Hoping you guys can help me diagnose this before I start ripping wires:

Truck startd blowing the # 8 fuse under the hood tonight (15 amp #8 - trailer tow electronic brake illumination, park lamps, trailer tow park lamp relay coil fuse) which also controls the dash board lights (can't see gauges at night) and the tail light lights (brakes lights work) are out too.

Figure I have a short somewhere.

Thanks in advance

Jed

 

Here's a pic of manual. See #8.

Also a pic of the trailer breaks, which I didn't install nor have I touched since I've had it.

 

Try again on #8

 

Been reading about a fuel bowl heater short but can't find anything that matches to 2001 F250. Only older models and it's a 30 amp fuse

 

The 30 amp fuse has nothing to do with your issue. You have a short some where and need to find it. Have you tried going through the wiring at the trailer harness behind the bumper?

 

My thoughts, check the plug under the back bumper for the trailer connection to see if the wiring didnt get chaffed and causing a short, specially where all the wires go into the metal part.

 

Will start checking today. Wanted and idea on starting point first. I will advise. Since you mentioned that area, the only thing I've done lately to make this start is I reattached the spare tire beneath the bed. The previous owner had it laying in truck bed. Maybe I squeezed something putting it back under there. What's your thoughts on the aftermarket brakes I put in photo? I have no need for them.

Thanks

 

Thanks for help

 

I checked all the wires and harnesses at rear bumper. All look dirty but nothing stands out. I will go back to that but wanted to asked about a couple things to check first:

1. Will a scan program (Forscan or Dash Command) tell me anything?
2. I noticed my door bell is not working but the headlight bell is working.
3. The fuse blows as soon as I turn the light switch to on.
4. Could it be a bad light switch?
5. And could be anything in the steering column?

Thanks again for any suggestions.

Jed

 

A scan program will not help with this particular problem, in fact most fuse problems will not be detectable by a scan program.

The light switch is working properly.

The rear wiring harness leaves the cab under the front left firewall I believe. Check the point where it goes out of the cab for wiring damage. It runs along the left frame and can be unplugged from the rear trailer harness to isolate that harness.

However, the fuse for trailer lights and trailer brakes is normally separate from the truck tail lights. The relays for the trailer brakes and brake lights may be fed from the truck light fuse. It might make sense to remove the brake controller and tape off any bare connections.

I suggest you remove the attachments to the frame rail and closely inspect the harness that connects to the rear lights for a bare wire. Then while the harness is loose, try the light switch to see if the fuse blows.

Another potential spot to look is the bed under the rear lights to see if the wiring has gotten damaged where it goes up to the lights.

A final thing to check for - when a wire is repeatedly overloaded or shorted, the wire and insulation can overheat, causing the insulation to melt, allowing the 12 volt wire to short to a grounded wire in the harness. This is harder to find. Replacement harnesses are available, but you could untape the harness and check each wire to the back for melted insulation.

Good luck,
Larry

 

A scan program will not help with this particular problem, in fact most fuse problems will not be detectable by a scan program.

The light switch is working properly.

The rear wiring harness leaves the cab under the front left firewall I believe. Check the point where it goes out of the cab for wiring damage. It runs along the left frame and can be unplugged from the rear trailer harness to isolate that harness.

However, the fuse for trailer lights and trailer brakes is normally separate from the truck tail lights. The relays for the trailer brakes and brake lights may be fed from the truck light fuse. It might make sense to remove the brake controller and tape off any bare connections.

I suggest you remove the attachments to the frame rail and closely inspect the harness that connects to the rear lights for a bare wire. Then while the harness is loose, try the light switch to see if the fuse blows.

Another potential spot to look is the bed under the rear lights to see if the wiring has gotten damaged where it goes up to the lights.

A final thing to check for - when a wire is repeatedly overloaded or shorted, the wire and insulation can overheat, causing the insulation to melt, allowing the 12 volt wire to short to a grounded wire in the harness. This is harder to find. Replacement harnesses are available, but you could untape the harness and check each wire to the back for melted insulation.

The door chime may have been bypassed by a previous owner, a common modification.

Good luck,
Larry

 

I took out the light switch and check wires. It has two connectors on the back.... A big one and small one for something. To make a long story short, if I leave the small one disconnected, the fuse does not blow. The taillights work now with the small one unplugged. If I plug up small one and turn on parking lights, the fuse blows. My door chime now works if I leave the small connector unplugged.

Questions:

1. what does the small (3 wires I believe) control? Fog lights, cluster dimmer lights??????

2. would it be a switch problem or a short in that 3 wire connector?

3. If it is a wire short problem, where would I start when chasing that 3 wire connector?

Thanks again

 

Well, the fog lights work with the small connector unplugged. So, It appears the 3 wire connector controls only the instrument cluster panel lights. Before I start tracing those wires, do you think it's worth the time or should I just get a new switch?

On another thought: I now remember playing around with that cluster dimmer switch the other day adjusting the cluster lights and turning on the dome light. That's the only time I've ever touched it. Maybe shorted the switch????

Thanks

 

Can't find any wiring issues with the small connector but I didn't really track each wire because I couldn't get to them. The connector looks pretty good. Is there a way to check the switch with a meter before I spend the cash ordering one?

Thanks jed

 

Jed,

As an electrician I can tell you that your switch will not blow the fuse, but if you keep on replacing the fuse, you will eventually need to replace the switch, maybe the whole fuse block and/or the wiring harness.

Troubleshooting vehicle wiring does require some basic electrical and test equipment knowledge. That does not mean you are dumb. I don't know how to fix my computer, so when it f's up, I take it to a guy who knows computers.

I strongly suggest taking your truck in to an vehicle elec. shop preferably, not a dealer. It will be cheaper in the short and long run than throwing unneeded parts at the truck.

If you keep messing around, you will do more damage. Get someone's help who knows electrical troubleshooting.

Best of luck,
Larry