98 blazer headlights flicker and brake lights out

[stuandray]

At night with the lights fluctuate in synch with what sounds like the fuel pump ( a noise from the rear). The faster I drive the less it is noticable. If I am idle or in park the fluctuation is bad the dome dash and radio lights all flicker. Also my brakes lights just went out altogether all fuses and bulbs are good I already replaced the brake pedal switch and all the other lights work fine (park, turn, reverse). Any one familair at all with these problems. Ps onyone no a good method for changing the spark plugs and wires out?

[Gabe25]

Try taking a look at your alternator and see what the voltage out put is. With the motor at idle, it should be around 13.5 volts. If not, possible faulty alternator.

[Brian_D]

The brake lights run thru the $365.71 Multi-function switch (turn signal switch)! Take a look in the back of the Chilton book for brake light wiring diagram.
I recently had to replace the turn signal switch on my '97 due to no brake lights - hazards, turn signals, headlights, wipers, cruise - all worked fine.
Eliminated the Brake Switch and the BTSI (Brake Transmission Shift Interlock) solenoid: could shift from PARK with the brake depressed.
Eliminated the Park-Lock solenoid: could remove key from ignition.
I'm keeping to defective unit to disassemble to determine point/cause of failure.

After a little more thought, I would start by disconnecting the battery, then unbolting the ignition/multi-function wiring harness under the dash, and using some good electrical contact cleaner - clean both sides of the wiring harness. Allow ample time to dry before reassembling and reconnecting the battery.