marker light fuse keeps blowing

[daffy]

I've had a problem pop up that may be very annoying, hopefully someone has a quick answer for me.

I keep blowing fuse #11 under the hood (book says parklamps relay and Mainlight switch). Which pretty much explains what's going on.

When the fuse blows my tail lights, and front marker lights go out, as well as my dashlights, and I believe my fog lights. My brake lights work fine, and my headlights will come on if I turn the switch on.

I have searched here, and tried replacing the main switch, and swapped the relay with the interior lights relay, no change.

After I replace the fuse, I'm pretty sure all the bulbs work, but I cannot remember if the foglights worked or not. The first time I replace the fuse it lasted 2 days, today it lasted about 10 minutes.

In this part of the world, days are getting short, and "I'm sorry officer, I just picked up a switch to fix it tonight" aint gonna cut it for long.

Anyone had problems with the wireloom shorting in a particular spot?

Anyone else had this problem that fixed it in a different way?

Oh yeah, one more weird thing, when the fuse is blown and I turn on my lights, ALL of my dash indicators go out (cruise, O/D. 4x4, etc), as soon as I turn the switch back off, they return.

Help!

 

[BrooklynBay]

What are you doing right before the fuse blows (stepping on the brake pedal, turning on the cruise control, adjusting the dimmer for the dashboard illumination, etc)?

 

[daffy]

I don't honestly know. It was just dark enough tonight to turn on the auto headlamps, so I didn't notice when the dash went out. Just looked down at a light, and they were out.

Anyone know what all that fuse has running through it?

I know that it doesn't take a 15A fuse to protect a little relay like that.

I was going to start pulling things (non-essential first) until it stopped blowing.

Thanks

 

[budwich]

Try playing with your MFS switch and seeing if that is the cause of the fuse blowing.

 

[daffy]

Thanks for the reply budwich!


nope, no luck there, but I was only testing in the driveway.

We'll have to see how long it lasts in the morning, and whether I can notice when it blows.

 

[budwich]

one thing I don't understand is your last statement of the first post... "Oh yeah, one more weird thing, when the fuse is blown and I turn on my lights, ALL of my dash indicators go out (cruise, O/D. 4x4, etc), as soon as I turn the switch back off, they return." Are you sure its not the other way around???? cause they get their power from fuse 11 and when its blown, I can't see how they can be powered????????

My "new guess" is that your autolamps is the cause of your problem.... try turning it off.... and next one after that is your dimmer relay is fubarred.

 

[daffy]

Do the indicators (i'm not talking the illuminators) get their power from the same source?

I tested by pushing the O/D off, making the yellow indicator light up, when I turn the main switch to the first position (parking lamps) or the second (headlights) the O/D off light goes out.

I was thinking dimmer too, but why would the dimmer be with the exterior lamps?

I really need to get a hold of a schematic, it may make more sense.

 

[rwenzing]

I tested by pushing the O/D off, making the yellow indicator light up, when I turn the main switch to the first position (parking lamps) or the second (headlights) the O/D off light goes out.

This makes perfect sense.

When the headlight switch is in the off position, the I/P indicators are powered directly from dash fuse 11 when the ignition is on. That makes them bright at all times for daytime use.

When the main headlight switch is in park or head (or Autolamps is active), the I/P indicators are powered from underhood fuse 11 by way of the dimmer module. That allows the indicators to be dimmed along with the other dash lamps.

So, if underhood fuse 11 is blown, the indicators have no power source except when the headlight switch is in the off position.

 

[budwich]

ah yes... sorry I didn't see the "interior fuse" designation. One other question, I assume that you are running "standard headlights" and not some sort of "ultra-brights".

 

[chickenviii]

lust a long shot but............ive seen this on f-250's where the wires from the shifter for the od switch rub on the top of the steering column and wear through the insulation causing the fuse for the dash lights to blow sometimes when the veh is put into gear, pull off your column cover off and just look at the 2 small black wires from the shifter, ill see if i can get some diagrams up for ya

 

[chickenviii]

you want diagrams??!! LOL hope this helps

hope this helps

 

[daffy]

WOW! THAT'S FRICKIN' AWESOME!

Hopefully I found the problem tonight.

This morning, I fired it up, and all was working, I backed out of the driveway, and 'click' I heard the lights go out, just as the back tires dropped off the lip of the driveway.

So, tonight I crawl under the back of the truck and see: (it's a bad picture, but I think you'll see)

The trailer wiring harness had rubbed on that bracket, and worn through.

Can't make it out from the picture very well, but the insulation was melted.

I split the harness and taped up the wires.

{crossing fingers} hopefully I won't be replacing any more $.75 fuses, or $40 switches.

 

[chickenviii]

good chance

 

[daffy]

Well, a full day has passed, I think that was it.

Thanks to all who suggested stuff!

 

[BrooklynBay]

Thanks for the update!