Sounds like you have an issue with a leaking vacuum line. Without knowing the type of vehicle, I'd say that there's a good chance that your power brakes are vacuum assisted. When you apply the brakes, you may be using up what vacuum you are still able to produce in spite of the leak. When you have a vacuum leak, it usually causes other problems, such as rough or otherwise difficult idle. It might be worth inspecting what you can to make sure everything is in place, with no lines cracked from age, or melted by laying against the exhaust manifold or exhaust piping, or, once I saw where battery acid had eaten through a vacuum line ran under the battery box. , Good luck. :-)
In most cases controlled by rear window defogger switch
It's the driver's window defogger
Not sure about the '76, but the rear window defogger switch on my 1970 Coupe is located at about seat level on the left side of the center console (tunnel) cover. It is about 6" to 7" off the floor and just under the dashboard.
Some rear window defoggers are filaments built into the rear window that heat up when the rear defogger is turned on. This type of window should not be scraped with an ice scraper.
Turn on the ac if you have it.
In my case the switch to the defogger was fried and had to be replaced. I would first determine where the problem is, then get a haynes manual and see how hard it might be to fix the problem yourself. If you can't do it then take it to the dealer.
The heated mirrors on my 1999 Subaru Forester are controlled by the rear window defogger switch which is located in the dashboard console above the heater controls and to the right of the hazard flasher switch. I'm not sure whether the heated mirrors were optional on the early Foresters or not. Anyway, the heated mirrors (and the rear window defogger) will stay on for about 15 minutes when you press the switch. You can turn them off before then if everything has defogged already. Also, the switch only works with the ignition on.
Not sure of the actual intent but in the S10 Blazers the power heated mirrors are turned on with the same switch that turns on the rear window defogger
Not all 91 Caprices came with rear window defrosters. You have to look in the glass in the back window to see if it has the small wires inside. The switch is usually on the right side of the climate control panel under the radio.
The little red, almost rust colored, lines in the rear window of many cars is the Rear Window Defogger. Sometimes, this is also referred to as a "Defroster". When the Rear Window Defogger is activated, a small amount of electricity is applied to those red lines, which causes them to increase in heat temperature. In turn, this will help to warm up the glass surrounding the wires, which in turn helps to de-ice or de-fog the window.
There is a switch on the dashboard to turn on the rear window defroster (also called a rear window defogger in areas that don't have frost). If you cannot locate the switch, take the vehicle to a local dealer of that product, and someone will be happy to show you where the switch is located. If you locate the switch and the defroster will not work, there is likely a blown fuse or faulty wiring, in which case your local dealer will be even happier to repair it for you - for an appropriate fee.
the rear window above the defogger
The fuse for the rear defogger is located behind the glove box. Just had mine replaced.
As most vehicle defogger controls operate in a similar manner, and as I'm not familiar with your make and model, this answer will be generic in nature. Rear defoggers generally draw a fairly large amount of current, and therefore that current does not pass through the cabin control switch. That switch controls a special type of relay [a time delay relay]. When you press the switch to turn the defogger on, an electrical pulse is sent to the time delay relay which closes, passing electrical current to the defogger grid. Within the relay is a timing circuit which, after a finite period of time, is supposed to release, and open the relay switch contacts, turning off the current to the defogger. From your question, I suspect that your defogger relay has FAILED IN THE ON POSITION. Usually, this failure is fatal to the relay, which must be replaced. I have a Buick Century wagon 1996, and I ran into this problem. Have you noticed if the defogger switch lights up when you hit the brake? If so, you have a bad connection somewhere. The center brake light is on the same circuit as the defogger, so you may notice that the center brake light does not light up when you hit the brake. So if this is what's happenning to you, you either have a burned out center brake light, or the defogger terminals in the rear window aren't making a good clean connection. They are located on either side of the window near the top. What I did to fix this was to solder a small piece of metal to the terminal that was not connecting and it was thick enough to make the connection. So the center brake light works, and the defogger now works exactly as it should. Hope this helps.
They make kits that are sold in most autoparts stores for repairing the broken wires on the rear defogger. Pretty inexpensive.
in the rear of the car maby?
my back brakes lights won't work but the one in the back window does
You can find a wiring diagram for the rear window defogger in a 1995 Ford Escort LX Haynes repair manual. The book is available at most auto parts stores.
It's in the top of the rear window, it almost looks like the defogger wires, except it's not a straight wire. Note: If you are having FM reception problems, especially when the rear window defogger is on, it could be that one (or more) of the defogger wires are broken. It'll be in one of two places. The Windwhield or Rear Window. It's a wire inside of the glass. Hope this helps. tj
http://www.frostfighter.com/prt2600.htm see this above link for a replacement kit: http://www.frostfighter.com/prt2600.htm
where is the rear window defroster relay located in a 2004 Toyota Four Runner, would this also control the rear wiper arm? Try something simple: just open and re-close the rear window. The window has a safety switch that keeps the wiper, washer and heater from working if the window is open. The window settles down (from opening and closing the hatch) over time the window settling triggers the switch. If you open and re-close the window it resets the switch and everything works again. My 2003 4 Runner does this over time. I just open it and re-close it to fix the problem.
Remove the decorative cover to the window switch panel. Remove the window switch retaining screws. Remove the wiring harness from the back of the window switch. Reverse the process to install the new window switch.
This is normally a resistive heating fixed to the inner surface of the glass of the rear screen.
Read your owner's manual. This information can be found there. No its not, it just shows where the fuse box is under the engine hood. I can't read which one is for rear wiper, or rear defogger. If you are unable to use the rear wiper and defogger, it is likely due to the fact that the rear window is down ever so slightly. I fought this problem for weeks until I rolled the window down and back up. Now the defogger and wiper work!!!