1997 F150 4x4

both tail lights out..
both license tag lights out.. one looks to be burned out, the other ok
both turn sigs work..
both brake lights work..
both headlights work..
both flashers work..
both hi/low beams work..

I did check all fuses and they 'look' ok. The bulbs also 'look' OK. Can anyone say exactly which fuse to check? The manual was a bit vague.

Months back I towed a trailer. The trailer lights worked on another vehicle, but on mine, there was some unexpected behavior. As I recall... when I applied the brakes, the trailer's tail light came on, and another one or two strange behaviors.

Any ideas?

 

It sounds like a fuse for the running lights. If all the fuses look ok, there could be something wrong with the lightswitch. If I can find my cd, I will see what fuse it might be.

 

Thanks.. yes.. see what fuse you can find.. either by the driver's left knee or under the hood just behind the air filter. I pulled about every fuse.. at least the 20A and 15A ones. The "looked" ok. I pulled the 'audio' 15 or 20 (I forget which now) one under the hood and swapped it with other like ones. When pulled the 'radio' did not work.. so I know it was good. Thinking I might need to start tracing wires.. uuuugh!

 

If your front running/park lamps are okay, it isn't a fuse.

You probably have a damaged harness or corroded connector pin. Based on your reported problem with that trailer, I'd say you also have a bad ground at the rear of the truck.

Here's the schematic from the CD: 1997 F150 Exterior Lamps.pdf

Let me know if you need more.

Steve

 

Are the grounds leads that bolt onto the frame?

Any idea about where they are?

 

What front running/park lamps are you referring to? I don't think I have any lights on in the front unless I turn on the head lights.

 

The front lights should come on when u pull headlight switch to first notch(parking lights).

 

Hmmm.. You aren't familiar with the concept of parking lights?

 

"The parking light is really not actually used as such in modern driving. This name is more of a throwback to days gone by. When originally named, the parking light was used to illuminate a vehicle when it was parked, because streetlights and special off the road parking areas had not yet become common. Leaving your car parked on the side of a dark road without some warning of its presence was a hazard to both your vehicle, and to other drivers. The parking light was entirely separate from the headlight system. They were not lit when the headlights were turned on as they are in modern vehicles. The purpose of the parking light has changed over the years. Wider roads allowing room for on street parking with no obstruction of the driving lanes have made their original purpose obsolete. The parking light still serves an important function in driving safety, used more as a marker light to make vehicles more visible at night, especially from the side view. Such marker lights became mandatory in 1968, to improve safety and vehicle visibility on the roads. The parking light can also be helpful as backup lighting if you have a headlight burn out during driving. The glow of the parking light can help your vehicle be more visible to oncoming drivers even with only one headlight, making it easier for others to determine that a car, not a motorcycle is approaching. "

 

OK.. so the 2nd notch "P" lights do come on in the front, but not the rear. So looking at that schematic, it seems like either I've lost both rear grounds or a connector is loose somewhere between front and back since the whole RH side of that schematic is "dead", except the 'stop' and 'turn' signals do work (but perhaps there's also an independent circuit for another set of bulbs?) Are those double arrow (>>) looking things connectors? If so, then it seems there's a connector at the front and rear.

 

Parking brake/emergency brake. It's just common terminology.

 

You are on the right track. The >> things are connectors. You can see in the diagram they are labeled "C***". The "C" stands for connector. If you have a testlight or voltmeter, you can find some of these and see if you have voltage on the brown wire with the headlight switch halfway out.

 

Does anyone happen to know where the grounds and connectors are relative to the underbody.. looking for some point of reference.. e.g. fuel filter.. muffler.. etc.

 

Pull the tail lights out of the bed and look inside. Ford grounds the to the body behind the lights. It will have a ground on bothe sides. I would look under the back of the bed at te plug in the wiring harness. If it has an aftermarket adapter for the trailer plug or someone has spliced the wires or used scotch locks to tap the wires they may have broke, came loose or have corroded the plug pins or caused the wires to break.

 

RESOLVED - F150 owners may want to take note of this.

The cause was an eroded wire splice where the harness splits out the rear-end lights from the trailer lights. Three of the 6 wires are spliced with a crimp connector and the brown had corroded and broke. You need to drop the spare tire and on the driver's side in the frame channel you will find the main harness splitting into 3 sets of wires. 1 set is all the rear-end lights. That set about 6" towards the rear has 3 crimp splices (all wrapped in tape.. so you have to uncover) and those crimps appear to be subject to failure. I cut them out, soldered the wires, and wrapped w/ electrical tape.