I have a WFCO ULTRA III Distribution center (Fuse Box)This unit has an open circuit lamp on each fuse. When fuse is blown or removed, the lamps light up. Problem: A fuse blew when I was extending the awning. This should have resulted in the lamp to be lit, it wasn't, nor did it light when I removed the blown fuse. Is this due to a fault in the box, or some other condition that would cause both the short and the unlit lamp? Like a loose connection some where in the circuit?

TS21sso wrote:I have a WFCO ULTRA III Distribution center (Fuse Box)This unit has an open circuit lamp on each fuse. When fuse is blown or removed, the lamps light up. Problem: A fuse blew when I was extending the awning. This should have resulted in the lamp to be lit, it wasn't, nor did it light when I removed the blown fuse. Is this due to a fault in the box, or some other condition that would cause both the short and the unlit lamp? Like a loose connection some where in the circuit?Probably nothing wrong with the sense circuit. It's a byproduct of how the circuit works. The lamp won't always light when fuse blows. Why????? Well here is how that circuit works. When the fuse blows, IF the circuit is trying to draw current, a small amount of current will flow through the high resistance sense circuit, causing a transistor to turn on, which then lets current flow through the LED.However, IF the circuit isn't trying to draw power, NO light. So it will work fine on circuits with a light on, radio, tv. etc. It will almost NEVER work on things like awnings, etc. However, IF you were to try to extend or retract the awning, then I'll bet you will see the LED light with the fuse blown. Hope this helps explain that circuit. It is handy, but not foolproof.

Or somebody put a in normal fuse that doesn't have the light in it.

ScottG wrote:Or somebody put a in normal fuse that doesn't have the light in it.light is in the panel not the fuse.

One side of the fuse is +12 volts and the other side is the load. In parallel with the fuse is a resistor and an LED. The fuse normally shorts out the resistor and LEC so there is no voltage across them. If the load shorts or draws so much current the fuse blows, there is now voltage across the resistor/LED and it lights. The awning drew enough to blow the fuse and light the light but then you took you finger off the switch which removed the load. Now there's no voltage across the LED because no current is flowing in the circuit. Hit the button for the awning and you'll see the LED light.

Must be a load on the terminal for the lamp to illuminate.

Open circuit lamp | Good Sam Community

12 Replies

Bobbo
Explorer III
Oct 24, 2013
Thank you for the follow up.
TS21sso
Explorer
Oct 24, 2013
Thanks for all the replies.
While cleaning the track and putting some lubricant on the pivot points of the arms, I found the problem. The wire to the motor is fed through the arms. The wire was pinched with a slight cut in the insulation at the first joint. When pressure was on this joint, it caused a short.
TS21sso
Explorer
Oct 22, 2013
Bobbo wrote:
Does the fuse blow instantly, or does it run a while first?

If it runs a while first, it sounds like the awning motor is drawing too much current. Have you lubed the joints of the awning arms? Too much friction resistance may cause the amp draw to go up.

If it blows instantly, it sounds like you have a short in the wiring.

Thanks for the insight to the possible problem.
The first time it blew the awning was extended about a foot. The second time, it was fully extended. I will lube all the joints and see if the problem is corrected.
Bobbo
Explorer III
Oct 22, 2013
Does the fuse blow instantly, or does it run a while first?

If it runs a while first, it sounds like the awning motor is drawing too much current. Have you lubed the joints of the awning arms? Too much friction resistance may cause the amp draw to go up.

If it blows instantly, it sounds like you have a short in the wiring.
TS21sso
Explorer
Oct 22, 2013
wa8yxm wrote:
One thing about fuses.... Sometimes.. They blow, for no good reason.

This is the second time for this fuse to blow, both times as the awning is being extended.
wa8yxm
Explorer III
Oct 21, 2013
One thing about fuses.... Sometimes.. They blow, for no good reason.
TS21sso
Explorer
Oct 21, 2013
Thanks to both ktmrfs & Roadpilot for giving me a better understand as to how this unit functions. Now to find either the short that caused the fuse to blow or why the awning would draw enough power to blow a 20 amp fuse.
time2roll
Nomad
Oct 21, 2013
Must be a load on the terminal for the lamp to illuminate.
Roadpilot
Explorer
Oct 21, 2013
One side of the fuse is +12 volts and the other side is the load. In parallel with the fuse is a resistor and an LED. The fuse normally shorts out the resistor and LEC so there is no voltage across them. If the load shorts or draws so much current the fuse blows, there is now voltage across the resistor/LED and it lights.

The awning drew enough to blow the fuse and light the light but then you took you finger off the switch which removed the load. Now there's no voltage across the LED because no current is flowing in the circuit. Hit the button for the awning and you'll see the LED light.
ktmrfs
Explorer II
Oct 21, 2013
ScottG wrote:
Or somebody put a in normal fuse that doesn't have the light in it.

light is in the panel not the fuse.