Hey all,
I've had this aftermarket rear view mirror in the '75 vette for some time now but never did get around to wiring in a relay for the map light courtesy function (ie. open the doors and the map lights come on).

So, now I'm looking at a '77 courtesy light timer and considering wiring it into the circuit for the map lights on the mirror as opposed to messing with a relay. The map lights line IIRC is simply a high side trigger line. It needs +5VDC but works with +12VDC. I'm not sure of the wiring/functionality of the timer. Anyone have a diagram of how the timer is wired and/or an explanation of it's outputs?

 

The 77 electrical troubleshooting manual has the information you need. I'd scan it, but it's a huge-format book and I don't have a scanner big enough. There are six copies of the 77 book on eBay right now, one starting at $0.99.

 

Not such a bad idea, but the shipping for the manual is more than the price of the timer. I would do it anyway but for making a bastardized timer in my '75 the '77 manual seems like overkill.

Not sure offhand how the '75 schematic sets it up but with the open ground courtesy light circuit going to the door switches, I'm trying to avoid putting a relay inline in case voltage drop plays a factor. Besides the timer gives me extra features, seems a more electrically elegant solution, and based on the pics below, may not drop the voltage:




'Twould appear to be 1 orange wire to +12, 1 black wire to ground, and the other 2 remaining wires inline in the open ground courtesy circuit.

Hmmm, since the module has it's own independent power and ground, and IF the '77 lighting also operates with the same open ground.... I would have to assume it simply triggers, then uses it's own independent power to maintain a courtesy circuit ground for a timed period via it's own ground...... Hmmm..... may not be suitable to kick a high side signal to my map lights afterall..... Then again, unless it's just old tech stuff, that could be accomplished with a 3 wire module.....I may just get it and wire it in for the sake of the other courtesy lights tho. If it works one way it'll power my map lights, the other way and it powers my other courtesy lights. I suppose I could just tap a chip off the line with and inverter, door switch grounds the line, tap drops low and sends a high to the map lights.....

Sorry to meander. Should have disconnected my fingers while my brain was idling

 

If you’re main concern is the shipping charges for the electrical troubleshooting manual, I will pay you double the shipping charges they want for the manual + actual shipping charges for your timer assembly.

 

"The COURTESY LIGHT and Dome Light delay operation is added by separating C121 and connecting the white and white/black wire as shown."

That's under dash above speedo in the small pic. you posted.

"ORANGE WIRE - PLUGS INTO CAVITY MARKED 'BAT' "

 

Ahhhh....... huh?

Timer is an Ebay deal $10 (so far)and shipping.
Manual is also on Ebay $.99 and $13.05 shipping.

Shipping charges don't bother me per se. It just feels kind of silly to own a '75, buy the '77 timer, and then spend $14.04 for a '77 electrical manual of which a single page would ever have any relevance to my life, in addition to taking up space in my admittedly already cluttered house.

 

I doubt that timer assembly will stay cheap, unless it's seriously mis-listed. Those things have been obsolete for years, and when I was trying to replace my original, breakers wanted $65 or so for a used timer. You may have noticed that another seller has the same NOS assembly listed with a $150 Buy it Now price. I built a solid-state replacement, slightly modified from these instructions: http://sound.westhost.com/appnotes/an004.htm Cost about $10 in parts from Radio Shack.

 

Some GM cars and trucks have the timer built into the mirror. I know 92-94 S series trucks had them. It was a four wire hookup
12v batt
12v ign
gnd
White trigger from dome light sw.