There are several principle reasons the head lamp circuit bursts into puffs of smoke on a TR6.

The first reason is the TR6 dash mounted head lamp switch is of inadequate design and is not up to the task of carrying the entire load of the parking lamps and head lamps. This is further aggravated when unwitting owners add any sort of accessory to this circuit, such as higher wattage headlamps, fog lights, driving lights, or other such equipment.

The second reason for the electrical fires is the fact that the actual head lamp circuit is not fuse protected. The wiring comes directly from the battery (smoke storage unit in Lucas electrical theory) to the head lamp switch. The un-fused power is then sent directly to the head lamps. The power for the parking lamps is fused after it leaves the head lamp switch.

The third reason for head lamp circuit problems is poor connection. The junction block on the positive battery cable frequently has corroded and loose terminals that cause problems. Also, poor connections at the lamps themselves (in the lamp connector on the headlamp, in the socket and bullet connectors on the parking lamps) frequently cause one or more lamps to stop or can cause overheated wiring.

Let’s look at a remedy for each situation.

The weak head lamp switch can be overcome by using relays to remove the load from the head lamp switch (see wiring diagram). The relays are installed and wired in a manner so that the entire electrical load passes through the relays, not he head lamp switch. The head lamp switch simply energizes the coils on the relays (which is a very light load), and the relay does the heavy lifting. One relay powers the head lamps and a second relay powers the parking lamps. The switch will never be overloaded if relays are utilized. There is plenty of room behind the dash to locate the relays; mine are mounted to the firewall. You cannot see any screws from under the bonnet because they penetrate the scuttle area and are hidden.

The second problem, lack of fuse protection, can be addressed by adding some protection to the large brown wire coming from the battery. My preference is an automatic reset 30 amp thermal breaker (available at most auto parts stores). The breaker protects the entire circuit and if something does go wrong it will “trip” and remove power from the circuit. After the breaker cools, it will automatically try to reset. The wiring diagram outlines the installation of this breaker. Mine is located in the same area as the relays the power the head lamps and parking lamps.

The third problem, poor connection, can only be addressed some good old-fashioned elbow grease. Clean and tight electrical connections are critical to keeping your system working. Start by checking main feed for the head lamp circuit (located on the junction block attached to the positive battery cable). If the female connector is in poor condition, it can be replaced with a new one. Use some emery cloth or fine sand paper to polish the connections and then apply dielectric grease to the connection during assembly. If the connection is loose, you can tight the connection by squeezing slightly with some needle nose pliers to achieve a tighter fit. Clean and apply dielectric grease to the rest of the system as well, at bullet connectors for the marker lamps, in the marker lamp sockets, and at connections at each head lamp.