Author Topic: Rear window earth point (Read 3643 times)

carlos318is · « **on:** March 04, 2009, 10:44:40 AM »

Does any one know where it is as I have 12volts going to it but the window will not demist

Many thanks

Sorry its a E30 318is

Cobra Jet · « **Reply #1 on:** March 04, 2009, 12:15:02 PM »

are you sure that the defogger lines or grids have not been slightly damaged or cut through? If there is the slightest scratch or scrape across a single grid line, that line (or multiple lines if multiple are damaged) will not heat up to demist or defrost the rear window...

There are defogger repair kits- which consists of a small bottle of repair compound. You have to find the problematic grid (easiest done by shining a flashlight from behind the grid, or placing a solid white towel or paper over the rear window) - this will reveal any grids that have been damaged (you will see a very fine break in the grid line, the paper or light helps to show the damage better). Once you find the break, you use a small brush and brush the repair compound onto the line... After the compound dries, you turn on the rear defogger and those repaired lines should then work...

Here is a link to the repair kit:
http://www.permatex.com/products/Automotive/specialized_maintenance_repair/auto_glass_lens_repair/Permatex_Quick_Grid_Rear_Window_Defogger_Repair_Kit.htm

most defogger lines get damaged if someone has removed window tint (it peels off the metallic copper coating on the grid lines, which renders the line or lines inoperable even if power is getting to the line) - or if someone has used a scraper or razor blade on the interior side of the window - that also scrapes or damages the grid lines...

I hope this was helpful - (obviously if you have no rear defogger grid lines in the rear window, like on a convertible - my above fix or help is meaningless.... LOL - as those vehicles have a blower motor or fan located behind the top portion of the rear seat, which blows hot air onto the rear window for defogging/demisting).

ak96ss · « **Reply #2 on:** March 04, 2009, 12:43:48 PM »

I'd actually start with checking continuity across the grid to make sure that it is in one piece.

carlos318is · « **Reply #3 on:** March 05, 2009, 07:24:46 AM »

All the lines are ok I have looked at them and not even 1 line heats up:( so all I could think of was the earth:confused:

ak96ss · « **Reply #4 on:** March 05, 2009, 10:19:51 AM »

The one that was in my car originally looked fine, too, but only half of it would heat up. In the end I bought new glass - mine exploded on the way to work one cold morning. I guess it was the temperature differential that did it in, half the glass toasty and half freezing. I repaired some of the grid beforehand with that goop, but it didn't work for rebuilding the whole grid...

Again, check continuity of the grid. There may be breaks that you just can't see, or it may just be that it is old...

ak96ss · « **Reply #5 on:** March 05, 2009, 10:20:22 AM »

Actually, I'd make sure you were getting +12V at the connector first...

carlos318is · « **Reply #6 on:** March 05, 2009, 10:30:53 AM »

I have looked I am getting 12volts at the window

romeomike · « **Reply #7 on:** April 02, 2009, 09:27:15 PM »

According to Chilton and the ETM, the ground point is G300, under the rear seat on the left hand side.