Headlights and taillights were flickering

The mechanic is now using a Duralast alternator pigtail (part number 237) to connect with the new Carquest alternator. The old gm pigtail alternator connector was crack (fell apart) when checking it. We are wondering if a gm AC Delco pigtail connector is needed. The battery is putting out about 11.8 volts and the alternator 13.66 volts standing outside the car. However, my instrument cluster is displaying 10.8 volts (idle about 30 minutes) even though we check the battery and alternator outside the car with a multi-meter and his $1,200.00. Harbor Freight Zurich Pro. We let the car idle about thirty minutes. As I sat in the car the lights and dash start flickering like a few days ago. Help.

Time is about 7:50 pm eastern standard time 4 July 2019. The alternator was replaced two days ago with a new Carquest alternator. The same alternator which has been in the car for six years. After letting the car idle for 30 minutes today. I then drove for five miles. While idling again the lights started to flash along with the digital instrument cluster. The headlights will not flash if the light switch is pulled out in manual *(on) mode. The battery today reads 11.84 volts with engine off. With engine running the alternator puts out 13.45 volts. The battery output on the digital instrument panel is showing 10.8 volts. This reading normally shows 13.8 volts. The alternator pigtail broke into pieces. It was replaced with an AutoZone Duralast 237 connector. Only two wires of the connector is being used from the pigtail. The codes picked up were p0603 control module long term memory reset. Code 2 (ipc) b1983 battery source volts low. Zurich zr pro scanner used to test the car health. Help

7 July 2019. The car now has another new Car Quest alternator. This alternator was bench tested as good. I did not have the first alternator benched test. The car now has a new Duralast battery. The digital instrument cluster now shows 11.8 volts (new battery) instead of 10.8 volts before I changed the battery. AutoZone charger stated the battery had a dead cell. Both battery cable (side posts) were changed. All grounds have been cleaned. The pigtail is still Duralast. We cannot find out where we are loosing volts. The car was again driven for two miles with the same results. Flickering interior lights, flickering head lights and tail lights, flickering dome light, A/C goes on and off. Any suggestions?

Let me tell everyone when I recognize I had a problem.

I purchase new AC Delco shocks and a new AC Delco air compressor for the shocks. There was no suspension problem light, but the car would sag with a load in the rear. When I went to pick up the car from the shop there was a mechanic in my trunk (feet first) looking for the relay that goes to the shock. I watched him from the bay doro as we talked about him being the smallest mechanic in the shop. I had also ordered a new relay because I wanted to have no more problems "for a while" with the air ride. I purchased the car in 2003. The prior owner purchased the car in 1998. The mechanic changed relay after relay until he found and switch the correct relay. I took the car home twenty minutes later. My wife and two grand kids immediately came out the house and got into the car. We immediately went back to the shop to show the mechanics how well the car was handling the load. You could definitely feel the difference with the new air ride. I stop to put gas in the car about 15 minutes later. I always reset my mileage indicator. My gas tank has never been less than a half of tank of gas. When resetting the mileage, I notice the voltage at about 9.7 volts. Now I watching the voltage reading as I took my wife places she wanted go in our small city. About 60 minutes riding around town I notice my digital display in my cluster fluctuating between 9.7 volts and 8.9 volts as I was driving around the city. For about 30 seconds it jumped to 10 volts. We went to AutoZone before going home. The AutoZone employee told us the alternator voltage was fluctuating up and down. He suggested I replaced the alternator because the battery was good. Now everyone knows how this adventure started. However, the flickering (dash, interior and exterior lights, radio) never occurred where we were out. Now it occurs after about 20 minutes of driving. We have been wondering could anything have occurred in the fuse box in the trunk. We have checked fuses and relays back there. Thanks again.

Thanks. I will get back to as soon as possible.

12 July 2019. 10:31 PM. We got a chance today to follow-up on the help provided in this forum. The car started up perfectly again today at about 3:00 PM eastern standard time. The engine is quiet and smooth. The voltage still reads 10.8 volts on the digital instrument cluster (DIC) after sitting overnight. In fact the voltage always return to 10.8 from sitting overnight. I discover today that the voltage on the (DIC) went from 10.8 to 9.9 volts when I went manual with the headlights. I turned the car off for about two minutes. The voltage on the DIC returned to 10.2 volts when I started the car again. The voltage on the (DIC) went from 10.2 to 9.9 volts when I went manual with the headlights AGAIN. I did start the car for about five minutes. The voltage on the DIC returned to 10.3 volts when I turned the car on. The highest the voltage returned to on the DIC is 10.6 again going through the cycle again and again with longer wait periods. I stopped after an hour of this because I had to run some errands with my grandson. By the way, I also used a new headlight switch (GM) today and got the same results. Someone on eBay had one for a hundred dollars that I had been watching for a few weeks along with other parts. I decided to purchase it a few days ago. I did not take a test drive to see if the DIC would flicker or the radio volume go in and out. Once again thanks for your help.

I took the car to my favorite shop. Once I explained that when I pulled out the headlight switch that the digital dash would go on and off. The voltages would drove to about 8 volts on the dash when you could read it. The radio would go on and off. The AC would go on and off. The digital dash was reading 10.2 volts. He checked the gang plug which is on the driver side by the strut tower. It has three prongs. Two of the three were reading about 13.8 volts. The third was very corroded and reading 8.6 volts. He cleaned the corrosion from the prong reading 8.6 volts and the entire gang plug. The digital dash now reads 14.2 volts when I start up the car.

Thanks for all your help.

I took the car to my favorite shop. Once I explained that when I pulled out the headlight switch knob (turned on the headlights) the digital dash (instrumental cluster) would flash on and off until it would go completely blank (10 to 15 seconds). The voltage would drop to about 8 volts on the dash when you could see it. The radio would go on and off. The AC would go on and off. The digital dash was reading 10.2 volts after starting the car. He checked the gang plug which is on the driver side by the strut tower. It has three prongs. Two of the three were reading about 13.8 volts. The third prong was very corroded and reading 8.6 volts. He cleaned the corrosion from the prong reading 8.6 volts and the entire gang plug. The digital dash now reads 14.2 volts when I start up the car.
Thanks for all your help.