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In the early 60's, the Thunderbird with the sequential turn signals was all the rage. I had a 1960 Chevrolet Impala Convertible, and wanted to put in sequential turn signals. The tail lights had three lenses, the center one was clear for the back up lights, but would accept a red lens too.  So as far as the lights themselves I was all set. I went to the Ford dealer and asked at the parts counter for the turn signal blinker for the Thunderbird. As I was young and naive, I imagine that I thought I would simply connect it the same way it was done in the Thunderbird. Well of course no such luck, and the part was not returnable as it was an electrical part. So here is the short version of what I did, without any schematics, I too am 72 years old and this goes back 60 years or so.

The Thunderbird turn signal device consisted of a small motor to turn four cams. Three of the cams were used to light the lamps in the proper sequence and the fourth cam was used to keep the motor running until it returned to the home position. Somewhat like the windshield wipers on a car. I removed the standard turn signal blinker and placed a short across it, so that when ever the turn signal was on, I had power there for the entire time. The signal to the rear lamps was now either steady brake or steady turn signal. Of course this was not very useful for this application. However, the front turn signal lamps only have either steady power when the turn signal is on and zero power regardless of the brake switch. Exactly what I was looking for. I used the front turn signal to power the motor with one cam connected, to keep it running to the home position after the turn signal power was removed because the switch had returned to the off position. Now my only problem was to get brake power to the lamps when the brakes were applied and turn signal power for the three cams when it wasn't.

The simple solution to this was to simply use a multiple contact relay, one set of contacts for each lamp. The front turn signal power along with the power from the fourth return home cam was used to energize the relay. Of course I needed two relays, one for the left side and a second one for the right side. It worked as expected and I was the envy of the town, because I was the only non ford vehicle with the cool sequential turn signals. The whole mechanism fit inside of a plastic box about the size of a shoe box.

So that was the solution almost 60 years ago.  Today I would still remove the standard turn signal blinker, and place a short across the terminals to give me always on power when ever the turn signal is activated. I would still use the front indicator to tell me when the turn signal is activated, thus separating the brake signal. From there, I would either use some relay logic, or perhaps discrete logic, along with some timer circuits (555 comes to mind) or a microprocessor to generate the the necessary rear sequential signals. My choice would be a microprocessor, today they are very easy to use and program.

If the only input signal that you have is the 12V to the tail lights, you can't get there from here, for the scenarios that you describe, no matter how much "programming" you do or logic circuitry you design. You need to know the state of the brake pedal switch, turn signal switch and the hazard lights switch at their source and not modulated by the vehicle flasher module, which may be wired upstream of the switches.

Consider this scenario using only the 12V tail light signal:

1. At the first 12V tail light signal - All bulbs ON immediately. (any delay could get you rear ended if it is brakes or a quick lane change)
2. If the 12V goes OFF and then back ON within a time calibrated to the vehicle flasher module rate, then sequence bulbs #2 and #3 ON after delays. Use the 12V signal directly so they go OFF when it goes OFF.
3. If the 12V stays OFF for greater than 2x or less than 0.5x the flasher rate, reset the circuit and go back to step 1 .

This scenario should work in all cases except where you are pumping the brakes old school on ice at a rate that matches the flasher. Hopefully , a rare situation. This should be a fairly straight forward logic circuit with RC time constants and comparators or 555 timer ICs. Use pass-through for bulb #1 and relays for bulbs #2 and #3 on the normally closed (NC) contacts, so that a failure of your circuit still gets the 12V signal to the bulbs. (Fun Fact: Basic automotive flasher modules use current draw to determine blink rate. Which is why it blinks faster when you pull a trailer due to the extra bulbs. There are "heavy duty" modules that set the rate independent of current draw and are a direct replacement for most applications.) You will need the "heavy duty" one for your vehicle to get a stable rate to calibrate your circuit.

I used to own a 1972 Mercury Cougar with sequencing tail lights. Maybe you could get the control module from a junk yard. (All models 1973 and older - I don't know about newer).

I am not completely sure how you want the lights to act when the brake petal is pressed, and frankly I would use a PIC style device to implement this, either a basic PIC chip or one of the ones with a higher level programming language pre-loaded (Ardunio, etc).

But you want a way that does not use code. One way to do this would be to use the old standby 555 timer chip. They can be configured as a one shot, time delay device. You can chain several of them in a ring so that each will trigger the next one in the loop. So they will form a ring counter type circuit.

Then, the first 555 will have a steering diode connected to it’s output and then to the base or gate of a power transistor which drives the first bulb.

The second one has two steering diodes and they are connected to the base or gate of the first AND second power transistor.

The third 555 will have diodes that drive three such power transistors. Each of the power transistors is connected to one of the lamps. So when the first timer is triggered, the first bulb comes on. When the second timer is triggered, the first and second bulbs come on, and when the third timer is triggered, all three bulbs will light.

If you only want one light on for each step in the cycle, just eliminate some of the steering diodes. Additional steering diodes can be connected to the power transistors to activate them when the brake petal is pressed. Additional buffer amplifiers may be needed to get the polarity and current correct for this, depending on the vehicle’s system. The steering diodes will isolate the two functions, brake and directional signals. This does not allow turn signals to flash while the brake pedal is pressed.

An additional, exclusive OR circuit (CMOS logic chip) could be added between the steering diodes on each power transistor and the base or gate of the transistor. This would allow all three bulbs to light when the brake petal is pressed and then they would turn off one at a time if the turn signal is activated.

If this is done, then it would be best to use my suggested method for having only one bulb lit at a time by the turn signal circuit. Thus at least two bulbs would be lit when the brake petal is pressed.
You need to consider how to kill the lights when the turn signal is turned off. This could probably be done by adding three additional transistors to ground the timing capacitors of each 555 when the turn signal is turned off.

I can’t visualise exactly why you would want to do this since, on a car, they are discrete circuits. Perhaps it’s for a model? No matter.

You seem to have cracked how to flash and how to sequence the lamps. The problem seems to revolve around cross connection interference.

Have you tried isolating the circuit’s outputs by feeding the bulb through isolation diodes? With a 12V circuit, these won’t be noticeable, and allow the bulb(s) to be earthed as is normal practice. (Remember to select the diode to handle the inlet surge current through the cold bulb(s).)

You might not want to hear this, but the easiest, most expedient way to do this is with one of the cheap Arduino boards available from eBay. There are a myriad of power supplies, (12 VDC to 5 VDC DC-DC converters), and I/O boards, (relay or solid state), which will just plug together with, as they call them, Dupont cables. All of these are cheap, as in a few dollars. The Arduino IDE is free and with the most of the boards, a simple USB cable is all that is required to interface.

Now, while this may seem very complicated, there are tons of online tutorials. The end result is you get to learn something about electronics, programming, and maybe a new hobby.

The other plus is that you can end up solving your problem AND you also have the ability to make your lights do anything you want.

I found a $20 flasher module via a Web search for “turn signal light sequencer.” The device will flash as many as four lights. You’ll need one module for the left-side lights and another for the right-side lamps.

Creating your own controller with simple logic circuits would get complicated because only one signal turns a brake or turn light on or off. Thus, your circuit must distinguish between a constantly-on signal for braking and pulses for turning. You could use a small PIC microcontroller, but you don’t want to learn how to program, which I understand.

If you change your mind and want to start simply, look at the Parallax Propeller FLiP Module (or the Propeller QuickStart board) and use the free BlocklyProp programming tool. It doesn’t get any easier — you simply choose graphical “blocks” and stack them one on the other. Concentrate on the problem and let BlocklyProp create the code to program the chip.