Hello! I picked a 1986 f150 for $400 that runs actually pretty well and seems to have a lot of clutch life left. It needs a ton of work like most trucks from the 80s but one issue I'm having a hard time with, is the turn signals/ brake lights. They are all over the place. At first, they would not flash and just stay on solid. Replaced the flasher and now the front ones work great but the rear ones are where it gets weird and I'll try to explain it the best I can. The driver one blinks fine until you turn the lights on and then it stops working. Also on the driver side one, the brake light works until the lights are turned on then nothing. On the passenger side, the blinker will work with lights on or off but only if you push the switch up slightly. Once the turn signal lever 'clicks' into place, it turns off. The brake light on this one does work with the lights on or off. I'm at quite a loss and assume it's either the switch behind the steering wheel or my wiring is totally messed up. Thanks for any help.

 

I just went through problems with my turn sig switch on my F-250.
Left turn, had to slightly bump up the lever to get it to flash.

Then one day I could not get the lever to click into the right turn.
Something was jamed up inside keeping the lever from moving.

Pulled the steering wheel, and there was a piece of broken off plastic
laying at the bottom of the switch. At the top of the switch is a springy
piece of plastic, and it broke off. Also there is a plastic ring around the
steering shaft wit a small metal pin which was in the hole, but the plastic
hole was broke and pin leaning over.

Also the 3 phillip screws were all loose.
On the right side are some copper contact strips. Moving the lever up or
down will expose more of the copper. I used a Q Tip and some Dialectrical
grease, and worked it in and scrubbed the strips. Lever move a lot smoother
and the dash green arrows are a lot brighter now.

Got it back together and it all works, except do not have the cancel when
turning.

Some of your light problems could be a ground problem. Clean up the ground
connections and or make sure they are tight. make sure the light sockets are
good and clean w/o corrosion.

I also fixed my 4 way flashers while I was digging around the fuse panel.
They have not worked the almost 5 years I`ve had this thing. Now I have
been under that dash many times. All of a sudden I notice a flasher behind
the panel facing the firewall. It is right behind the flasher you see facing you.

Had to remove the 2 screws holding in the fuse panel and pull it down some.
The male spades were rusted into the female sockets. Had a dickens of a time
getting it out. Replaced it with a PNP one (Good old PNP auto parts) put on
some Dialectrical grease and worked it in and out. Whadayano? 4 ways work.

Next day, no workie. I tweaked the female pins digging out the rusty flasher.
Bent the pins back some and work great now.

Charlie

 

If you have to jiggle the switch, that would indicate a physical problem with it. I’d replace the switch and go from there. Might still be other problems, but fix the known problems first and then see what happens.

 

1980/83 F100/350 & Bronco: TWO different T/S switches. With or without tilt wheel is the difference.

1978/91 F100/350, Bronco & Econoline: Tilt wheel operated by pushing the T/S handle forward.

 

Thanks guys! I’ll order the cam and the switch and see what that does. The hazards work but only in the front but I think that flasher is probably okay since it does engage

 

I think wile waiting for the switch to come I would check / clean all light sockets and grounds.
When lights work till you turn on a different light that is a ground issue.
Dave - - - -

 

Well dumb question... where are the grounds? I’ll also pick up a stoplight switch today and see if that does anything. If not, I’m only out $13 and new parts never hurt

 

Another dumb question... any ideas on how to clean the sockets? They are full of old grease. Bulbs are new

 

Best to get new sockets. The ground wire is the black wire, 90% of the time it is a socket problem, the brass part of the bulb is not making good contact with the small tab on the rim of the socket. It can also be a grounding problem with the cab, you can see on page 6 in this link

Grounds - Gary's Garagemahal (the Bullnose bible)

The rear lighting ground runs all the way up front to a splice behind the dash, and then to a ground G701. If you look at page 11 in the same link, you will see that ground is located up high behind the dash behind the radio area.

You also need to make sure the cab is properly grounded, there should be a ground from the firewall to the engine block.

 

I see! So just splice on new sockets? And I noticed there is a ground on the floor kinda by the drivers side of the bench seat, not sure if that’s a light ground though. Thanks for the links!

 

Um, actually, new parts can hurt. For example, I once dropped a new brake disc on my foot. Hurt like crazy!

Or maybe that wasn't what you meant. But I see zero need to replace your brake switch. You've already noted that one side responds to actuating the brake pedal. That means the brake pedal switch is operating properly. From there, the signal splits side to side within the turn signal switch. Back to my previous suggestion, fix the obvious problem (having to jiggle the turn signal switch) before driving into the weeds elsewhere. Can a new brake pedal switch create new problems? Darn tooting, lots of possibilities there. Maybe you don't get the connector fully seated. Maybe the new switch is bad from stock. Who knows, but I'd highly suggest leaving it alone since we already know it works. Don't load parts in catapult, hoping for a fix. Troubleshoot and figure out what's wrong, versus lobbing parts. Do you need my address for where to send the $13 this will save? Should we include a little extra for the labor I've saved you?

Now, I have to respectfully disagree with esteemed Dave's suggestion to replace the bulb sockets. There's just too much chance of creating new problems, such as mis-wiring one. Talk about a troubleshooting nightmare if that were to happen. Here's how I would proceed. I like your idea to replace any of the bulbs that are acting up. With dual filament bulbs, it's possible for one filament to break loose at one end, and then weld itself to the other filament. This will cause all sorts of strange symptoms.

Instead of replacing the sockets, I would give them a good cleaning for now. Use a plastic-safe aerosol electronic cleaner to get the hardened grease out of there. Don't use brake cleaner, it can damage plastic and wire insulation. Then use a small bristle brush, the kind used for cleaning test tubes, etc. I have a set of brushes that I think were originally meant for cleaning guns. The kit has various sizes, and works great for cleaning bulb sockets. Carefully inspect the socket and if you don't see any corrosion, especially where the pins grab the outer shell, you're generally good. Reapply some fresh dielectric grease, the kind used on spark plug wires. Any parts store will have some. This is an important step that helps prevent corrosion in the future.

With a new turn signal switch installed, new bulbs, and spiffy clean sockets, give your lights another try. If good, you're done. If not, see if the symptoms have changed and continue troubleshooting.

I'd start with the bulb grounds. All of the rear lights are routed to a common ground G701 under the dash. Exactly where it is, I couldn't tell you the location of this mythical terminal. But there's an easy way to make sure it is properly grounded. The cigarette lighter shares this same ground connection. Just in case G701 is not making a good connection to the cab structure, or the cab itself is not properly grounded, run a long test jumper from the outer shell of the lighter socket to the battery's (-) terminal. A long piece of wire with alligator clips at both ends will do the trick.

Another thing you can do is park somewhere dark, away from street lights, porch lights, UFOs, discos, etc. After sunset, have a helper try the lights again. If you've got a problem ground at one socket, you may see other lights illuminate dimly. You have to do this in the dark to be able to see it.

One last trick is to remove the two flashers for the turn signals and 4-way hazards. The one facing the firewall, on the hidden side of the fuse panel, is for the 4-ways. Replace each flasher with a short jumper between the two sockets. You could even use a straightened paper clip, doesn't need to be fancy. The 4-way flasher is hard to access, but if you unbolt the fuse panel from the firewall (2 bolts?), you will have good access. Now you're dealing with a simple on/off circuit, not a flashing one, which makes troubleshooting a LOT easier.

 

I want to say that is for the inside cab light. It has been a wile since I took my truck apart, cab off frame rebuild, but I think that is what it is for.
Could also be for the seat belt? Again been a wile since I took it apart.

I would check the grounds in the engine bay area as a start. As said there should be one from the motor to the cab. You did not say what motor but on my 81 with a 300 six it is on the left side (sitting in the truck) to the firewall. My truck also has one from battery to the frame by the motor mount bracket and then goes to 1 of the starter bolts.
Also in the engine bay there is a bunch of ground wires on the firewall close to the motor to firewall wire.
At each front corner there are also grounds for the side marker / turn lights / head lights.
They keep saying there is a bunch of ground wires inside behind the radio to the firewall but I don't remember them, keep meaning to check one day.

I think I would hold off on replacing the sockets till I checked the grounds and did some testing with a test light.
If you follow the harness out of the cab by the brake master, it goes down to a large plug that is where the rear harness plugs in.
If you follow this back to the tail lights there is another plug for the tail light harness.
Maybe pull apart this plug at the tail light harness and check with a test light to see what you get.
Test light to a good ground if you don't get the test light to do what it is to do then you know you have to move up front to do some more checking.
Dave ----

 

I forgot one more thing. Physically inspect the wiring harness from the tail lights going forward. Look for any splices along the way, typically from somebody adding a trailer plug. A bad job here can cause the tail lights to misbehave.

 

The engine is from a 1979 f150 5.0. Not sure why but it is :-) and actually did notice the rear passenger light is dimmer than the rear drivers light when the lights are on

 

I have had the sockets go bad internally and had to buy new ones. That is why I suggested it.