Brake warning light

1992 GMC SIERRA
140,000 MILES • 5.7L • V8 • 2WD • AUTOMATIC
Avatar
RIESLING
  • MEMBER
  • 3 POSTS
I had the brakes serviced and soon after the brake warning light started coming on intermittently. Recently the light has been coming on regularly. As a test the sensor wires from the parking brake and proportioning valves were disconnected but the light still came on. Furthermore, I've notice the light comes on only once the speed reaches 35 mph. Any ideas how to correct this problem would be appreciated.
Aug 27, 2020 at 9:12 AM
Advertisement
Avatar
ASEMASTER6371
  • CERTIFIED EXPERT
  • 52,796 POSTS
Good afternoon,

Is this the yellow brake light or the red light?

The red light comes on with the proportioning valve, e brake switch and the float in the master cylinder if it has one.

Can you verify?

Roy
Aug 27, 2020 at 11:05 AM
Avatar
RIESLING
  • MEMBER
  • 3 POSTS
Thanks for the quick response. This is a red brake warning light. It covers the items you mentioned except there isn't a level sensor on the master cylinder. As an added note, if the e brake is pressed when the warning light is on the light becomes brighter.
Aug 27, 2020 at 12:25 PM
Advertisement
Avatar
ASEMASTER6371
  • CERTIFIED EXPERT
  • 52,796 POSTS
Okay, I attached a wiring diagram for you to view. In the diagram there is a diode in between the cluster and the switch in the e brake. See if you can find this diode. It is most likely wrapped around the harness under the dash.

Roy
Image (Click to enlarge)
Attached Media
Aug 27, 2020 at 1:08 PM
Avatar
RIESLING
  • MEMBER
  • 3 POSTS
Thanks. I'll check the wiring. Still baffles me why light will go on at a certain speed.
Aug 27, 2020 at 4:40 PM
Avatar
ASEMASTER6371
  • CERTIFIED EXPERT
  • 52,796 POSTS
Most likely due to the charging system voltage.

Roy
Aug 27, 2020 at 4:41 PM