This information was on a website I found years ago and saved, the original website is no longer available so I am copying and pasting the info here, I hope there are no copyright issues.  The original page was named Fire Pinto.

I also take no responsibility for the information that is on this page, use it at your own risk.

Sequential Turn Signals
How they work...

 First of all, I would like to get you a little familiar with the parts in this system. Even though there is only really 2 different kinds of relays used they all serve a different purpose.

** The Multifunction Switch, Hazard Flasher, and Turn Signal Flasher --
These are existing parts in your car already; I just added them into the diagram so it was easier to see what was happening.

** The Alternate Turn Signal Relay & The Alternate Hazard Relay --
These relays activate opposite of the stock turn signal flasher and hazard flasher. They basically supply power to the Left or Right Selector Relays when the stock flashers are not. Which keeps the selector relays on until you turn off your directionals.

** 4 Diodes --
These prevent back feed of voltage into your vehicles original turn signal circuit.

** L. & R. Selector Relays --
These are basically the "on" switch to the whole system. One side of the relay directs the Stop/Turn circuit to the Main Trigger Relay when the turn signals are on, and to the L. & R. Seq/Std. Select Relays when the brakes are pressed.
The other side turns the power on for the Sequencer Relays, the R. & L. Seq/Std Select Relays, and supplies power to the common terminal of the Alt. Turn Signal & Hazard Relays. Which actually supplies power back to the coil of the L. & R. Selector Relays.

** Sequencer Relays (Bulb 1 - Reset) --
These relays are what actually get the work done. Each relay powers the next one in sequential order. (No kidding, eh) They sequence until the reset relay energizes and removes power from the Bulb 1 Relay. Which removes power from all of the Sequencer Relays. Then the process starts over.

** L. & R. Seq/Std Select Relays --
These do 2 things. They mainly combine the three bulbs into 1 circuit for when the brakes are pressed or when the sequencer is disabled. The other thing is that they keep the power to the sequencer relays from back feeding from the left side to the right side, and the other way around.

One helpful thing to know in understanding this system, is how to make a relay stay "on" with just a "pulse" or closing of a switch or button for a short period of time. The diagram to the left is an example of this setup. Below is a description of how it works.

1. The main power is at the common terminal.
2. When switch one closes, (ven for a split second) it closes the NO contact, supplying power through Switch 2, to the coil.
3. Now the power output is "on"
4. To turn off power output, open switch 2
5. To start over, close Switch 2, and "trigger" switch 1

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