Hey all. Not sure where to put this, so if a Mod needs so slap me around for cross-posting in electrical, I apologize!

Like so many around here, I am introducing myself and my truck by way of my problem. Got a '99 F250 SD XLT 4x4, 7.3 PSD, Extended Cab, SWB.

I've had a series of electrical problems mainly involving the turn signals, parking lights, and hazards. I replaced the flasher and a few relays, fixed some bad grounds, and replaced bad fuses, and have arrived at one problem I can't seem to fix.

The most recent problem was that the parking lights and the dimmer light on the instrument panel would stay on even after all switches and the truck were turned off. I could get them to turn off by pulling the relay for the trailer tow park lamp/brake illumination. I could also pull fuse # 8 in the power distribution box under the hood and get them to go out. This fuse is for "trailer tow electronic brake illumination, park lamps, and trailer tow park lamp relay coil"

I looked at the two wiring harnesses and connectors above the spare tire, for the tail lights and trailer hookup, and found the remnant wires of some aftermarket crap that had been spliced in there. It is also almost certain that the previous owner submerged the trailer hookup launching a boat, if that makes any difference.

Cleaned everything up, redid the grounds for both harnesses, and now my parking lights turn on and off as they should, but the dimmer light in the instrument panel still stays on unless I pull fuse #8, mentioned above, or unplug the headlight switch. No other fuses affect it. I've blown this fuse several times, usually by accidentally creating a short to ground with a test light or moving wires.

Poking around under the dash, I've noticed that some of the wiring is messy. There are a bunch of ground wires spliced together from different harnesses, switches, etc. They all attach to a good ground (as far as I can tell) but I don't know if this would allow my instrument panel light to find its ground through some other circuit (like parking lights or trailer tow lights).

At one point in all of this my brake lights stopped working (turned out to be blown fuse #13 for the stop lamps, CHMSL, and trailer tow stop lamp). When I checked out my brake switch I found two hot wires going to it when there's only supposed to be one. The one that's not supposed to be hot runs into the back of the fuse panel.

Interestingly, I found another wire from the brake switch ran into a very weird splice. It included:

• this wire from the brake light switch, which was not hot
• three very thin wires (22 guage) that ran into a harness in the firewall (none of these were hot)
• one wire that came down from the instrument panel, that was hot when the dimmer light stayed on
• A large ground wire
• A wire that ran into the back of the fuse panel

I thought it was very strange that these wires would all just be mashed together and covered in heat shrink...especially with a ground wire that wasn't part of a harness, switch, relay or anything. I disconnected the battery, cut the ground wire, reconnected everything, and the dimmer light was still on. Touched the ground wire back together and blew fuse 8 again.

Also, now when I turn the ignition on without starting the truck, I get a nasty clicking/grinding sound out of my flasher relay. That's where I left off when I had to stop working on it for the day.

Based on everything I've read, it seems like it could be:

-(edited to add) Messed up wiring causing a 12V feed into the parking light circuit

-Short to ground somewhere in the circuit with fuse 8 (park lamps, trailer tow brake lights, trailer tow park lamp relay), which could include the plugs back by the tail lights.

-Bad headlight switch

-Bad multi-function switch

Any ideas? advice? Thanks in advance.

 

Welcome to FTE!

Your post is fine where it is. One of the electrical gurus will be in shortly to help you out.

 

Bump! He took a long time to type that out. He deserves help lol

 

Thanks Spooner, and nice ride! I was thinking about flying a flag on mine, if I can get it to stop acting like a POS.

 

sounds like problem is your multifunction switch, i would start there, was a common problem with fords

 

You can test the headlight switch but my money is on a short in the system. If it wasn't a short you wouldn't keep blowing fuse 8 by moving wires

 

I'm with you. My headlight switch and my MFS switch could both be on the fritz, especially if a short in the system pulled too much amperage through either of them. Even when they're both unplugged the brown wire for the parking lights/marker lights circuit is "hot" which it shouldn't be unless the headlight switch is plugged in and turned on. It's getting a feed from somewhere it shouldn't be.

Anyone have any real advice for tracking that down, besides just going through all of the brown wires inch by inch trying to find the feed? There's a lot of brown wire in very hard to reach places on the truck.

 

Do continuity tests on the switches. The only way i know to diagnose wire issues like is to trace that system on a wiring schematic and trace each individual wire.