rear defrost

Ok so simply connect this to the negative side of the rear defrost relay and it should work. Do I need a relay to boost the ground signal and/or do I need to diode isolate this wire from the rest of the circuit? I don't think I need a diode but i'm still learning.

On a side note what did you guys/gals use to learn how to do all this and what to use where?

Some of us used meters and test lights.  Some of us use the internet.   When some of us began doing this, Al Gore had not even thought about the internet.  We had no choice but to use a voltmeter to determine which wire did what function. 

Good Ol Al Gore...... I have been researching but there is just so much information out there it gets confusing and then trying to figure out what rating of a diode to use and type just seems like I will never get a grasp on it.

Ok so just use a relay to boost the ground and also will work to isolate the circuit and would look something like

85 R/S rear defog wire                                          

86 12 v const

87 to r/s ground

30 ground

I read earlier that you may want to be able to turn the defrost on without the vehicle being remote started.  The only way that this would be possible is if you caught the defrost wire between the relay and the defrost element on the rear window.  Grounding the defrost relay's trigger wire will not work if the vehicle is not turned on.

For what we use diodes for, the only rating that matters is the current capacity of the diode.  If using it on the coil wire of a relay, a 1 amp diode 1N4001, or any thing between there and a 1N4007 will work fine.  If using it to isolate or power left and right parking lamps, a 3 amp or a 6 amp is more of what you would need.  Radio Shack sells 1 amp and 3 amp diodes.  You can parallel 2 of the 3 amp devices to achieve a 6 amp capacity.

I was thinking about doing this but it isn't that big of an issue and you are correct becuase the relay for the rear defog runs off 12v switched.

I put the wrong wire I meant to say 87 to rear defog relay

does 85 and 86 matter which is positive and which is negative?