I am trying to understand the wiring functions in the overhead/dome light.  I have studied the FSM (Figure BE-23) and the wiring to my light to find out why my light does not work by door contact or manual (lens button).  I am trying to use my very basic electrical knowledge and use my voltage tester to determine energized and grounded wires.  I clearly test the Blue/white stripe wire as constant 12 volt,  battery powered.     I also get a functioning ground signal from the black wire. The bulb (even tried several) tests as good.  However, I can't get any power across the bulb connections...BW (BE-23 code LW) and Black/red stripe.  I know that BR is controlled by door switches, however, my connected, or disconnected, bulb terminal or open/closed doors the BR won't allow power to body ground B allowing bulb to light.  Isn't the actual function of the BR wire to create/allow a full grounding at the bulb based on door switch button in/out?  To test the door switches, does the BR get any energy to voltage test against B?  I see a closed circuit/loop for the BR from the light terminal (with RH and LH split) to each door switch and back with no power to BR...so how would I test each switch?  Yes, the LH switch also has a Black and white stripe power and Black ground wires but the switch seems to have two separate circuits for dome light and theft protection and no power shared to BR.  Please no flames my confusion but kindly help me to understand switch testing and why BR bulb terminal connection won't close loop allowing LW power to B and allowing light to work manually with door closed. Thank you, for your patience; I'm trying?

Edited June 30, 20177 yr by Packerz

If you can measure power and you can confirm ground then you should get light.  You forgot to describe the year of car - 1977.

B is on a switch that's right there at the light.  It's push-on, push-off switch.  BR runs through the door switches, which are only closed when the door is open.  But they do get stuck.  Mine were and needed some contact cleaner and working back and forth to get right.

You might just hook your meter up to B and/or BR and work the switches to make sure the ground is good.  That's all that they do, supply the ground.  If you have power to the terminal at the bulb that's connected to blue/white then the problem has to be the grounding.

I copied the page from what I think might be the 1976 FSM, not really sure.  I know I sent you to Mike's copy but I'm not really sure what year that is and don't want to run the application that's required to unzip it.  I got mine from nicoclub.com

Anyway, here it is.  It's probably the same. It matches your wire colors too, but it's on a different page.

 

Edited June 30, 20177 yr by Zed Head

Thank you, again Zed Head. You confirmed my thought that BR really functions as ground wire to/from switch (es)...Black grounds the switch itself and BR sends ground signal to light terminal? Yes I still have to "chisel" door switches out to verify solid ground and probably solve bulb operation during door open-button release.  I still have to ask why BR and door switch affects even the manual lens button operation of bulb.  Sincerely not to belabor the point, but doesn't the B (constant body ground) terminal make a direct connection with BR terminal and ground side of bulb holder?  Even if the BR wire wasn't connected to its terminal... wouldn't the bulb holder's connection with black terminal work for "push button" operation of an installed bulb with constant 12volts at opposite bulb holder/terminal

I gotta tell you how gratifying it is for a Club member to respond in a thoughtful and kind manner.  It isn't all the time that a fellow Z actually reads the posted question being asked before flaming post response...that is if any (helpful) response to actual question is even given.  

The difference is noted and appreciated!

  On 7/1/2017 at 3:42 AM, Packerz said:

  Sincerely not to belabor the point, but doesn't the B (constant body ground) terminal make a direct connection with BR terminal and ground side of bulb holder?  Even if the BR wire wasn't connected to its terminal... wouldn't the bulb holder's connection with black terminal work for "push button" operation of an installed bulb with constant 12volts at opposite bulb holder/terminal

Can't really tell how the dome switch works.  Those types of bulb holders are often loose, I think.  Like fuse holders.  You're 90% there with your meter measurements, you just have to figure out how to get the bulb ends connected to what your meter shows.  Sometimes the poking action of the meter probe will cause a contact that goes away when the pressure is released.  If you're seeing a ground circuit though, at least you know the ground circuit is available.