Im hearing 2 different things here.. So im asking help from people who have actually delt with defogging issues before, I own an 88 firebird, 305 tbi. I read through some threads and some people claim the the switch has a relay built in.. Im not so sure thats the case for my 88. I've heard there is a relay under the passenger side dash near the ecm. Is this correct? and if anyone could provide a picture it would be great thanks.

 

Another '88 305 TBI Bird I'm looking at various wiring diagrams and getting the impression that the relay is internal in the switch. As you press the button, the light it supposed to light up and you hear a *click*, that is your relay activating, if you don't get that click anymore, then there is a possiblity that your switch is bad, but to be sure of this, you need to test the ground to the switch and the power to the switch. Not positive of the colors of the wires but there should be two powers (one constant from the battery, and one from acc that is activated when you put the ignition in the "on" position) and a ground. You can simply guess and test these really, black is your ground, one should give you 12 volts all the time with the car off, and when you turn the car into the on position, you should get a second 12 volt wire, of which you can test by shutting the ignition off to see if it goes out.

If those checked out then your most likely looking at a new switch, and my best suggestion to you is if you don't want to deal with the possiblity of having to replace this again any time soon (cause anyone who has played with the dash of a firebird knows how much fun it is, lol ), then i would suggest new from either www.topdownsolutions.com or a new site i've found to have decent electronics is http://www.moderndaymuscle.com/firebird. Then again I have had the good fortune of being able to get by with my 18-23 year old rear defogger buttons with no issues, so I don't think they are commonly going, but if you were insecure about taking your dash apart in the first place, you aren't going to want to do it multiple times. Yet if you can go to a junker and get one for free, go for it, like i said i've been through at least 9 third gens and not one has given me an issue with the rear defogger, so there is a bit of quality in them.

IF!!! you still get the click and the switch lights up, then you are going to want to turn on the rear defogger (car in the on position and the light on the switch turning on with a *click*), you are going to want to test the leads in the rear defogger with a digital volt meter to make sure you are getting 12 volts back there. If it's simply the switch turns on as it should but you get no results in the back, it might have something to do with your window which you will want to check your rear window grid to make sure there are no breaks in the lines and make sure that the wires going through your hatch rods are properly secured.

I've been laying underneath the driver side and passenger side of my dash for the past week putting in power windows/locks/mirrors and the only relay that i know is by the ECM is the place that the hatch release relay goes, and that is tucked right underneath the passenger panel. Hope this is some help, sorry for the book, trying to help you out all at once instead of dragging it out...Good Luck!

 

In the 82 Camaro the defogger control was a solid state unit that included the "relay" function and switch to provide power to the wire grid on the window. The entire unit was mounted in the dash, with the solid state part behind the dash, right behind the visible switch. The control portion was a timer that powered the grid for 10 minutes and shut off power to the grid after that. You could turn the switch back on but it would only stay powered for 5 minutes the second time. You had to turn the ignition off to reset the control after that.

Power for the control portion of the unit was from the GUAGES fuse (hot with the ignition in run). Power for the window grid was from the POW ACC circuit breaker, via the Fisher junction block. I am not sure if GM still used the Fisher junction block in the 88 model year. The wire color was Orange/Black and was hot all the time. So make sure you POW ACC circuit breaker is not tripped. It is a 30 amp unit located on the fuse block.

I expect GM used the same switch/control unit for all years of the thrid gen production, but I don't know that for a fact.

So check you fuses/circuit breaker, grid wires, and power to/from the switch as 84redta suggested.

Dave

 

In Camaros the relay is built into the switch. However, in firebirds, the relay is mounted under the passenger side dash near the ECM. Its a smaller (2''x4'' ish) silver box screwed onto the dash.

 

Yeah thats what I thought Titan, thanks. Now I just need the energy to pull the dash off and im all set. what was happening is it would turn on for like a minute, it would start to defog. but it would shut itself off before the job was done.. As I also understand I dont beleive there is a sensor, I think the relay is just programed for the 10 minutes or so then it shuts off, and I beleive everytime after that its 5 minutes or less...something like that anyway.
But yeah thanks for the help guys ill install a new relay and let ya know if it fixed the problem.