Have you checked/changed the engine temp sensor for the computer on the engine?,not the one for the dash gauge.
The temp sensor can really affect fuel mixture as does the map sensor(make sure it's getting good vacuum) and as do the oxygen sensors.
I can't look up your wiring diagram because I don't know model year?
On some makes and models, the lower brake lites are wired through the multifunction switch. Your turn and stop use the same bulb filament, just not at the same time. On a left turn, the left turn signal works, but the brake lite on the left doesn't. Now, the brake lamp on the right does work. The high mount brake lite also will work. The highmount brake lite is usually wired differently than the lower brake lites.
W/o being able to look at wiring diagram, I don't know if my info is applicable on your vehicle? I need model year.
You better read up on class 2 serial data communication networks . Does supply ACC voltage to anything . Your vehicle has many different control modules , PCM / ECM , air bag , ABS , BCM instrument cluster ,an the radio an some others . If you mess with or ground this wire your vehicle will not start or do anything .
The data link connector (DLC) allows a scan tool to communicate with the class 2 serial data line. The serial data line is the means by which the microprocessor-controlled modules in the vehicle communicate with each other. Once the scan tool is connected to the class 2 serial data line through the DLC, the scan tool can be used to monitor each module for diagnostic purposes and to check for diagnostic trouble codes (DTCs). Class 2 serial data is transmitted on a single wire at an average of 10.4 kbps. This value is an average; class 2 uses a variable pulse width modulation to carry data and depending on the message it may operate faster or slower. The bus will float at a nominal 7 volts during normal operation. Each module can pull this lower during the transmission. The bus is not at battery positive voltage or ground potential during normal operation. When the ignition switch is in RUN, each module communicating on the class 2 serial data line sends a state of health (SOH) message every 2 seconds to ensure that the module is operating properly. When a module stops communicating on the class 2 serial data line, for example, if the module loses power or ground, the SOH message it normally sends on the data line every 2 seconds disappears. Other modules on the class 2 serial data line, which expect to receive that SOH message, detect its absence; those modules in turn set an internal DTC associated with the loss of SOH of the non-communicating module. The DTC is unique to the module which is not communicating; for example, when the inflatable restraint sensing and diagnostic module (SDM) SOH message disappears, several modules set DTC U1088. Note that a loss of serial data DTC does not normally represent a failure of the module that set it.
On some vehicles, if the powertrain control module (PCM) is unable to communicate with the vehicle theft deterrent (VTD) system after the vehicle has started, the PCM will consider the VTD system to be malfunctioning. The PCM will enter a fail enable state and will command the security indicator to illuminate. When the PCM is in a fail enable state, the vehicle will NOT stall or stop running. If the PCM is in a fail enable state when the ignition is switched OFF, the PCM will remain fail enable until communications with the VTD system has been restored. When the PCM is in a fail enable state, the VTD system is NOT active and the vehicle will start. This feature is NOT available on all GM vehicle lines.
You need a interface module for your radio to work . Go to a professional installer place an talk with them . Your vehicle may not have all of these modules , but most .
Class 2 Serial Data Line
The class 2 serial data line on this vehicle is a star configuration. The following modules communicate on the class 2 serial data line:
• The body control module (BCM)
• The digital radio reciever
• The driver door module (DDM)
• The electronic brake control module (EBCM)
• The front passenger door module (FPDM)
• The HVAC control module
• The inflatable restraint sensing and diagnostic module (SDM)
• The instrument panel cluster (IPC)
• The memory seat module (MSM)
• The powertrain control module (PCM)
• The radio
• The radio amplifier
• The rear seat audio (RSA) controller
• The rear seat entertainment (RSE) assembly w/U42
• The rear wheel steering control module
• The remote playback device-CD player w/U1S
• The transfer case shift control module
• The transmission control module (TCM) w/Allison Transmission
• The theft deterrent control module
• The vehicle communication interface module (VCIM) w/UE1
GM Class II RDS Radio 12V Ignition Wiring
I couldn't find a self-help YouTube video specific to your vehicle, however I would recommend purchasing a service repair manual book or e-download specific to your vehicle; like Chilton, Motors, Haynes, etc., or calling your local Chevy dealership's service dept or parts dept and see if they'll tell you how.
