Running lights fuse keeps blowing

[tny_bubls]

Sent: 7/27/2003

Hey all, my wife and I have just inherited a '77 Minnie Winnie with some issues. Aside from major roof damage (thanks for all the posts on that), it is blowing the 15A fuse for the running lights along the top of the vehicle. I tried removing all the bulbs and putting in a new fuse, but it blows as soon as you turn on the lights. Any clever ideas on where to start? When I pulled the covers to remove the bulbs several were swimming in water, but they've been dry for several days now. It looks like there is a fair bit of corrosion where the screws have rusted over time. Thanks for any info.

John
Chapel Hill, NC

[denisondc]

Sent: 7/27/2003

I presume it has to be a wire shorted to the skin or frame or ground wire somewhere, or a short inside a light assembly itself. Those bulb sockets are pretty easily damaged. This has happened to me, on my Winny and on other old vehicles.
I work on this situation by using an old headlamp, wires attached to it, and connected in series across the blown fuse for the running lights. If there is a short it will light the bulb - and fiddling with the wires at all the different emergence points might allow you to see the headlamp-bulb-test-tool flickering. I have long enough wires to the test-tool so I can have it visible from wherever else on the RV I am working from. When you eliminate the short, the headlamp-bulb-test-tool will get dimmer, if not go dark. Saves burning up so many fuses. Dont discount that it is under the dash either. Good luck and let us know if you find it. denison

[tny_bubls]

Sent: 7/27/2003

Thanks for the advice. Do you know if all the lights are wired in series? Would it be possible to remove one in the middle of the string and thereby isolate the fault to the front or rear of the vehicle? Does that make sense?

[Boat Nut]

Sent: 7/27/2003

Admittedly your 77 may not be like my 73. In which case, your on your own. In mine the running lights are routed under the coach to the rear. They come through the floor in a rear hatch compartment. They are contained in a 4 pin plastic electrical connector. The brown wire is the running lights.

Using Denison's good idea of substituting a 12 volt light bulb for the fuse, disconnect this connector to see if the light (fuse sub) goes out. In mine the wire for the front top clearance lights is routed forward again on the driver side, after a daisy chain with the left top rear clearance light. (kind of a weird arrangement considering the wires first were routed from the front to back down below & now going forward again @ top.)

Besides the 14 top clearance lights you are also trying to light 2 parking lights up front and the 2 tail lights.
Good luck
Chuck

[denisondc]

Sent: 7/27/2003

Im sure all your clearance lights are in parallel, i.e. each must have a 12v feed and a ground connection: But I can believe that one feed wire is used to run to several clearance lights, with a tap-off for each; first one, then the next, and the next, going around the vehicle. Such as all five of the lights across the top front, or all five across the top rear, etc. But taking out one bulb wont affect any others, you would have to interrupt the 12 volt feed line. You might see such a 12 volt wire running from light to light, if you can get inside the wall.
And about the time you get the short fixed, you might have lights going dim or going out because the ground connection between the light housing and the skin is not so good after all the years. One by one I have run ground wires to most of the the lights that I can reach the back of - to add a real ground wire. In Virginia we have an annual safety inspection requirement, and about every year there is another exterior light that I have to coax back to operation before I take it in. I hope my explanation is readable. denison

[Boat Nut]

Sent: 7/28/2003

Hi,
The bulbs are not wired in series, they are in parallel. Although this is confusing to some because the wires seem to run from one socket to the next. You will notice, on close inspection, that the wires into and out of each bulb socket are actually connected together to the same bulb contact. If they were in series, they would each connect to different bulb contacts, so that the current would have to pass through each bulb to get to the next.

This form of connection is sometimes called a daisy chain. If you disconnect the first socket in the chain you will have disconnected all of those beyond it.  However, pulling the bulb doesn't do it. If you disconnect a middle one in the chain, you will effect all those beyond it, but not those before it.

Good luck
Chuck

[james]

Sent: 7/29/2003

John, good info. on your problem. It just takes time to trace out a bad wire.
   Its good to see someone from NC on this site. I live near Benson on I40 exit 334.You are always welcome to take a road trip down and we can swap stories.
I buy sell and work on these rigs mostly as a hobby. Most any Sat. you will find one or two campers at my house with their crews doing PM.
Again Welcome
James Barefoot