First, the 35amp and 50amp English standard original Lucas fuses translate to 17amp and 35amp using fuses available in the US. The difference is in the way they react to a short so reduce the amperage to the US equivalents if that is what you are using. Second, put them in the correct slots on the fuse box as previously mentioned by Greg as you could be applying enough power to you switched circuits easily have them burn .
The original harness wiring is quit thin and never designed to handle the amperage used with today’s headlights, etc. Age and corrosion further deteriorates its flow potential and induces higher resistance resulting in heat and further accelerated oxidation. To address these conditions, I would clean and solder all bullets and install dielectric grease in all connectors before inserting.
Simple Analyzing Tool and Procedure
Before analyzing and/or testing the circuits in question, I would acquire an inexpensive manually-reset Circuit Breaker (with connector) and attach a bullet on both contact wires. A second unit, created from an in-line fuse setup and extra fuses, will also come in handy to isolate a questionable component during testing. As you continue your investigation into the causes of your present problem, disconnect the original connection from the power source and install the circuit breaker in between. If the breaker flips when power is applied, reset the breaker, disconnect all outputs, and test again. If the breaker again flips, the problem is the component. If not, move the breaker to the output circuit and connect the inline fuse unit to the input and test. If the breaker flips, move all to the in-line fuse to the input connector of the next unit and test to see if the breaker flips. If it does and the fuse remains good, the fault is in the line between the switch output and the next component. Using both units allows me to definitively identify the location of the fault validate the correction with at low risk.
I realize this is a tedious task but, without finding something obvious, and not yet having installed fuses to narrow the issue, this is the procedure I have followed with success.
Directory of Fuses
To address this type of issue, I have installed quite a number of in-line fuses to protect all major components/circuits. Although some think I have gone overboard, the smaller the affected domain of an issue, the faster the problem will be identified and fixed. Since in-line fuses can be easily installed, or added over time, into a specific circuit and hidden, I have resorted to creating a fuse directory of function/component/circuit protected, location, and amperage to help jog my memory after years of nothing happening.
Definitely Install Relays
Also, since the original gauge of wire used in the Healey was never designed to handle today’s electrical loads, I have also installed relays to power the headlights, driving lights, horn (yet to be completed), and sound system to with new heavier wiring installed to power these components. Original wiring is not only used to switching the relays and, therefore, carries a significantly lower amperage.
Again, this is the processes I would follow and hope you find your faults very soon. Grounding is an issue often encountered when something doesn’t work and there is no short in the circuit so don’t forget to carefully examine for a bad ground when something doesn’t work.
Good luck,
Ray (64BJ8P1)