Hi All -

I'm new to the forum, and new to owning a Ford truck. I recently bought a 1986 Ford F250, primarily for trips to Lowes, the mulch yard, and the like.

At any rate, it can't pass inspection yet because it has some lighting issues. The following lights are not working: Reverse/Back up lights, tag lights, hazard lights (the turn signals work independently, but not when using the hazard switch), and cluster/warning lights on the dash. The weird part about the dash lights is that the Emissions light does come on when I start the truck, but nothing else.

I guess my question is this: is it very likely that these issues are all stemming from one problem, or do I need to start trying to diagnose each problem independently?

I think I have read just about every thread in the forum that pertains to similar issues, but I'm not really sure where to start given the many different responses. I've replaced bulbs and fuses, and replaced the headlight switch as well, all to no avail.

I should also note that I am not very mechanically savvy, but I'm trying to learn (both to save money and because I'm tired of not knowing how to do this stuff), so with all of that in mind, I'd sure appreciate any advice/suggestions on where to start looking for problems.

Thanks all!

 

Hey buddy, welcome aboard! I say you found quite a place. And these trucks aren't too bad to work on. Get a good tool set, sign up here, and you can have her fixed up in a week.

I actually just got my first ford, for the same reasons, an 86 f250 too haha. None of my dash lights worked. Only emissions. I went to a junk yard and pulled a full set of bulbs. The gauge lights, blinkers, warning lights were ALL busted. Not sure how haha.

As for the back- I'd suspect that you have some wiring issues in the back that are causing all of those not to work. You can see the harness this way: lay on your back under the truck. On the inside of the driver's side frame rail you'll see the harness run toward the back, split for the driver's tail light, branch to the plate lights, and then to the passenger side. Do your brake lights work?

You don't mention the transmission but - especially if it's automatic- try wiggling the gear lever while it's in the R position and see if the lights come on.

Don't feel too bad, for inspection I needed lights, belts, smog pump, parking brake, rear view, wipers. Oh, and it didn't run haha.

 

I'm no electrical whiz, but I have gotten a few lights to start working on my truck this week, so I'll weigh in...

I doubt they're all one problem, but some of them are almost certainly related. All the stuff at the back end could well be related. This thread (see here) has some wiring diagrams that someone was kind enough to post to help me through my reverse light issues. In the end the problem was the sockets (don't overlook these) in the back, but you can look at the wiring diagrams to see how everything in the back hooks together.

The instrument light issues could all be related...I don't know anything about the emissions light (given that my 1980 has no such thing), but you could have a bunch of bulbs out, or a bad electrical connector in the instrument cluster. Taking the cluster out isn't that tough of a job, if you haven't done it already to replace the bulbs.

I also had the same problem with my hazard lights...turns out that removing, cleaning, and replacing the flasher unit solved that for me.

I realize I didn't give you much in the way of answers there, so I'll just say this: take it one step at a time. Pick one light (the backup lights are easy, and a good place to start) and test carefully and thoroughly until you find the issue. Wash, rinse, and repeat until they're all working.

 

Welcome to FTE.

I'm surprised I haven't added this to the Sticky, but HERE is a thread telling you everything you ever wanted to know about what makes the Emissions light come on.

The tag lights are on the same circuit as the parking, tail, side marker, overhead roof lights - a single brown wire that feeds all of those. I'd first suspect burned-out bulbs, then begin tracing back from there. PO-added trailer wiring kits are responsible for a lot of lights not working in the back.

I'm confused about your turn signals/emergency flasher description ("the turn signals work independently, but not when using the hazard switch"), I don't believe the turn signals are supposed to work when the emergency flashers are on so I think I'm confused there.

The reverse/backup lights, yeah, go look at that thread Dorsai showed you.

Warning lights on the dash, um.... do you have idiot lights or gauges? I guess I'm wondering which warning lights... the ones on the very top row? Or, others next to the gas & whatever other gauge they give you when you have idiot lights?

Best case scenario, it's the lights at the top of the bezel. You can just remove the bezel (need to first remove headlight & wiper *****, I think there's stuff in the sticky about those) and you can get to them from the front. Hopefully it's just burned-out bulbs, otherwise more diagnostic work is needed. We'll need to know exactly which lamps are not lighting.

You are going to need a Multimeter (if you don't have one, procure one) and, optionally, sometimes a test light is helpful.

 

Thanks, all. I should have been clearer/more specific about some things.

First - Dave804, yes my brake lights work. It's an automatic transmission. I replaced just a few of the light bulbs in the dash, but that didn't fix the problem. Glad to hear I'm not the only one trying to figure this out with relatively little experience.


Second - Dorsai - Thanks for all the pointers.

Ctubutis and any one else: My truck does have trailer lights and brakes that somebody else added right after they bought the truck when it was brand new. The previous owner said the lights were working for him (of course, he could be mistaken), so I guess my thought would be would trailer lights/brakes have caused a problem this long after they were initially installed? there haven't been any changes to them. in at least 2 years as the owner previous to me only had the truck for 2 years, and I've had it for a week. Neither of us made any changes.

Sorry if I was unclear in my hazard lights statement. What i mean is the turn signals work, but the hazard lights don't. That would seem to suggest an issue with the hazard switch on the steering column, wouldn't it?

I have no dash lights where the fuel gage, speedometer, etc. is OR that top row of lights (Emissions - Left turn signal - high beams - brake - right turn signal - 4x4 indicator). The emissions light isn't stuck on or anything, it just lights up when you first turn the ignition (like all of the lights should, I think) and then goes off like it is supposed to. I just thought it was weird that ONE light was functioning, but not the rest. I have replaced those bulbs, like I said, with no luck.

I guess I'll be purchasing a multimeter and getting my first taste of auto wiring work!

Thanks again everybody. Any other ideas are welcome

 

The Fasten Seat Belt light (somewhere in the middle of the top row, I believe just right of the BRAKE lamp) & buzzer come on for ~5 seconds when the key is turned to RUN, the BRAKE light comes on with they key in START as a way to test the bulb. Go read that thread about the Emissions light, it comes on once every ~50,000 miles as a reminder to perform scheduled maintenance.

Poorly-done wiring connections will be exposed to the elements and will corrode over time and eventually fail. This may not be your backup lights/license plate light problem but it very well could be, you will need to investigate your own installation.

Emergency flashers don't work, I would first investigate the flasher and its connections. This flasher is located in the rear side of the fuse panel, directly behind the turn signal flasher. I would clean the connections, look for obvious wiring flaws, probably then swap the flasher for a known-working one.

 

With that many lighting issues, I would be checking all the grounds. Then go from there.

 

+1 on pulling the fuses and checking them. Also, a search herd turned up a fuse box diagram for me. I had several that were the wrong size!

Did the previous owners leave a trailer connected at all times?

 

OK kids, here's where I stand now. Worse shape than before...

Sure enough, I crawled under the back end and there were wire nuts and disconnected wires hanging all over the place on the harness going to the trailer outlet/plug in. (Hmm...Why don't the tag lights work? Well, could be because they aren't connected to anything...)

On one of the wires hanging out of the trailer harness there were several legs wire-nutted to it, but they were not connected to anything, so I removed them. Mistake. Now, for some reason, I have no turn signals.

There was a wire that was hanging loose - no wire nut or anything, just exposed - that was hanging there hot. It was black with a pinkish stripe on it. Coming out of the connections for the back up lights there was a black wire with a pinkish strip on it that was not connected to anything. Suspecting this might be a resolution, I connected the wires. The good news is, it got power to the lights! The bad news is that rather than coming on when I put the truck in reverse, the reverse light now only comes on when I turn the headlights on.

So now I am not sure where to go... any suggestions on how to fix these two new developments?

 

Sounds like you found the wire for the rear running lights. There should be a wire that receives power when the brake switch is activated. Lights dying when you disconnected dead ends sounds like you disturbed a bad connection further up stream.

 

I have the factory wiring diagrams for 82. Not sure if they are the same for 86 as far as the lights.

brown - marker lights
black/pink - reverse
light green/orange - left turn
orange/light blue - right turn
black - ground

Fuse 5 supplies turn and backup lights.
Fuse 1 supplies stop and the hazard flasher.

I would clean all the wires, match up the colors, wire nut for now, and then see what it does. If it works, then make permanent connections. Sounds like some crossed wires still.

 

Stangrc1- the colors you describe seem right for my truck too. I also have two black wires going into each of the four rear light sockets. Any idea what those are for?

Everyone else - thanks again for all of the pointers. I think I got a good start today in terms of at least sorting things out. Probably won't have time to work on it again until next weekend.

Couple of things I think I've found. First, I think I've solved the tag light issue, I just need to get some new little tag lights, as the wires are basically down to stubs stick out the back. They're not connected, but I think I've identified the power source. Will follow up once I've procured the goods...

The trailer wire harness has lots of nasty stuff going on. There are three plugs/harnesses providing power to the trailer plug (is that normal? My dad assures me that on his truck it's just a T connector that the trailer harness taps into; that is definitely not the case on mine. Then again his truck is an '05). One of the plugs/adaptors is broken. When I unplugged it the yellow wire completely fell out/off.

At any rate I'm not sure where to head next. Try to fix the trailer harness adaptors and plug them back in? Might that fix the problem? I'm not familiar enough with the way things are supposed to be back there to tell if this is a bad hack job, or if this is how it's supposed to look. Maybe it's time to take it to an expert...

-Jeff

 

Take it to an expert? Won't fly around here

But in all seriousness, you've already shown you're willing to do work, and can see colors. That's about all you need for working on wiring. Are the connectors those large sort of round ones that have pull tabs on the male side? I have a couple of those back there. Seems stock.

I also have no trailer harness hooked up that I can find. I'll get pictures of the underside of my truck for you tomorrow AM. It sounds like whoever put this wire harness in did so with a weed eater and a lot of hope. Once you figure out what to remove you'll be on the downhill slope. And for the record, yes, there are companies that make T-connectors for our trucks. Plugs in the middle of one of the harness connectors, then has a connection off to the side for a trailer.

I haven't been under my truck much, but I think I remember that the plate lights get power from the running light line to the passenger side of the body, and ground right there. Like I said, I'll get some pictures.

Don't give up just yet. You made some good progress for day one. And as far as we know didn't cut up your hands or throw a fit . Like I did the first time I dealt with wiring haha.

 

Thanks for the encouragement, Dave! I appreciate it. I'm not quite ready to give up just yet.

Nope, didn't cut up my hands too bad, or through any fits (but it came close a couple of times. I don't have a garage or anything, so laying in the gravel in the ally is my workshop).

I appreciate the offer of the pictures. It'll be helpful for me to see what it's suppose to look like.

I'm thinking that now that I've pulled a lot of the junk out of the way, the reverse light problems might go back to the plug at the neutral safety switch. I've read on a couple of other threads in the forum this can cause problems. Might be worth checking out after I look at your pictures.

It won't solve my other rear light issues, like the lack of turn signals, but that might be another place to check when I get back at it later in the week or over the weekend.

jeff

 

My personal feelings are to remove the PO-added trailer wiring and return it to stock.

If you want trailer wiring, go purchase a credible harness that goes inline in your existing harness, it will fit in between two existing Ford connectors.

Like this:



I got one at Amazon:




This should help you with your wiring; it's from my 1981 book but this stuff I believe remained untouched: