Multifunction Switch (MFS) issue

[ClayAkers]

Not sure what happened, one minute everything was fine, the next a guy pulls up next to me (in a JKU) telling me I don’t have brake lights.

I was on my way home anyway, so I checked and neither the turn signals, flashers, not the brake lights worked, but the tail lights worked.

Turns out the brake light fuse in the glove box and the MFS fuse under the hood were blown. When I replaced the MFS fuse it blew immediately.

Any ideas where I need to start trying to find the problem?

 

[7slotMT]

Not sure what happened, one minute everything was fine, the next a guy pulls up next to me (in a JKU) telling me I don’t have brake lights.

I was on my way home anyway, so I checked and neither the turn signals, flashers, not the brake lights worked, but the tail lights worked.

Turns out the brake light fuse in the glove box and the MFS fuse under the hood were blown. When I replaced the MFS fuse it blew immediately.

Any ideas where I need to start trying to find the problem?

I would start by checking all the common grounds.

 

[LJBean]

I'd first try unhooking the MFS at the steering column and see if the fuse blows again. If it does, then likely it's not the MFS. If it doesn't, then it's either the MFS or on a circuit that's normally closed coming through the MFS.

 

[Jerry Bransford]

Remove borh brake light bulbs and see if the fuse still blows. Check how the bulbs were inserted into their sockets as you remove them, they can get jammed in rotated 180 degrees out and cause the fuse to blow.

 

[dbbd1]

And check the third brake light "buttons" and connections .

 

[ClayAkers]

Thanks for the help everyone! I replaced the MFS relay and all is well.

I just replaced that one about a year ago with one I got from AutoZone. And I had to go back to AZ for this one too.

My wife just told me to order “a good one instead of the one from …” [she pauses searching for the name of the store, then waves her hand in dismissal] “Dollar General for cars”.

Never in my life have I heard a more accurate description of a place.

 

[Jerry Bransford]

Thanks for the help everyone! I replaced the MFS relay and all is well.

I just replaced that one about a year ago with one I got from AutoZone. And I had to go back to AZ for this one too.

I'd stop buying any of Autozone's Duralast parts, they don't hold up. If you can't find a Mopar at least go to NAPA and ask for their best premium replacement, they have a couple levels of quality on many parts.

 

[NskLJ]

I'd stop buying any of Autozone's Duralast parts, they don't hold up. If you can't find a Mopar at least go to NAPA and ask for their best premium replacement, they have a couple levels of quality on many parts.

Very true on the level of quality Jerry, even with known brands I have found quality issues these days. I like to use rock auto for parts that way I can see most brans available and make a decision from there.