I apologize for repeating a thread but couldn't find it with the search.
A few days ago someone posted about a blown 5 amp fuse (number 27) on the fog lamp circuit after having done the fog lamp switch modification and wiring splice. I too have noticed this fuse is blown. I didn't see an answer to whether or not this was significant. All you electrical gurus out there - any thoughts?

 

I have fog lights on my Lariat 4x4, I will check the fuse size and get back with you.

A 5 amp fuse sounds a little small to me but I could be wrong. If 5 amps is right then that makes max current for both lights to be 5 amps. Two lights running on 5 amps at 12 volts is 60 watts total, or 30 watts each. I am guessing but I would think that 30 watts for a fog lamp would be pretty whimpy. I would guess more like 80 watts each which makes 160 watts total which would require a 15 amp fuse. I don't understand exactly understand the switch modification you did. Maybe you can expand on that and Maybe I could be of more help.

If you know the bulb wattage then I can recommend a fuse real easy and won't have to guess.

I will check mine tomorrow and quit guessing. Either way, sounds like the fuse is too small if it blows.

DaveMan

 

The wiring diagrams show the 5 Amp fuse in line with the fog lamp relay. The switched 12V is fused at 15 Amps.

 

Hey F150Forever,

That makes a little more sense now that I understand that there is a relay involved. Either way, almost any time there is a fuse blowing on the power side of a relay there must be a serious mis-wiring problem.

The wiring feeding the relay should be checked cause sounds like the relay coil may need some sort suppression to help reduce spikes caused when the lights are turned off. Relay coil suppression is required in almost every application using relays and is commonly done by connecting a diode accross the relay coil circuit. If suppression is included a relay installation, and it is installed backwards, then the relay coil becomes a direct short for the fused circuit feeding the coil and bamm, the fuse will blow as soon as power is connected.

In my experience, most 12V relays draw less than one amp to power the coil, after all, that's the main reason to use a relay in the first place, to create an electrical switch of a higher amp circuit with a lower one.

My $0.02

DaveMan

 

I had the same problem after the doing the fog light mod. I only did the electrical portion, so I could have fogs and brights. My problem was that the connectors that I used to splice the two wires together were not tight enough. The poor conection caused it to draw too many amps and blew the fuse. I tightened the connectors and have not had the problem since.

 

Silver Sport,

To make sure that doesn't happen in the future, try soldering all your splice connections, it takes a little more time but you'll never regret soldering a connection, as you will, sooner or later with a crimped one.

Ed

 

I did the same mod a few months ago. I had the same fuse blow several times. I came back to the board and asked why. Someone replied and after tightening the spliced connection I didn't have any more blown fuses. Been going strong without a hitch ever since. The first few times I changed the fuse, it blew during the change. I finally dosconnected the battery cable and made all my repairs without the wires being hot. It seemed to help.

 

Hey Guys

You dont need the fuse.
The splice causes the parking lights to feed the
fog lights.
With my 2001 Supercrew, I installed the fog light
kit and DRLs.
I pulled fuse #27 and modified a "Scotch lock"
splice to accept 2 wires in line. Splicing the brown and
White/Black wires together.

Now in auto headlamp mode with the fog switch pulled
the fog lights are off, when the sun sets, my lights
go on full mode along with my fogs.
With the fog switch pulled out my fogs stay on with
high beams too!!!

See attached

Pat