Voltage drop when switch is toggled and more


Old 04-11-18, 12:02 AM
Thread Starter
Join Date: May 2017
Location: USA
Posts: 7
Received 0 Votes on 0 Posts
Voltage drop when switch is toggled and more

long story super short ... put in a new ballast in a light fixture today and could not make it work ( ballast was not new per say just been laying around so we tried it). Ballast did not work so we went into repair mode but ran into a speed bump I cannot seem to figure out so im looking for advice or direction to try next.

Put in two new switches (which I may redo tomorrow just to be sure) in the wall for the lights i was working with and got a new fixture all together. After we did a little rewiring and testing ...from what I can tell the switch setup is correct. Hot going to one terminal of one switch with a jumper to the adjacent switch for power. Then the load wires off each switch running to their appropriate fixtures. Common/whites all secured with a wire nut in the rear of the switch box.

After switch install and wiring of the fixture we got no light at all. started trying to troubleshoot a little and noticed that when the voltmeter is on the 2nd switch it reads 20v even with the switch off ... and when you turn the switch on it actually drops to 0v. The first switch reads 120 terminal to terminal and appears to be working correctly and turns of the fixture it controls. Again i will double check this wiring tomorrow but im pretty sure wires are in the correct position.

We noticed the same trend on a wire in the ceiling which I BELIEVE is the switch wire behind the fixture. The house is old and im not exactly sure I know whats going on behind the fixture but best I can tell is as follows ( also seen in picture):

One constant in the ceiling behind fixture even with the switch that should run things in the OFF position. 2 white/common wires that were together before i started tinkering. A single RED wire which after trial and error I figured out runs the garage door opener outlet in the ceiling. Lastly, another single black wire as mentioned above. I believe it to be a switch wire and when I test it, does the same thing as the switch in the wall ( starts with a low voltage around 20V and when switch is toggled drops to 0V).

Just trying to get these lights up and running again any ideas or thoughts or criticisms about how dumb I have been are all welcome. Just for the record I am NOT an electrician but I am also not totally inept either, but this one does have me a little stumped so make fun all you want I can take it! but if you have any advice im all ears I will try to post or insert a small photo collage so you can see a little more of what I am dealing with if I can figure out how LOL!

Name:  diag.jpg
Views: 153
Size:  69.3 KB
Sponsored Links
Old 04-11-18, 05:16 AM
Geochurchi's Avatar
Join Date: Nov 2012
Location: USA
Posts: 4,071
Received 19 Votes on 19 Posts
Hi, did everything work before you tried to replace the ballast, did you break any splices?
Old 04-11-18, 06:48 AM
Join Date: Mar 2010
Location: USA
Posts: 3,614
Received 24 Votes on 24 Posts
Unhook the hot wire from the light fixture that does not work for you. Then can you measure 120 volts from the now loose hot wire coming out of the ceiling box to the neutral in that box when the switch is flipped on and zero when the switch is flipped off?

You mentioned "terminal to terminal." This is not a useful measurement except for gurus and engineers and experts.

Measure voltage only from neutral to a switch terminal or from neutral to a wire of choice.

When any switch is flipped "on" the terminal to terminal voltage should drop to zero.

Turn off power before trying to measure resistance (ohms) or continuity.
Old 04-11-18, 02:02 PM
Thread Starter
Join Date: May 2017
Location: USA
Posts: 7
Received 0 Votes on 0 Posts

Update on this issue after I slept on it for a night...


I was correct in my thinking partially.... the switches were wired correctly and are BOTH working correctly.

I found that the constant for the switches i was dealing with was actually coming from the box in the ceiling that went through the garage door opener outlet and then looped back to the wall to provide power to the switch box.

So basically in the ceiling where things got crazy I found a constant power that fed the garage outlet wire which fed the switches. Then we had the 2 sets of common wires in the ceiling box, easy enough to tie them together. Then we had the additional single black wire I found was the actual SWITCHED wire from the switch box.

So I made my connections in the ceiling box from the wires that needed constant power, tied my common/whites together with a pigtail down for my light fixture. Also connected my now correctly functioning single switched wire in the ceiling box with a pigtail down for the fixture. Metered it out showed correct, mounted my fixture and made all connections, flipped my switch.... and ... BOOM GOES THE DYNAMITE! SHE LIVES!!! If any of that makes sense haha....

I appreciate any and all the help and suggestions I got! Once I figured out what was what... and that the wire in the ceiling was also the wire at the wall .... the pieces fell together and I got it all to work. Score one for the day... now its time for a freakin nap!!! LOL

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

Thread Tools
Search this Thread
Display Modes
Ask a Question
Question Title:
Your question will be posted in: