Can someone explain the emergency flasher?

[Alfred Lord Tenniscourt]

So I had the turn signal circuitry all figured out, then just to confirm what I thought, I put a meter on the emergency flasher switch. Now I don't know how it works any more... I had figured that one side of the switch would be in series with the brake light circuit, and stay normally closed, and the other two wires would stay normally open in series between the emergency flasher and some wire which would go to the turn signal switch.
I just put a meter on it and the switch is actually normally open between all four wires, then closed between all four wires. It is either four open circuits, or a four wire pigtail! Pardon my abbreviation, but wtf?
Is the switch even working right? I would assume it is because most of the 41 year old stuff in my truck surprises me with its capacity to keep working. If anyone knows anything about this I would really like to hear it, I already checked out the wiring diagrams, but I obviously need to spend a little more time with them.
Right now, my best guess is one wire to the emergency flasher box, one wire to the front signals, one wire to the rear signals, and one wire to keep me guessing. Does the switch actuate the parking lights as well as the signals? I would have something to hook all my wires to then.
Come to think of it, I don't even know what flashers do. Is there anyone who has payed a little more attention to the things that have surrounded them their whole lives than I have who can tell me what lights come on when one hits the flashers? Do the brake lights still work, or do they get over ridden, what about the turn signals? Good God, I am suddenly completely clueless...
Thanks,
ALT

[FORDification]

The rear bulb is a dual-filament. When your headlights are one, one filament of the bulb is energized (the tail-light). When you hit the brakes, the second filament also lights up. When you turn on your flashers, you're simply energizing the second filament again...and again...and again, on both sides instead of just one side like the turn signal switch does. Stepping on the brake pedal while the flashers are engaged will simply overide the flasher, causing the filament to remain energized like normal brake lights. (That's because if you're driving down the highway with your flashers on, the folks behind you need to know when you hit the brakes.)

The flasher switch does also actuate the front signal lights in the same manner.

Read the following for a better explanation:
http://auto.howstuffworks.com/turn-signal1.htm
http://auto.howstuffworks.com/turn-signal2.htm

[Thunderfoot]

To add some more info with what Keith has.

The Emergency switch is actually in Parallel with the front turn signals and the brake lights.
Of the four connections;
1 goes to the emergency flasher (for the power to light the bulbs and make them flash),
1 goes to the Rear Brake lights (it is connected to the rear brake light wire in parallel before the turn signal switch),
1 goes to the Right front turn signal (it is connected in parallel with the right front turn wire),
1 goes to the Left front turn signal (it is connected in parallel with the left front turn wire).
The switch has to be normally open and the fronts have to be separate connections so that it doesn’t short out or affect the normal turn signal and brake light function.
That link Keith has above, has a good explanation of how the flasher works and turns to an extent. One thing I’d like to add is that the more current draw (more lights, like trailer lights added) makes it heat up faster and so they will blink faster. This is where the “Heavy Duty Flashers” are used as they can handle the extra current so they won’t do the fast flashing.
Also, one thing they didn’t cover in there on the Turn Signal Switch is that the Brake lights are also routed with the rear turn signals, and when you turn on the signal it disengages that sides brake light so that the brake don’t over ride it (like it does with the hazards on) This is also why when the Turn Signal Switch has a problem, that you can have the front turn signal work but not the back or vice-versa, the front and back lights are on separate circuits in a way.

Any other particulars on any of this or any other part of the lighting, let me know and I can help or explain better and modify some drawings if needed.

[Alfred Lord Tenniscourt]

That makes perfect sense. Thanks all. I let myself get confused because I did not think about being able to feed both the rear signals from the brake light switch, but having to feed the fronts individually so that it wouldn't cause both turn signals to come on every time you tried to use one or the other. That, and I kept thinking that if the brake lights and flasher worked at once, it would put 12v to each side of the bulb effectively turning it off. I know this makes no sense this morning, as the light fixture grounds through the body of the truck, but after a long day yesterday, I kept imagining the emergency flasher going to one end of the filament and the brake/turn signal going to the other...
I had to figure out the turn signals when I first got the truck. It was a mess. My truck is a 67, but it is titled as a 69, so I was looking at the wrong wiring diagrams. All the colors were wrong, some hack had the wiring harness full of bad connections and duct tape, and nothing seemed to make any sense, so I finally just decided to make something that would work... I ended up making a big truth table for all seven wires that came down from the switch. I wish I still had the thing, it was pretty cool looking and might actually help someone some day.
The long and the short of it is that I have been driving the truck for a little over a year now with a flasher box electrical taped to the steering column along with a huge ball of wiring that made the brake lights and rear turn signals work, but not the front signals or the indicator lights (because the truck is also noisy, I had to rest my hand on the flasher box to feel if it was ticking to know if my signals were on). I just put a new straight six in the old girl, and converted her to fuel injection with a megasquirt, so while I was wiring that up, I decided to re-wire the truck. It was sad to cut out the old wiring harness. Most of it was in really good shape, and did not need to be removed, but the element of uncertainty that had been introduced by some hack was too great, and I felt that it would be a better decision to verify that everything was nice and tight and right before I put her back on the road.
On a positive note, I get to change some things since I am messing with the truck myself, so I have installed two fuse blocks. One is hot all the time, and one is hot when the ignition is on. I have wished trucks came like that since I was a kid and put in my first radio. Now, when I want to add something, I just decide weather I want it on all the time, or only when the truck is running, and attach it to the appropriate fuse block, and install the appropriate fuse - no more trying to find a wire that I can splice into, no more crappy splice connections, no more wondering if the fuse that is in the block can support what it was originally intended to and whatever else I threw on the circuit.
I had a hard time finding fuse blocks like I wanted, but I found some at the marina. They have a power connection at one end, blade type fuse holders, screw terminals for each circuit, and nothing else... They are made to marine specs though so they cost me some money.
I am rambling.
Thanks again. I never would have gotten as far as I have if it wasn't for you'uns.

[Thunderfoot]

Sounds like you're have been having some fun on your project with the upgrades , and modernizing the wiring .