Lost 12V Ground 1 circuit Interior Lights, Ideas on finding

While Changing out Vent fan Motor in Lavatory I lost power to the circuit. This also includes 5 other Overhead Lights on same circuit.

Fuse is not blown (I have a PD4645 Converter/ charger).

In running test with my Multimeter, IF I attach a temporary ground (Length of wire/alligator clips) to the Negative side of the wire intended for the vent fan to the PD4645 case (Only because this is the only close ground source I can find, I show proper voltage (12.6 Plus depending on PD4645 charge Mode).

Second Test I ran was measure voltage through the ground side of bad circuit I get 12 Volts measured on the ground side...... Isn't this an Indication of a shorted ground ?

When I attach the Temporary ground the 5 lights work as they should (I don't know about the New Vent Fan Motor as I have not tried to put back in operation).

For the life of Me I can't find the location of fault in either the Lights (I have pulled them out of the ceiling and the appear to have no shorted wires etc) OR the wiring I can access behind the fixtures.

I Have a PDF of my RV electrical schematics from Winnebago for my Motor home (WF324V) and I'm having problems finding the connectors on the wiring harness as they don't seem to be in indicated locations.

One question is do I simply need to re-establish a good ground on this 1 circuit without finding the Break ?

is there a easier way of finding the proper ground wire other than probing all the Ground wires (I know they are the WHITE colored wires) ?

Accessing the wiring within the ceiling not possible as is the wires for the circuit that I believe run from the ceiling down the interior wall. The bundle of wires appear to run under the bed which I have to remove to access. the wire bundle at this point appears to be 20 or more individual wires.

Open to words of wisdom

Getting ready for vacation next week and this is kicking my butt.

Thanks in advance

Chris_Bryant
Explorer II
Apr 10, 2019
If I am understanding you, you don’t have a short, you have an open ground.t

Edited to correct bloody iPad autocorrect mistakes
Kamphiker
Explorer
Apr 10, 2019
Chris Bryant wrote:
If I am understanding you, you don’t have a shirt, you have an open ground.

I am not 100% Positive its just a "OPEN" ground due to measuring voltage on the negative side.
YC_1
Nomad
Apr 10, 2019
You have an OPEN ground circuit.

Is it possible there was a screw through some metal mounting that you took out that was used as a ground?

Perhaps the motor mounting was being used as the ground.

It is hard to suggest where to ground without a picture but yes, making a new ground point is ok although not ideal.
Kamphiker
Explorer
Apr 10, 2019
YC 1 wrote:
You have an OPEN ground circuit.

Is it possible there was a screw through some metal mounting that you took out that was used as a ground? No, None attached

Perhaps the motor mounting was being used as the ground. No, the Previous motor was mounted to metal rail bit it was not grounded there. The Negative wire from the coach wiring loom was connected to the fan Motor Negative side and there was no connection the the frame holding it.

It is hard to suggest where to ground without a picture but yes, making a new ground point is ok although not ideal.

Figuring out how to run the new ground wire to connect past the broken ground point is where I'm stumbling.
steved28
Explorer
Apr 10, 2019
It seems removing the OEM fan was the point you lost your ground. So that would be where I would find the "new" ground. As YC 1 suggested, most likely that entire circuit receives its ground from the fan mount. If you ground the negative to the fan, do your lights work? I assume they all share the same ground?
troubledwaters
Explorer III
Apr 10, 2019
Not being able to see what exactly your dealing with wire wise, its pretty hard to diagnose over the internet. My recommendation would be to finish the fan installation completely then see if things are back to normal. With the installation half complete and things not connected that used to be connected its hard to know what is going on.
Chris_Bryant
Explorer II
Apr 10, 2019
You are measuring voltage on the ground because the ground is picking up voltage from a light that’s on. Hook one side of a light to a battery and you will assure 12 volts on the open lead. The ground is hot because it isn’t hooked to ground.
As others he sai, try installing the vent fan and go from there, which would be going back through the circuit, finding the last item that works.
pianotuna
Nomad III
Apr 10, 2019
Try putting the old fan back in. If that works--then remove and install the new fan?
wnjj
Explorer II
Apr 10, 2019
Kamphiker wrote:
Chris Bryant wrote:
If I am understanding you, you don’t have a shirt, you have an open ground.

I am not 100% Positive its just a "OPEN" ground due to measuring voltage on the negative side.

As Chris said, you are measuring the 12V through the filament of a light bulb or some other load that is trying to turn on but has no ground. Since there is no current flowing the voltage on both pins of the bulb is the same. Light bulbs are just tiny pieces of wire.
MrWizard
Moderator
Apr 10, 2019
Sounds like you crossed wired the down stream negative wires to the source feed hot positive wire

You have 2 hots running to those lights and no negative/ ground for them