No Heat - Passenger Convex Mirror

[thom4782]

Hi all:

I have several questions, but first here's the background

1. Purchased 1987 944 Turbo last July
2. Never tried mirror heating function
3. Replaced 'flat' passenger side mirror with 'convex' mirror
4. Tried using mirror heating for the 1st time this December
5. Driver side mirror warm to touch; passenger side mirror cold
6. Removed 1st convex mirror, which was held in place with thin adhesive pads thinking mirror was not contacting underlying base metal plate
7. Glued new convex mirror directly to the metal base using small dabs of 3M 5200 sealant along the edge at the 12, 2, 4, 6, 8 and 10 o'clock positions
8. Still no heat

I've tried some electrical diagnostics.

1. Voltage at wire connectors approximately 11.6 volts with motor off
2. Resistance across the mirror base terminals approximately 8 ohms
3. Expected a 1.5 amp current, but did not measure it before gluing in new mirror onto frame

My personal guess is the base is bad because it didn't feel very warm to the touch when I tried heating it without the mirror glass in place. Frankly, I was surprised at the 6 ohm resistance. I would have through it would have been close to zero.

So here are my questions

1. Do you think the mounting base is defective given the electrical values
2. If you think its OK, do you think the issue may be that the mirror is still not contacting the metal base thus failing to transfer the heat to the glass
3. If the problem is a gap because the mirror back is slightly convex, would placing a piece of aluminum foil between the base and the glass likely fix the problem
4. Finally, does anyone know the type and size of the connectors at the end of the wires.

Thanks for any help you can provide. The increased visibility from the convex mirror is worth the loss of heating, but I'd like both features if I can have them.

Thom

[thom4782]

Well, I gave up on going down the replace with convex glass route. Instead, I found Porsche actually sold a heated convex passenger mirror for my car - 944-731-035-06. While the Porsche documentation is confusing because it leaves my 87 model out of the technical description, the Porsche dealer tells me its an exact fit. We'll find out next weekend when the new convex mirror with its base arrives.

[curtisr]

I wonder if the heating element isn't toast.

[thom4782]

Problem fixed...

As noted above, I tried just to replace the mirror glass. While there was a huge improvement in visibility, the new glass never heated.

The fix turned out to be simple. Porsche actually sells a convex passenger side mirror for my 87 turbo. The part number is 944 731 035 06.

I popped it in this morning and voila heat. Yea!

I'm not sure why the aftermarket glass replacement approach never worked. The only information I have is the glass only resistance across the base terminals was 8 ohms and the Porsche part's resistance was about 2 ohms. Maybe the increase current made the difference

Hope this helps.

[DannoXYZ]

Well... With those numbers, factory element should draw 4x the power and generate 4x as much heat. Could be defective heating element. Did you ever measure mirror on other side to compare?

[thom4782]

I only measured the passenger side. I'll check the driver side one sunny day and report back.

Unfortunately, I didn't think of taking measurements on the passenger side before I removed the flat glass. For all I know, I may have caused a problem when removing the glass.