Both turn signal indicator lights and the high beam light illuminate on my 1984 corvette from time to time and when they do the digital dash dims. Sometimes it goes away on its own and other times it takes turning off the ignition and locking and unlocking the doors to get them back to normal. I think it is related to the security system because at times the security system will set off the horn even after I unlock the doors with the key.
in an almost 30 year old car... you have started to have bad ground connections...but i should explain about the automotive word GROUND.. in a car.. the GROUND side is HALF the circuit.. the electrons also flow from Negative/Ground to the positive side.. if you loose a ground.. you will not have enough electrons to make the circuit work.. but electrons will try to come through other circuits.. the LONG way through.. this is why.. your turn signal and high beam indicator lights are coming on when you have an issue with a different ground connection.. to find a bad ground is usually NOT hard... you will need a hand held digital volt meter.. they cost between 7 and 25 bucks.. you will want to print this and follow it step by step.. this is the FIRST STEP in finding the bad grounds near the engine and battery.. those have to work perfectly.. or any other testing is worthless... and its really simple.. engine running .. turn on the headlights... hood is open of course..digital volt meter set to 20 volts DC scale.. 1. measure between the Negative battery post and the positive battery post.. 14.1 to 14.8 is expected.. 2. measure between the Negative battery post and the Engine ... 0.04 volts is expected..3. measure between the Negative battery post and the BODY/Chassis . 0.02 volts is expected4. measure between the Engine and the BODY ... 0.02 volts is expected...if you get 0.00 on the last 3 test.. reset the meter to 2 volts DC scale.. and retest 2, 3, 4.. if you get more than the 0.04 or 0.02 volts on the last 3 tests.. you have isolated the bad ground connection .. this test only works with the engine running and the headlights on..if you get 0.00 with the meter at 2 volts scale.. the test is being done wrong.. takes just a few minutes...but again.. its the first part of the trouble shooting...please post your results..
this question comes up a LOT about GROUND locations.. so i spent some time last night .. did some digital editing.you will probably want to print this..
pay close attention to connections at 14 and 20, and on the side of the block at bolt 18 connection 22 just above the oil filter...back of the head #11 bell housing bolt #12... these last 2 shown in the upper image..if you get 0.04 or 0.02 on the 4 part test above.. then the grounds under the hood are probably good.. and your ground issue is probably under the dashboard...why is such a small voltage good and 0.00 bad..copper wire has resistance in it.. when the current is flowing between parts along the wire there will be less voltage at the load end... this is what you are measuring... the voltage drop... engineers use this system to select and verify the proper size of wire .. too thin a wire will have excess voltage drop.. causing the wire to get hot or the part to not receive enough voltage to properly operate.. too thick a wire for the load is a waste of very expensive copper wire...just think of how much wire is in each car.. if you think this is a lot of ground connections.. look under the hood of a mid 90s toyota... there are 6 ground wires between the engine and the body and battery negative.. all going to slightly different parts.. but all on the same motor.. i took a an hour last month and cleaned them on a friends camry.. brought his charging voltage up from 14.1 to a rock stable 14.6.. and cured all kinds of issues on how the car ran.. ended the stalling issue.. the headlights were brighter also... with the negative electrons coming from the alternator to go into the negative battery.. when the ground connections were not proper.. there was too much voltage on the engine block... and it was not getting to the battery or the body properly...another friend had a 98 chevy truck with issues.. test 4 had 8.5 volts between the engine block and the body.. that was a TOTALLY different truck when i fixed the dirty ground connection at the front of the block.. i had already fixed the negative connection between the battery and the body... somebody had just twisted it and taped it..