#18 fuse is blowing when I hit the brakes....no brake lights.

[ToMang07]

Ok, so got home tonight, and went to back up the driveway and noticed I had no brake lights. Running lights are working fine. Checked the manual...and sure enough the #18 fuse is blown. I replace it, and the soon as I hit the brakes, the brakes light up for a millisecond, and the fuse pops again.

Help.... I absolutely SUCK with electrical issues.....I already looked under the dash and couldn't find anything abnormal. Really need some help/troubleshooting assistance.

Thanks in advance, fellas.

From the Manual:

#18 (20A*) Turn lamps/Brake on-off switch (high)

 

[ToMang07]

I should add the 3rd brake does not work, blinkers do not work, (front or rear) dash-turn indicators do not work, and 4-ways do not work.

FML.

 

[TyCorr]

#18? Isn't that the fuel bowl heater circuit? If so, there's your help.

 

[ToMang07]

#18? Isn't that the fuel bowl heater circuit? If so, there's your help.

No, it's the brakes and turn signals. Per the manual:

#18 (20A*) Turn lamps/Brake on-off switch (high)

 

[Arisley]

Look for a wire shorting to ground. Probably back by the brake lights.

 

[mudwizer]

see if you backed in your trailer plug

 

[ToMang07]

Look for a wire shorting to ground. Probably back by the brake lights.

Spent a LOT of time doing that. Found nothing but rust and grime.

see if you backed in your trailer plug

Nothing there, and I haven't since I owned the truck.

Update:

I think it is fixed. I got a tip on another forum to check the relay under the hood on the driver's fender and switch the 2. (Electronic Wiring Manual says one is for A/C, the other is for "Flasher Relay" which does not appear in the normal manual.)

Switched them...brake lights/blinkers work again, and no popped fuse! Woot!

 

[TARM]

Now you need to go and pick up the proper relay so your AC works when you need it.

 

[TrailerHauler]

That's strange. I would've guessed a short to ground around the back of the truck.

 

[Powerstrokeracing]

Next thing I would do is getting a wiring diagram and test for resistance in the wires..

 

[PatriotHauling]

Next thing I would do is getting a wiring diagram and test for resistance in the wires..

Lol he doesnt know how to do that. ointlaugh:
He HATES electrical problems.

 

[Arisley]

Wow. Relays fail in the strangest ways. I always have a couple of spare relays in my truck. At the age these things are getting, you never know when one is going to die.

 

[ToMang07]

Lol he doesnt know how to do that. ointlaugh:
He HATES electrical problems.

^Yup. :flush:

 

[JLDickmon]

I'd say maybe a shorted brake light switch.. I don't have diagrams for an 02, maybe I can find online..

try this link
Michigan Electronic Library

use login M123456789012

 

[ToMang07]

I'd say maybe a shorted brake light switch.. I don't have diagrams for an 02, maybe I can find online..

try this link
Michigan Electronic Library

use login M123456789012

I figured it out...it was a relay. (See post #7) Thanks for the link, anyway. :toast:

Also, there is a link under the tech files with a PDF that has the electrons diagrams (ALL of them) for an 02 250/350/EX. VERY useful, only thing I wish it did better was show a diagram of WHERE on the truck the relays/fuses are.

 

[JLDickmon]

I figured it out...it was a relay. (See post #7) Thanks for the link, anyway. :toast:

Also, there is a link under the tech files with a PDF that has the electrons diagrams (ALL of them) for an 02 250/350/EX. VERY useful, only thing I wish it did better was show a diagram of WHERE on the truck the relays/fuses are.

It's called a "component locator" and there's one in the link I provided..

 

[ToMang07]

It's called a "component locator" and there's one in the link I provided..

I see/understand that. I was merely commenting on the on I used, which did not have a locator.

And again, thanks for the link!:thumbup:

 

[viper59]

Same problem trail work fine on 2 other ford trucks keeps blowing fuse #18 .

 

[lightning95]

Same problem trail work fine on 2 other ford trucks keeps blowing fuse #18 .

Mine ended up being the brake pedal switch in cab under the dash. It takes all of 5 minutes to change.

 

[cranstol]

My fuse#18 issue

Thank you all above for the input and things you found. I thought it would be appropriate to share my experience tracking this down on my 2003 Excursion.

Every single time I touched the brakes... *POW*, #18 blew. Started looking for obvious stuff, but nothing.

Disconnected trailer plug etc. via the connector behind the license plate. Tested *POW*

Moved up to the mid-frame area on the drivers side. Disconnected the back end lights from there. *POW* Good thing I have a 20 pack of 20 AMP fuses.

Disconnected those same cables from under the hood right in front of the firewall. *POW*

Disconnected the brake switch. Did not blow, but no brake lights of course. Manually jumped pin 4 and 5 of the brake switch connector. Found a schematic online and those are the contacts bridged by the switch on the 20 amp circuit. *POW* on the manual jumper. Something elsewhere...

Pulled all the relays, etc from the two block areas under the hood just in front of the driver. *POW* The issue is getting in a smaller and smaller area.

Pulled the entire fuse block / power distribution block lose under the dash. 4 bolts 10mm heads. Got a good look behind. Saw nothing. Ready to give up. Tried one last fuse (still have 10 or so left)... maybe it was MY last fuse. Tried the brake, no blow! What?!?

Added relays, etc. back. Tested. *No blow*

Added connectors under hood. *No blow*

Added mid frame connectors. *No blow*

Added connector behind license plate *No blow*

Mounted fuse block / PDB *No blow*

Everything is back together and working. Driven 150+ miles since and it is still working. Not the outcome I exactly wanted as I wonder when (not if) it will pop up again. Hopefully the extra details of the things I did will help someone else down the line with diagnostics.

2003 Excursion 6.0L Limited
2000 Excursion 7.3L Limited
1971 Suburban dead 350 :-(