Retrofit Flasher debug

Big snip.

Actually, it isn't. From my new understanding of how the unit works, the heater operates on a beam which bends, and which then closes a contact to send power to the external lights, and also operates a separate contact that closes and sends power separately to the pilot light. This bypasses the eternal lights' circuit completely, but is dependent on it's action. So if there is sufficient power available, then any pilot light, within reason, should work. I was surprised as well, but the PCB units may not be so tolerant, they are the ones with odd faults that have no logic to them. But I would probably have suspected the same as you until I took a Lucas unit apart and analysed the way it works. When I think about it, I'll measure the current draw by the two different pilot lamps, and work out their wattage. One day..... It is also quite possible that there is more than one model of Lucas flasher unit, with different internal arrangements. What happens if you add a trailer's lights to a car, do you need a different flasher unit? i did once, many, many moons ago, (c. 1972/3), and I don't remember if I needed to modify the flasher. I do know that the lights all worked. the car was my much-loved Herald 13/60, it didn't mind the car-carrying trailer at all.

My replacement croc. clip jumpers arrived this afternoon, courtesy of Mr. Besos.

You have the advantage of seeing inside the unit while I only have a picture in my head based on a description. That said, this is how I picture it.

There is a high resistance connection between B and L, so that the current is not high enough to light the indicator bulbs but it is high enough to heat the high resistance connection. What you call a beam is actually a bimetal strip. The two metals have different rates of expansion from heat, so that when heated the outside metal expands more than the inside metal and the strip therefore bends and makes a contact. This strip is heated by the high resistance wire until it bends enough to make the contact between B and L into a low resistance connection and the indicator bulbs light. It also makes a contact between B and P.

At that time the high resistance wire and the bimetal strip share the current, in inverse proportion to the resistances. There will be some heating from the current flow, but not enough through the high resistance wire to keep the bimetal strip connecting B to L and P. The indicators go out, the high resistance connection starts to heat up and the cycle repeats.

Note that the value of the bulb connected to P will affect the total amount of current flowing through the unit and that will affect the time that the indicator lights are on. Too high a value for the bulb connected to P will result in a longer ON compared to the OFF. For that reason, some flasher units are shown as 21W+21W+5W as the maximum load it is designed for. You also have to bear in mind that the bulb that is connected to the P terminal is on the dashboard, and you don't want it to be distractingly bright when you indicate at night.

There are a different range of flashers for cars that can tow a trailer. They have two sets of internals, so that if there is no trailer the unit works like the standard flasher unit, and if there is a trailer being towed the unit also drives the trailer indicators, and there has to be a second P terminal for a mandatory extra dashboard indicator to show that the trailer indicators are working. Normally the flasher unit would be replaced as part of the wiring for the trailer connector at the back of the car.

For a while, I owned a Ford Granada and that was wired differently again. The flasher unit operated left and right relays, and the indicators were wired via the relays. The positives from this arrangement was that the load provided to the flasher unit by the relay was constant so it made no difference to the flasher unit whether there was a trailer wired in or not, and the Hazard Flash switch simply drove both relays instead of the indicator switch choosing left or right or neither. The negative was that there was nothing to warn the driver if any of the indicator bulbs failed.

Jim

At this point, there is now a direct connection from the input terminal to the output terminal, so the current flow through the heating coil is basically zero.

But the current flowing through to the P terminal does not go anywhere near the heating coil, it passes directly from the input to the P terminal via the auxiliary switched connection. It is also physically nowhere near the heating coil, so I don't see how it will affect the duration of the 'ON' period. This is also why the lack of a pilot light bulb will not prevent the flasher from operating.

If it's too bright, then it's easy to dim it with some film!

The power comes in at the B terminal. In order to get to the P terminal the current has to go along the bimetal strip, and for part of that (the bit that goes to the L terminal) the bimetal strip and the heating coil share the current and the bit from the L terminal to the P terminal the current only uses the bimetal strip. If there is no bulb on the P terminal, the current doesn't go to it. (Electricity flow is quite a complicated subject!)

As for being able to dim a too bright bulb, yes foil will do it but it is better to use the right value bulb instead.

Jim

Sorry, on the unit I have, the power to the P terminal is fed directly to it from the B terminal, it completely bypasses the heating system. It is connected by a separate feed, operated by the same mechanism that makes the B-P connection, but not part of it. Call it a slave connection, to the master that feeds the L terminal.

Agreed.

Re: Your earlier comment about some flashers having a designation such as: "21W+21W+5W", this unit, as described above, has no mention of a pilot Wattage limit. I can only conclude that there are different units, some built the way you describe, but not all.

Addendum: I see those markings on the other, PCB-based units, and it does look as though the circuitry can be damaged. But my Lucas one happily worked, on test, with both types of available pilot lights, whereas the others would, in the car, sometimes work with one type, then not with the other type, and then not with the first type.

You have the advantage of looking inside the unit and seeing exactly what is fitted. Taking your description, then I agree that the bulb used on the P connection can't influence the timing.

Jim