1999 corolla high beam light flicker

Could be the battery. Jump it with another car and see if it stops. Ford put the security in the Instrument panel for a few years. This flickering could be the reason in shuts down after a couple seconds.

Replace the turn signal switch. all exterior lights run threw it.

Normally when headlight flash its and overcharge problem max volt from the alt is 14.5 video is if you got to change your alternato

if you did it yourself and did not use factory lights or ballast then it could be a voltage detection problem. If you did use factory parts then the headlight switch may have failed by coincidence. also check connections at HL plugs and or switch. ???????????

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replace the serpentine belt and adjust it properly

Sounds like you may have a faulty headlight switch.

the drl relay could cause the lights to flicker and possibly no high beams as the drl uses the high beam filament.also it could be the dimmer switch located at the base of the steering colume were the dimmer switch rod works the switch.

Not knowing the year make or model car i can only guess here, but it sounds like the switch may be bad, try unconnecting the connector from the switch and see if the tail lights shut off, the flickering high beam indicator may be due from a faulty switch or high beam relay but if all works manualy i dont think its the relay.

It is caused usually when the arternator is going bad

First place to start is with headlight switch. I did have a case many years ago when both high beams were blown out at once, but this is rare. When you have the headlight switch out, jump power from te low beams to the high beam contacts. If high beams come on, replace switch.
Bill