2002 Chevy Astro Van turn signal?

I bought a 2002 Chevy Astro Van AWD as a totaled insurance wreck. I am almost done with it but have one electrical problem.
I have no understanding of the "theory of operation" of the turn-signals. I have a full set of Chevy tech manuals for 1996 Astro Vans but for 1996 it is obviously different. So at the moment - I do not have a good idea on how this was supposed to work when all is right.

When I turn on the right turn signal - there are two separate bulbs that flash consecutively. I.e. first one, then the other, then back to the first, etc. NOT both at once. There is the main big bulb that blinks "on", and then the smaller marker bulb blinks "on." The problem is with the left (driver's side). For that side, only the big bulb blinks and does it twice as fast as is supposed to. Nothing from the smaller bulb. Note also that the same smaller bulb is a parking light when the flashers are not used. When I put on the parking lights - all work except the front left. I have no wiring diagram for a 2002 and don't know where to start. I am wondering - what actually does the flashing? If it is the flasher unit - I am wondering how it makes two bulbs flash independently at different times?

I could just say the heck with it and stick in an electronic flasher unit that is not load-dependent. That won't fix the actual problem, but will let the larger flasher bulb blink normally.

Could it be as simple as a faulty bulb?

Fast blinker usually means one bulb is burned out. Maybe go over the grounds for the other side, I thought they always flashed together.

I would guess you have a high resistance to ground in one or more assemblies.

(quoted from post at 10:57:58 12/11/17) I would guess you have a high resistance to ground in one or more assemblies.

Click to expand...

I agree , probably the supply to lamps works but there is a a high resistance path back to to chassis .

The alternating flash is caused by a bad ground.

Could be in the socket or where the socket grounds to the chassis. Usually a black wire, will terminate close by with sheet metal screw.

The rapid flash is a built in warning that one of the lamps is not working. It could be a bad lamp, loose lamp/bad socket, or a faulty ground.

My first area to trouble shoot would be at or near the actual lamp that is not working. Does not sound like a wiring or switch problem.

I agree it could be a grounding problem. I once had an Olds 88 that began doing all manner of bizarre things, like the cruise control disconnecting when the left turn signal was activated, etc. Turned out to be a loose ground wire hidden inside the left fender. And they do put ground wires in sneaky places.

But, if it were me, I'd start by checking the bulb, or bulbs, and sockets.

Fast blinking is a bad bulb. It might, still have a can that controls the blinking. Though usually that gives no blinking at all. A 15 year old vehicle, with a pretty complex electrical system that has been wrecked could be a challenge!

Without going into detail, the small bulb grounds through the 2nd element of the larger bulb. All those bulbs ground at the same point near the LH headlamp but the little marker lamp bulb feeds ground through the bigger bulb

Thanks for the replies. All the bulbs are new and fine, front and back. I tested each one. I still have no idea what is going on. One added thing I noticed. When I turn on the ignition and turn on the parking lights - the left-hand turn indicator is on, in the dashboard (steady). When I put the turn signal lever in "left turn", that indicator blinks but super fast. As I said before, each side in front has two bulb. One is a large dual-filament bulb and the other one of those tiny 194 bulbs. That tiny 194 bulb never lights up.

I will note that the windshield wipers and washer in front did not work at all. Ended up that was caused by a bad ground. Wiper-motor has a metal ground strap and it was making bad contact. So I guess it is possible there is another bad ground somewhere. I wish I had a wiring diagram.

The entire front-cradle that holds the radiator, condenser, etc. was destroyed in the crash and it is not a bolt-in part. I had to cut it out and weld-in a new one. When I did that, I cleaned all the ground points on it (there were four of them).

When I bought this thing - I did so because it is an usually clean van for the year. I wrongly assumed at the time that the front cradle was a bolt-in part. Boy, was I wrong. I is quite a job to replace. Plus I had to get one which meant half a day at a junkyard finding a good one and then cutting it out. Still - I paid $700 for the van and $200 for all the parts at the junkyard. That included front cradle, hood, grille, headlight assemblies, grille, fan shroud, etc. Another $200 for new oil-cooler lines and a new radiator. It runs like new so I guess I did okay. This light is the last thing I have found that is not working properly. Not sure I ever want to do another one of these though.

(quoted from post at 14:23:18 12/11/17) . When I turn on the ignition and turn on the parking lights - the left-hand turn indicator is on, in the dashboard (steady).

Click to expand...

My 1984 K20 plow truck did the same thing. Turned out to be a broken ground wire in the parking light that is part of the plow lights.

This is a picture of a confused ground. The blinker is trying to light three lights. This causes the flasher to blink quickly

As others have suggested it is the ground to one of the main turn signal bulbs may even be a poor
connection to the bulb in its socket. How it blinks the bulbs in an alternate sequence is easy to
explain, well kind of. Okay first I will say my explanation applies to a front turn and marker on a 79
Chevy pickup. I?m not sure if your van is wired like this or not. Also at some point I think GM went
with the wiring trend to have a separate circuit to both the tail lights and rear turn and brakes,
which only effects the tail lights. So hear goes; in the case of the pickup the marker bulb has
neither lead connected to a ground. One side connects to the + side of the turn signal and the
other to the + side of the tail lights. So when the lights are off that side of the marker bulb is
grounded through filaments of the tail light bulbs so the marker bulb blinks simultaneously to the
turn signal. When the tail lights are on then the markers will blink alternate of the turn signal
because the tail light side is powered and the turn signal then provides the ground through the
bulb filament during the off segment of the blink. The filaments in the markers are smaller (more
resistance I think is the proper term) so they light instead of the larger filament signal bulbs. Best
explanation I can give. Clear as mud?? Lol!