Beginner seeks assistance

[Johnny7]

Greetings,
After a long period of lurking (and learning by assimilation) I have a concrete question on a trivial matter.
While going through an estate, I found this NOS Radio Shack (Micronta) digital car clock from about 1980 -- it was a state of the art gadget at the time!
My car is just new enough to not need such a device, but in trying to get it to work (no manual) I realized that I had no sure way to tell how to wire it up.
I can guess that the black (fused) wire is ground and the red is power. But there are two more.
Assuming one goes to ignition (?) what is last one for?
I have a 12VDC wall wart, but didn't just want to hook it up and possibly fry it.

Can anyone shed some light on this? Thank you in advance.

 

[Pommie]

I would guess that the forth wire is to do with headlights. The display illumination will be less at night.

Mike.

 

[upand_at_them]

Second half of this video:

If you can't make it out, contact the video author.

You won't get the tach to work on a modern car and trying to do so could damage the car.

[another] Mike

 

[upand_at_them]

Clock manual, maybe: http://www.vintagemanuals.com/manual/Radio+Shack/63-833

 

[Johnny7]

I would guess that the forth wire is to do with headlights. The display illumination will be less at night.

Mike.

Appreciate the response Mike.
However I suspect that's what the little white circular window is for -- a sensor

 

[Johnny7]

Second half of this video:

If you can't make it out, contact the video author.

You won't get the tach to work on a modern car and trying to do so could damage the car.

[another] Mike

Thanks for this (another) Mike, and the manual link too!

 

[Alxender]

Second half of this video:

If you can't make it out, contact the video author.

You won't get the tach to work on a modern car and trying to do so could damage the car.

[another] Mike

Great video. Useful for me.