AlexLaumeyer

On my 73 delta 88, the left turn signal works very sluggish with the lights on but works fine if the lights are off, I tried cleaning the sockets and replacing the bulbs on the left side to no avail. I even replaced the turn signal switch in the steering column as well as the light switch. Any ideas what could be causing this issue?

joe_padavano

You have a bad ground on the left side that has high resistance. With the lights off, the turn signal circuit is able to ground through the light circuit due to the common ground in the 1157 bulbs. With the lights on, you have 12V on that circuit and the ground is forced through the high resistance, which is why it flashes slowly. I'll bet that with the turn signals off, the parking or tail light on that side is dimmer than on the right.

AlexLaumeyer

I’ll see what I can find but I bet that you’re right. Won’t get to it until this weekend.

rocketraider

These cars have a dedicated ground wire from parklamp socket to chassis ground. The header panel is fiberglass and the 5mph bumpers are mounted to shock absorbers. Neither provides a ground path, hence the separate ground wire.

Find the socket's black ground wire and follow it to where it attaches to the radiator support, usually behind the headlight area. Check that ground wire for continuity from the metal bulb sleeve in the socket to the ground point using a self-powered test light. Wherever it doesn't light is where the fault is.

These sockets weren't especially reliable new and nearly 50 years age doesn't help them. Replacements are available.

If you don't have it, strongly suggest getting an original printed copy of the 1973 Oldsmobile factory Chassis Service Manual. It has color wiring diagrams among other things.