I was at the wrecking yard today getting some parts for my daughters car. I found a few cars that had the rear view mirrors with On Star, Home Link and compass. I know I can't wire up On Star to a 1978 Corvette but I was wondering if the Compass was internal in the mirror or is that just a display on the mirror and there is another box somewhere in the car. The ones on the mid 2000 Cadillacs look like they mount with the same windshield button. Anyone know?

 

It's a simple 4 wire hook-up. Power -ground and two wires to the temp sensor. The compass is in the base of the mount.


Do a search for the Gentex 177. I bought mine off eBay for $30 in excellent condition. Make sure it comes w/ the 7 pin harness. New- sensors are like $25...I have the part# on my home/office computer if you need it.


I put mine on a 71- so I had to to a little modding of the mount to work on the windshield header.

 

Pretty cool idea! Is there one that works with a traditional mirror button? Would be pretty easy to get power and ground from the dome light.

 

Dome lite power is constant 12v

 

Valid

 

I installed a Donnelly mirror. Has compass,temp, auto darkening , and map lights. It is a little smaller then the gentex 177

 

Have you got the dimensions and a model number?


I wasn't aware of the smaller Donnelly- The Gentex are 10½"- and the Vettes 74-82 are 10". 69-73 are 8½" The vettes are windshield mount from late 76.

My solution for the smaller years is to use the 74-76 sunvisors.

When I researched the mirrors- Gentex and Magna/Donnelly both are GM suppliers. and have the same harness/ wiring




Here's the wiring for the 7 pin-

GM wire harness color function

PIN 1 PINK POWER +12 volts

PIN 2 BK CHASSIS, GND

PIN 3 LT GRN BACKUP LIGHTS

PIN 4 GY TO AUTO DIM OUTSIDE MIRROR

PIN 5 PINK TO AUTO DIM OUTSIDE MIRROR

PIN 6 DR GRN/WT TEMP PROBE

PIN 7 BK/WT TEMP PROBE

Note: Pin 3 is to be connected to the backup lights to turn off the auto dim feature in reverse. If you intend not to use this feature connect the LT GRN wire to chassis ground. If this pin is floating the auto dim will not work properly.

 

I don't have a part number. But here is a picture of it. It measures 9-15/16" across and 3-1/2" wide.

 

Thanx for all the responses! I'll hit up the wrecking yard again on Monday see if I can find one without the OnStar buttons.

 

Look for a 03 to 06 sierra. I just got mine this week. It has compass and temp. The temp sensor is in the middle of the grill near the bottom.

 

I put one from a gm pickup in my 74. I removed the factory mirror bracket and glued on the piece for the new mirror on the windshield. Compass is built in the mirror. Easy mod and works great.

 

I really like this upgrade idea. I wonder if you could place the temp sensor somewhere under the hood to monitor engine compartment temps? They may get too high for the sensor to handle.