Changed out the front brakes & the brake fluid sensor cap on my 85 jag, i press on the brake pedal but the brake lights wont go on.

Make sure if you have a fluid lvl sensor on the master cylinder, that it is plugged in. Also, if the old master cylinder had a lvl sensor, make sure your new one is equipped with one. If you do not have a lvl sensor, then it would be a pressure switch. Make sure it is plugged in properly. Does the vehicle have good firm brake pedal when it is running and the booster is assisting? If not, then you probably still have air in the system somewhere. Remember when bleeding brakes, start with the furthest wheel from the master cylinder and work your way to the closest.....Right rear, Left rear, Right front, Left front in most cases.

Sounds like a master cylinder, make sure you bench bleed the new one before installing

Section 06-06: Hydraulic Brake System 1992 Festiva Workshop Manual GENERAL SERVICE OPERATIONS Manual Bleeding

1. Read Hydraulic System Bleeding General Information.

1. Clean all dirt from the master cylinder filler cap.

1. Fill the master cylinder with the specified brake fluid. During the bleeding operation do not allow the master cylinder to run dry.
   

1. If the master cylinder is known or suspected to contain air it must be bled before the wheel cylinders or calipers. To bleed the master cylinder, loosen the front line fitting and have an assistant push the brake pedal slowly through its full travel. While the assistant holds the pedal, tighten the brake line fitting. After the line fitting is tightened, the assistant may release the brake pedal. Repeat this procedure on the rear brake line. Repeat the entire process several times to ensure all air has been removed from the master cylinder.
   

1. Remove the bleeder screw cap from the appropriate rear wheel cylinder.

1. Position a box end wrench on the bleeder fitting.

1. Attach a rubber hose to the bleeder fitting. The hose has to fit snugly around the bleeder fitting.
   

1. Submerge the free end of the hose in a container partially filled with brake fluid.

1. Loosen the bleeder fitting approximately three quarters of a turn.

1. Have an assistant push the brake pedal slowly through its full travel and hold it there.

1. Close the bleeder fitting.

1. Have the assistant release the brake pedal.

1. Repeat Steps 9 through 12 until air bubbles cease to appear at the submerged end of the bleeder hose.

1. When the fluid entering the bottle is completely free of bubbles, tighten the bleeder screw, remove the bleeder hose, and install the bleeder screw cap.

1. Repeat Steps 5 through 14 at the appropriate diagonal front caliper.

1. Check the master cylinder fluid level. If necessary fill it to the correct level with the specified brake fluid.
   

1. Check pedal feel. If the pedal remains spongy, repeat the bleeding process or, if necessary, refer to Diagnosis and Testing in Section 06-00.

By the brake pedal is a brake light switch. replace that item

Check your brake fluid level in the reservoir; some Toyotas have wheel cylinder sensors; some Toyotas have master cylinder sensors; you also have a sensor on the parking brake and on the brake pedal inside the cab. Check all that.

You also have to bleed the ABS system

For front brake pads replacement you need only usually wrench set, inclusive 7 mm allen key also. But for rear brake pads replacement you need obligatory a special caliper piston pressing tool, in order to press back rear caliper piston with parking brake automatic adjustment!!! For front brake pads. First you must verify yours front brake disc diameter: 280 mm or 288 mm. (On my car y have 288 mm). After that you can buy the brake pads (with wear sensor). For change front brake pads you must raise vehicle, remove wheels, extract the retaining spring of the caliper, and remove the caliper as follow: 1. Do not disconnect the brake hose from the caliper, and do not allow the caliper to hang by the brake hose! 2. Remove top and bottom caps (on back side of the caliper) for access to guide pins, then unbolt and remove them from the brake carrier. Remove the caliper. 3. Now you must thoroughly clean the brake calipers (free of grease). 4. Remove outer brake pad from brake carrier. 5. Pull inner brake pad out of brake caliper piston. 6. Check up the brake fluid level on the reservor, and emptying if neccessary! 7. Push piston back into brake caliper housing. 8. Install inner brake pad (with expanding spring) in brake caliper piston. (Arrow marked on pad - if exist, must point in direction of brake disc rotation when vehicle is moving forward). 9. Install outer brake pad into brake carrier. 10. Bolt brake caliper housing to brake carrier using two guide pins. Tightening torque is 25 Nm. 11. Install both caps. 12. Insert retaining spring into brake caliper housing. Important: Depress the brake pedal firmly several times while the car is stationary so that the brake pads adjust to their normal operating positions!!! Check brake fluid level and top up if neccessary!!!

If the brake lines and fluid is clear then you may have to look at the brake booster found at the other end of the brake pedal under the hood...

as long as it is foamy it indicates you have air trapped inside that one caliper make sure that the bleeder valve is closing all the way chances are you are sucking air back into the caliper through the bleeder or you have a leaking brake hose or even the caliper ccould be leaking, basicaly look for fluid leaks

check the brake fluid level and if it is at the proper level then there is a problem with either your sensor or the brakes themselves check the pads first does the pedal shake when you press the brakes?