Brake Warning Light - False Illumination
Bulletin No. T 84-39 File In Group 5Number 9
Date Jan. '84
SUBJECT: BRAKE WARNING LIGHT CONDITIONS
MODELS AFFECTED: 1984 ELDORADO AND SEVILLE WITH HT4100 GASOLINE ENGINES
FIGURE 1 - Vacuum Port - Plugged:
FIGURE 2 - Vacuum Port - Open:
Incorrect Brake Warning Light Switches
Some early production, 1984 Eldorados and Sevilles may falsely indicate a low vacuum condition as a result of brake light illumination during hard or repeated brake pedal application. This may be caused by the incorrect usage of 1983 low vacuum switches on 1984 vehicles. The 1984 switches can be distinguished from the 1983 switches by looking directly at that part of the switch which sits inside the vacuum chamber of the brake booster. The 1984 switch, Figure 1, will have a silver center plug as compared to the 1983 switch which has an open port, Figure 2. If a 1983 switch is on a 1984 vehicle, replace it with GMWDD P/N 18010278.
To aid in the removal of the low vacuum switch, make sure the vacuum reserve is exhausted from the vacuum booster by repeatedly depressing the brake pedal until a stiff, hard pedal is felt. Caution should be exercised during removal and installation to prevent damage to the grommet. Lightly apply silicone-lubricant on the switch to aid in installation.
For warranty purposes, use Labor Operation H0770 at .2 hour.
It is important to note that repeatedly applying the brakes in a fast manner while the engine is at idle may cause an illumination of the brake warning light between the fourth and sixth pedal apply. This does not indicate a system malfunction and should be considered normal.
Incorrect 1984 Wiring Circuit Diagram
The brake light vacuum module, shown in the 1984 Seville and Eldorado (DFI) Chassis and Body Electrical and 1984 Deville and Fleetwood Brougham (DFI) Chassis and Body Electrical wiring circuit diagrams, is incorrect since they are not used on the 1984 vehicles. The correct 1984 Seville, Eldorado, 1984 Deville and Fleetwood (DFI) electrical wiring circuit diagrams are shown in the Electrical Section, Section 8, of the 1984 Service Information Manual. Make the changes on your copy of the Chassis and Body electrical wiring circuit diagrams (bedsheet) for future reference.