat of gray engine paint. The brake canister, steering shaft and air vent duct were repainted black. When everything was dry, the bulkhead area was shielded, the under-lip of the dash masked off, masking tape applied to the firewall holes from the engine bay side and the area under the dash sprayed black. Get plenty of fresh air while you’re doing this.


Next month, some thoughts on putting things back together.


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