Rear Window Defroster Help

[CaliLove692]

I just finished doing a dash swap from an 04 Mach 1 into my 99 GT and got everything to work except for the rear window defrost switch. I replaced the switches from their original location for TRAC OFF, FOGLIGHTS, and REAR DEFROST and wired all of them to the newer style switches under the radio. I was able to get the TRAC OFF and FOGLIGHT switches to work no problems, but for the REAR DEFROST switch I am having problems. I cut the switch off the harness the car originally came with and extended the wires to the new switch. Now the only thing the switch responds to is if I turn the headlights or parking lights on (it will illuminate) but if you press the switch it won't turn the defroster on. Does anyone know what to do to make the switch work??

Heres the connections I have so far, I have the LB/RD extended to the LB/RD of the new switch, thin BK (ground) connected to the BK of the new switch, PK/LB to PK/LB of the new switch, BN/LB connected to the relay from the 04 wiring harness then the BN/LB spliced into that, thick BK connected to BK on the relay. Only wires remaining are a YE/BK from the relay which says goes to the instrument cluster but I don't see that wire in that harness. The other wire is a BK/YE from the new switch which says goes to the cluster (there is a BK/YE in the cluster harness but need to know if that is the right wire to tap into.

Here are the diagrams for both years:
1999 Defrost wiring diagram:
http://img83.imageshack.us/img83/4529/19996dl.jpg

2003 Defrost wiring diagram:

http://img83.imageshack.us/img83/7760/20034me.jpg

Thanks...

 

[Kilgore Trout]

Have you closely inspected the rear window wires and connections to the rear window? The problem could actually be back there... All of it is repairable, even the metal strips adhered to the glass that heat up. Those strips commonly get broken.

 

[CaliLove692]

everything was working fine with the 99 style switch before I did the conversion to the 04 dash the other day. I got the new switch to illuminate green when the headlights are on but the switch doesn't turn the defroster on with the indicator light. I'm pretty sure that after I get the YE/BK and BK/YE wires attached it should work but have no clue as to wire to tap those wires into.

 

[CaliLove692]

Does my 99 already have a relay for the defroster if so do I need the one off the 04 and if so how do I wire up the new 04 switch to make it turn on and off the defroster?

 

[Mike97gt]

your problem is in the 99 mustang they used a smart rear window defrost switch that did not feed into the instrument cluster. in the 2003 they used a basic switch to "tell" the instrument cluster module to activate the rear window defrost relay. in the 2003 the only thing that is the same is the ilum. all the other wiring and what part controls the system is different

I assume you are using the 99 cluster in your car? it will be way to complicated if not impossible to make the 2003 cluster work in your car. and it will be kind of complex to make the 2003 switch work with the 99. you might have to make the 2003 switch activate the 99 switch that will be hidden in the console area.

and you can't just "tap" into the same colored wires on the 99 harness. even if it went to the right pin in the cluster, the 99 cluster will not have the logic built in to control the rear window defroster.

if i was you i would hide the 99 switch inside the console and use the 99 switch. leave the 2003 switch wired to light up and not do anything.

 

[CaliLove692]

how could I make the 03 style switch activate and control the 99 switch?

 

[CaliLove692]

is there any other way to activate the 01-04 rear defrost relay, I have the entire dash harness from an 04 the dash came with laying around, if not is it possible for me to get the switch to work if I were to use an 04 instrument cluster? (I have the entire cluster from an 04 Saleen but am only using everything from the cluster besides the circuit board..., I still have the circuit board from the cluster though)
Thanks

 

[CaliLove692]

I know I would have to take the car to the dealership to get pats cleared if I were to swap the circuit board in the cluster.

 

[03 Black GT]

one of my defrosters broke off the glass. How can i adhere it back onto the window?

 

[Kilgore Trout]

one of my defrosters broke off the glass. How can i adhere it back onto the window?

The technique is described in the Haynes manual. It requires a repair kit and you mask with tape and then "paint" on a new metal strip between the tape masking.

 

[Mike97gt]

i would not try and get the 04 cluster to work in your car.first thing is who is going to programm them to work as far as the pats go, that is beyond what a dealer can do. the wds software will not allow them to program it correctly

the HEC module ( instrument cluster) is vital to the car. it is the network hub for the communications of all the cars modules. all of the modules need to match with the cluster to work properly.

if i was you i would hid the 99 sytle switch in the console and just use that for the reardefogger, and just leave the 04 switch in as a dummy. it is not worth the hassle and cost to get it working with the new style switch.

 

[Mike97gt]

how could I make the 03 style switch activate and control the 99 switch?

it wuld require you to disassemble the 99 switch and wie directly into it to bypass the button on the 99 switch..

can be done but not worth the hassle

 

[n0v8or]

svttech76's description of the differences is 100% correct. The '99 switch contains a relay and timer (usually ~10minutes) that automatically turns off the defroster. In the '03/'04 the relay and timer are located elsewhere in the car.

I don't see any way to make the new switch activiate the old one. However, if you are willing to give up the timed automatic shutoff feature, I can show you how to wire a $5-$6 Bosch automotive relay and 2 diodes to make the new switch operate the defroster manually. Once, on, it will stay on until you turn off the ignition, long after the window is clear. It will always be off when the ignition is off, so you won't drain your battery.

The relay and diodes can be taped to the switch harness with electrical tape.

Along the lines of the solution svttech76 recommended, perhaps you could mount the origiinal switch on the panel directly behind the shifter, then it would work just as it did before. The new switch would be a dummy.

 

[CaliLove692]

n0v8or can you tell me how to wire up a relay and diode to make the new switch work. I don't care about the automatic shutoff. Thanks

 

[n0v8or]

OK. I'll post it tonight when I get home from work.

 

[Mike97gt]

svttech76's description of the differences is 100% correct. The '99 switch contains a relay and timer (usually ~10minutes) that automatically turns off the defroster. In the '03/'04 the relay and timer are located elsewhere in the car.

I don't see any way to make the new switch activiate the old one. However, if you are willing to give up the timed automatic shutoff feature, I can show you how to wire a $5-$6 Bosch automotive relay and 2 diodes to make the new switch operate the defroster manually. Once, on, it will stay on until you turn off the ignition, long after the window is clear. It will always be off when the ignition is off, so you won't drain your battery.

The relay and diodes can be taped to the switch harness with electrical tape.

Along the lines of the solution svttech76 recommended, perhaps you could mount the origiinal switch on the panel directly behind the shifter, then it would work just as it did before. The new switch would be a dummy.

yeah you can do this too . just remember to turn off the defroster yourself when it clears the window.

 

[CaliLove692]

so how do I go about making the switch work this way and what do I need to get?

 

[CaliLove692]

The wiring to the 99 switch is as follows:

12 gauge BN/LB wire that runs to the defrost grid
12 gauge BK wire thats hot at all times running to the battery junction box
18 gauge PK/LB wire that runs to the central junction box
18 gauge BK wire that goes to ground
18 gauge LB/RD wire that goes to illumination

 

[CaliLove692]

would I be able to use the relay from the 04 harness to tap into the right wires to make it work?

 

[n0v8or]

The reason a simple circuit won't work is that the '03 - '04 switch is only a momentary contact type. You would have to hold it in to maintain power to the relay and defrost grid. Not very convenient. What I proposed is a latching relay circuit that does the equivalent of holding the button in once you press it. The downside of this approach is that the only way to turn off the defroster, once on, is to turn off the ignition. These grids draw ~20amps and are not designed to be operated for more than 15 minutes continuously. In addition, the extra drain on your alternator will shorten its life. Unless most of your trips are 10 minutes or less, I now agree that Svttech76's suggestion to tap into the old switch is probably a much better idea (this is not the first time he has a better idea than I do). Assuming the '99 switch is also momentary contact, its just a matter of bringing out a single wire, which would then go to the '04 switch. The '04 switch and indicator would then operate just like the '99, and you would not need any relays or diodes. The old switch assembly could be taped to a harness behind the new one. If you would prefer not to take the switch apart, PM me and I can get it done for you (I work in an electronics lab where we design automotive electrical parts). Your only cost would be 1 way postage to the East coast.