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Electrical problem in 1999 Prism

We bought this Prizm with a salvage title. One part that had to be repaired was the turn signal switch on the right side of the steering column. Now, we’re having a number of electrical problems. When we turn on the headlights, the car dies. When we use the turn signals, the car dies. Before the turn signals caused the car to die, the emergency brake indicator on the dashboard would flash at the same time as the turn signal indicator. The tail lights would be on all by themselves, and when we turned on the accessories, there would be a buzzing sound from under the dashboard. We would appreciate any suggestions. We’ve already stumped one repair shop, and the fellow who did the original salvage work has had it two days with no success. Appreciate whatever you can do to advise us.

This may be a straw to grasp onto but you may have a loose ground somewhere. I take it that the car was in an accident, it having a salvage title? A connection may have broken or jossled loose.

The engine needs a decent ground to run and it may be missing. Instead, it may find its way back to the battery by some accessory connection somewhere. That connection is likely much thinner than the engine normally needs.
Turning any of the accessories on causes more current to flow through that connection, starving signals going to and from the engine. Sending current through a thin ground connection could actually lift ground higher than it should be - it is called ‘ground bounce’. It can really hose electrical systems up badly, causing all sorts of weird intermittent problems that may seem impossible to debug.
That’s why you often have more than one ground connection from the frame to the engine, one to the transmission, one to the dashboard, etc. Ground is usually a star connection, never in series, for that reason.

The following won’t cost anything and is worth trying:
Get a booster cable. Use only the negative connection - let the positive dangle. Don’t use the positive at all because that’s potentially quite dangerous.
Clamp the negative side of the booster cable onto the negative battery terminal and tie the other side to the various pieces of steel you find (engine, frame, dashboard brackets, etc).
See if it makes a difference.