Right-front turn-signal light won't flash with headlines on

[82ChevyC10b]

I have a 1982 Chevy C10. I replaced a blown front-right (passenger-side) amber turn-signal/marker bulb today, using a 1157NA as the replacement bulb. (The bad one was a 2057NA.) Later on, while checking all of my lights, I noticed that with the right turn signal on and the headlights on, the replacement bulb burned brightly (both filaments) but didn't flash. When I turned the headlights off, the signal bulb flashed like it's supposed to. Everything is OK with the signals in the back and on the front left. Could the problem here be a bad ground? Thanks.

[bd]

Could the problem here be a bad ground?

This ^^^^^.

Make sure that the lamp ground connections to the radiator support are clean and tight and that the radiator support has a good 12-gauge or larger ground wire connected to the battery negative post.

[82ChevyC10b]

Thanks. I'll check on the ground connections.

[frotosride]

That ground if it's still in factory condition will be on the inside of the core support, between the radiator and battery. Should be a 1/2" with a star washer on it. Check the wire as well to make sure it doesn't have any breaks in it.
Using a voltmeter will likely lead you down the wrong path with this test because a simple resistance test to verify continuity only needs one strand of wire for the voltmeter to give you a good reading. It will not show resistance under load and the load is what the flasher needs to signal the build on and off.
Recommend verifying the ground is still connected, turn headlights and blinker on and, inch by inch, bending the wire back and forth to see if the blinker comes on while inspecting for Knicks in the insulation. It's a short ground wire so it won't take long.

A ground is most likely but there are still other possibilities but to avoid running down to many roads at once, run this one to ground first! Hope it's this simple.

[82ChevyC10b]

Happy New Year, everyone. OK, so I checked the ground from the bulb harness, and it appears to be good. That's not the issue here. What else can I check, or do I just go ahead and replace the turn signal bulb harness (socket) with a new one? Again, the turn signal on the front right works until the headlights are turned on, and then both filaments in the bulb light up -- with no blinking. The side marker light on that side works just fine in signal mode with the headlights on or off. Thanks.

[frotosride]

Are you sure you have the right style bulb?
Secondly, the tall filament is the market light (low/dim), the shorter filament is the blinker(high/bright). what it sounds like is either the bulb is the wrong type, pins on the bulb are misaligned, or the socket is broke and causing misalignment. The reason I say this is the bright filament shouldn't be on with the headlights at all and unless you have disconnected the wires and ran them in a different configuration, only the marker filament should light.
The high/blinker(short) filament receives power from a different source than the headlights, the marker lights do not.

Check the socket and the bulb it's self. You should be using a 2357 style bulb which has a high pin and a low pin protruding from the metal body(ground contact). You used the wrong style or put in in wrong and twisted the bulb too far causing both filaments to receive power when the market lights are on...
It is hard to see that there is a low and high receiving portion of the socket and the older the socket the easier it is to force the bulb in the wrong way. If you look into the socket you will see two metal plates separated from each other. Here is where each filament receives power from. Turn the market lights on and then reinstall the bulb. Make sure that only the dim filament is on. If it is not then rotate the bulb 180* and put it back in. *If you leave the bright filament on as a marker light it will shorten the life span of the bulb and melt the signal housing... Enjoy and keep plugging away.

[82ChevyC10b]

I'm pretty sure the OEM bulb on this truck for each of the front turn signals is an amber 1157, which is what I'm using on the front right. I'm wondering now if the issue might have to do simply with mismatched signal bulbs on the front left and right. I have an older (and dimmer) 2057NA bulb on the front left and a new 1157NA on the front right. I have some more amber 1157s on mail order. After they're delivered, I'll match up the bulbs on the left and right and see what happens.

[82ChevyC10b]

The problem is fixed, and the solution turned out to be simple. I simply replaced the 1157NA signal bulbs on both sides in the front with matching new bulbs. Now, the turn signals blink on both sides with the headlights on or off.