98 chevy blazer turn signal relay buzzes except when signal on

The universal harness with four wires assumes that the brake lights and turn signals use the same bulbs. If your Blazer has separate bulbs for rear turn signals and brake lights, this 'universal' harness will not work unless you buy a separate adapter to merge the power to the brake lamps and turn signals for the trailer.

you might want to check the bulbs they could both be bad

Start by looking closely at the filiments in the tail light bulbs. check for porper grounds.

Check the light switch relay mounted on the steering column under the dash right above the brake peddle.

Sounds like your brake light switch, located on the brake pedal, has gone out. Shouldn't cost to much at auto parts store. Thanks for using fixya.

Replace the hazard warning light switch. Pretty common problem on GM vehicles

Combination switch in the steering column is most likely bad

try working you hazard light switch a few times this will cause the turn signals to lose contact. it is a common problem

Unplug the turn signal relay from the fuse box and start you engine. Does it still make that noise?
If yes... Put the relay back in, that is not the problem.
If No...Then the relay could be bad, replace it!

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The Turn signal relay on a 94 s10 blazer is located under the cluster area right behind the panel that holds the parking brake release handle you will see it once a couple of trim panels get remove it will be to the right side of the brake release handle