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12volt mystery

Happy Fourth of July,
Hopefully one of the gurus on the forum will be able to clear up this mystery for me.  The florescent ceiling fixture between the refrig and the cupboard stopped working.  I checked the voltage at the switch and at fixture and found 13v.  I assumed the fixture was bad and purchased a new one.  New fixture would not operate, so I checked both the new and old fixtures with a 12v battery and they both work.  The voltmeter reads 13v at the ceiling when the switch is on, however when I hook the fixture to the wires the voltage drops to zero.
The switch that controls this ceiling fixture is right next to the switch that controls the under cabinets lights in the cupboard.  If I take the hot wire from that switch and swap it with the ceiling switch the ceiling fixture works and the under cabinet lights do not.  How can the wire show 13v on the voltmeter and not power a fixture?

We spent the Memorial Day holiday visiting family in Dallas and then went on to Nacogdoches for a factory tour.  Had a great visit and saw a number of million dollars being built.
It gave us a new appreciation of our wonderful and 'what a bargain' 1995 U320 coach.

We had the oil in the M11 changed at the Speedco in Dallas just off the LBJ Freeway.  The manager is Mart Elder and we highly recommend their fast, efficient and friendly service
The oil change with Delo and filters was $235.  We had some unforeseen difficulties and Mart Elder went above and beyond the call of duty to help.  Good people.

Thanks,

Bud and Dale
1995 U320C 4000 WTBI
St. Louis 
Bud&Dale Pessin
2002 U320C 4220WCDS

Re: 12volt mystery

Reply #1 –
You might try to check all of the connections.  One of the reasons you are getting voltage and the light not working is the connections or wires.  If you use a very, very fine wire, you could carry the amperage that the meter needs to read.  When you put a load on it, it either blows out (a fuse) or the amperage gets choked off so badly at the bad connection (thin wire, sort of) , a traffic jam of electrons and, no light.
It could be in the switch, connections or fixture.
Try checking the voltage at the fixture when you turn it on.  An indication of the above problem is a severe drop in voltage, check the circuit.
Michael Baldacchino
'97 40' U320

Re: 12volt mystery

Reply #2 –
We need the exact details of who, what, where and when, during your testing.
Do we assume that you are measuring voltage at the fixture location by attaching your multimeter to the black wire (positive) and to the white wire (negative) that is screwed into the chassis in the roof to provide a ground connection?
Or, are there two wires in a wiring loom going to the fixture?
It is possible that the grounding screw is not allowing a good enough ground for the light to operate.  You could take the screw out, clean it and the connector and re-install and then test again.

I am not sure but, I think the relay is a mechanical relay and the contacts supplying the power to the fixture could be corroded/erroded and not supplying the amount of current needed for the fixture.  If it is the old VW type relay, you can probably change it out at a very reasonable price.
Let us know what solves the mystery.
Regards,
JON TWORK KB8RSA
Full Time RVer (10+ Years) & Dedicated Boondocker
Retired, Unemployed, Homeless Transients
1996 Foretravel U270-36 w/24' Timberwolf Trailer
I firmly believe that tomorrow holds the possibility for new technologies, astounding discoveries, and a reprieve from my remaining obligations.
Welcome to WeRV2 (Under Construction)
Find Jon: Via Satellite Tracker Datastorm Users
The Second Amendment is in place in case they ignore the others.

Re: 12volt mystery

Reply #3 –
Doesn't that light have another switch else where in the coach that controls it also.
I know on my coach the ceiling lite in the dining area has a switch by the entry door
and also over the sink, either one will turn on or off the lite.  The ceiling lite in the bath
room has a switch by the sink and one in the bedroom that does the same.  The one in the bath quit working and I went and changed the bulbs to no avail.  There is a relay that cause the two switches to work and needs to be replaced.  I got the relay from the factory but have not had time to replace it yet.  I hope I can find where it is hiding

Good luck
Jimmy Freytag,  Ardmore, Ok
1999 36ft U320. — -SOLD—-
1988 40ft GV        1990 36ft U280
1993 40ft U280      1996 36ft U280
  TRAVEL WHILE YOU CAN THE TIME WILL COME
            WHEN YOU NO LONGER CAN.

Re: 12volt mystery

Reply #4 –
To directly answer your question, this can happend when there is a "high resistance" point somewhere in that + 12 volt source.  I've seen them most commonly in crimp connections - a little bit of corrosion starts between the wire and terminal (eventhough it looks perfectly normal).  As the corrosion progresses the resistance increases until almost no current will flow through it but still enough for the meter to read full voltage.  An old fashioned "ice pick" test light where you can penetrate the wire insulation before the crimp can be handy in finding these bad terminals.  Sounds like it might be right there at the + 12 volt supply wire crimp where you did your wire swap test.

-John Fitzgerald, 1991 40' U300 SAI
John Fitzgerald
1991 U300 (SAI) Side Aisle Island Bed 40'
Detroit 6V92 with Allison Retarder
Meridian (Boise), Idaho

Re: 12volt mystery

Reply #5 –
Hi Bud & Dale,
  Our 1997 U 320 has a relay for that fixture. On ours it is behind a removable left end panel, in the storeage compartment,  right above the microwave. The left end/side panel can be removed. Had to replace it years ago. There is a 110 outlet in the same, very small, panel. Another I never knew it was there outlet.

Raymond & Babette Jordan
1997 U 320
1998 Ford Explorer XLT

Re: 12volt mystery

Reply #6 –
Thanks for the replies.  The mystery is solved thankfully, as I was getting tired of taking things apart.
I finally found a bad connection in the wall along side of the dining room cabinet.  Removal of the left side inner panel of the cabinet allowed access.  The tape hoedowns were no longer functional, so they were fixed along with the faulty connection.  Light is good.  Now on to replacing the bedroom TV with a flat panel.

On another note , we are planning on heading up to Michigan and Wisconsin, any suggestions for places to stop?
Thanks.
 
Bud&Dale Pessin
2002 U320C 4220WCDS

Re: 12volt mystery

Reply #7 –
Lake Geneva WI, Door County WI, Oshkosh WI for airshow last week of July.
Tim Fiedler    2025 LTV Unity MBL on Order
2000 Chevy Tracker 2 Door Convertible 4WD Now lifted 4.5"
1985 Citroen 2CV6 Charleston
Murphy Rebel on wheels with 175HP Titan
Cessna P337
1980 48' Westport MY (!/4 Share)

Re: 12volt mystery

Reply #8 –
Quote
We are planning on heading up to Wisconsin, any suggestions for places to stop?

We really enjoyed "The House on the Rock" in Wisconsin.
So many collections of so many things.
We were there 5 hours and that was not nearly enough time.

http://www.thehouseontherock.com/HOTR_AttractionMain.htm
http://sanjaal.com/gallery/thumbnails.php?album=9
The selected media item is not currently available.Barry BEAM #16014
2003 U320 40' AGDS
Beamalarm, Foretravel technical help and specifications
"Whatever the mind can conceive and believe, it can achieve"
 

Re: 12volt mystery

Reply #9 –
Regarding your tour of Michigan.  It all depends on the routes you intend to take on your trip.
Email me privately if you like.
jontwork@gmail.com
Regards,
JON TWORK KB8RSA
JON TWORK KB8RSA
Full Time RVer (10+ Years) & Dedicated Boondocker
Retired, Unemployed, Homeless Transients
1996 Foretravel U270-36 w/24' Timberwolf Trailer
I firmly believe that tomorrow holds the possibility for new technologies, astounding discoveries, and a reprieve from my remaining obligations.
Welcome to WeRV2 (Under Construction)
Find Jon: Via Satellite Tracker Datastorm Users
The Second Amendment is in place in case they ignore the others.