I have an 86 cutlass runs great, however I'm having some electrical problems. The tail lights won't come on and if they do they won't turn off. I've replaced the alternator and the b

Start with your fuses under the dashboard by the driver's shin bone. Remember that fuses can be burned out and not show it.
Take a test light or meter and check the contacts on each end where the fuses go, with the key on, and the lights on, to be sure there is electricity getting to the fuse.
After that, check each light bulb in the rear of the car.
Remember, the bulb can be burned out and not show.
Also check your clearance lights on the rear.
Take a test light or instrument and check all the sockets to be certain the electricity is getting to the socket when the lights are on and when the brake pedal is pressed.
God bless your efforts.

pull your brake light assmb out and check your connections including ground

Those are all really common symptoms of the alternator going bad on those cars. I would have it checked to make sure it's charging properly.

usualy there is a faulty earth to the bulb cluster remove them and clean all the conectors spray the harness and cluster with wd40 or similer put all bulbs back in and see if that works but i would go with a bad earth hope this helps ivan uk

Batter charged? Could be a starter also. And dirty cables. Does the interior lights work or head lights.

I assume you checked the bulbs and they were good? It's possible that the sockets have gone bad and need replacing. The tail lights are fused through the instrument panel lights. that fuse should be in the middle of your fuse box, marked "instr". If the fuse is good check to see if the dash lights come on when you turn the headlight switch on. If they don't then change the headlight switch. hope this helps.

Maybe try to run new wiring or check for worn insulation in wiring from front of vehicle to tail lights. Maybe try to take it to an 'auto electric' shop for this service, where they can check the wiring for shorts to ground. This can be expensive, but sometimes it's best left to the experts to avoid costly mistakes.

I've got the same problem on 98 GMC Sierra.

I'm an electrical engineer, I checked the electrical diagrams and verified that there is no problem in the rear lamp assembly or wiring. With the light assembly unplugged, I can actually watch the blinker and brake signals operate with a voltmeter. The Tail light works OK.

It simply won't provide enough current to light the bulbs.

I'm afraid that it's melted one of a pair of normally closed contacts inside the blinker switch that feed the brake and turn separately on each side.

first eliminate the possibility that you have the wrong bulb in the wrong socket. it sounds dumb but going way back to 1157 bulbs there have been two rear tail light bulbs which will fit into the same socket but are electrically different. If you have ever driven down the road following a car which had one bright and one dim tail light, or brake light, then you have seen this in action.

since you have one good tail light assembly remove the bulbs, taking great care not to mix them up and make sure the bulbs are exactly same as in the non working assembly. i mean you have to look closely at the bulb's connection points as they will look very much the same.

if the bulbs are correct then you are looking at buying a new socket, or light assembly if the whole thing is wired into the car.

First Look For A Bab GROUND Usually in the TRUNK in or Close to the Junction PLUG Normally on the LEFT Side of Trunk. Sense you DO HAVE All other Lights In Rear, its A Remote Idea that Ground IS the Problem. BUT A GOOD Rule in AUTO ELECTRICAL is to RULE OUT GROUND. ALSO License Plate Lights are On SAME CIRCUIT So IF they DO NOT Work then
The HEADLIGHT SWITCH is The Problem Because The "TAIL" Lights are Separated From Headlights in the HEADLIGHT SWITCH, To TEST with a TEST-LIGHT you Will Be Looking for the BROWN or GREEN Wire Coming OUT of the Switch. I Hope This is the Cure for Your Oldsmobile. I Feel Confident that this WILL Help you to Get your TAILLIGHT'S WORKING. Have A Great Day ! , rejakwilson