Turn signal lights acting weird

[hatzie]

The 168 peanut bulb front side marker lamps do not have a ground on the same leg all the time so you cannot use LED bulbs in those sockets or the 1157A bulbs in the front turn/parking lamp sockets.
How did GM light the bulbs without a ground? GM ran the front side marker lamps from the parking lamp HOT to the Turn signal HOT wires.

This means the 168 peanut bulb side marker lamps on the squarebodies ground through the tungsten turn or parking lamp filament of the 1157A bulbs in the front turn/parking lamp housing. There are a bunch of vehicles made from the 1930's through the 1990's that did this.

When the parking lamps are switched on, the side marker lamps receive a ground through the turn signal filament when the turn signal is off so they shut off when the turn signal is powered on. This makes them light up when the turn signals are off. Kind of a wig-wag on the front corners at night.

When the parking lamps are switched off, the side markers ground through the parking lamp filament when the turn signal on that corner is hot so they light at the same time as the turn signals.

If you use LED bulbs in the front marker lamps and/or your front turn/parking lamps you'll likely get strange behavior from your front turn and parking lamps.