Over the past month, the instrument cluster lights in my '86 F-150 302 EFI have been getting dimmer and have finally gone out completely. This morning I was stopped by a police officer because I had no tail lights. The head lights work (low beam and high beam), the turn signals work (front and back), the interior lights work, the cargo light works, and the brake lights work. I checked the fuse for the tail lights and it is good. My Haynes manual makes reference to a fusible link (engine compartment) for the tail lights but I was not able to locate the tail light fusible link in the engine compartment. It appears from the diagram of the headlight switch in the Haynes manual that there are several circuits within the headlight switch - could one of them be bad and causing the no tail light problem? Sorry if this description is sub-optimal but I am a newbie with electrical issues. Any helpful suggestions are appreciated.

Edit: The back-up lights and emergency flashers (front and back), also work - sorry this was omitted in my original post.

2nd Edit: The parking lamps (front / back) and marker lights on the front fenders do not work.

 

I don't think it has anything to do with the fusible link under the hood,those rarely fail in my experience, I drive dirt road for about 200 miles every week with my 98 5.4 and I've seen a lot of crap go bad from use.
I have had fuses that have shaken loose, just loose enough to make you think the worst and look for everything but the simple because fuses don't pop out,ya right. I've also had under brush catch the wiring along side the frame rail and cause it to ground out select lights. So if I were you I'd first be looking at my fuses in the box under hood and cab. Then if that didn't fix it I'd start following the wiring from where it connects to the light itself and on cause that's where your problem will lye

 

Replaced the headlamp switch but the symptoms are exactly the same.
Where are the fuses "in the box under hood"? All we can find is the fuse panel to the left of the driver's column in the cab. Thank you.

 

Sorry, didn't notice the year of the truck.the older fords if I'm not mistaken only have the box in the cab under the dash, go through the fuses one by one, pull them out and put them back in. Then pick a light . thats not working and examine it from th light back to the fuse box until you find the break.the light has a bad connection and is causing other lights on the circuit not to work. Once water got in the brake light in the center of the truck from a bad seal which in turn corroded the wires inside the light which cut current to a few other lights.sometime when your checking wiring as well, the wire get burnt after so long but you can't see this because of the jacket on the wire.its is possible that a wire somewhere in the harness has failed so really look good. Best bet is to have a continuity test light and start working your way through each circuit, I usually start at the component( light) and w9rk my way back to the fuse panel.sorry if I steered you wrong with the fuse boxes. I drive a 98 which has a lot more electronics than your 86, but I can say this with electricity, when you turn on a switch, you are basically connecting two wire together which allows current to continue flowing from an already to go live wire to the component and if it don't work then there is a bad connection somewhere in between the two( switch to light) good luck hope this helped

 

OK. I started by bringing a wire from battery positive to the green-with-white hot lead of the left front parking light which was not working. The left front parking light came on. We traced the green-with-white wire up to near the firewall, connected the wire from battery positive to the green-with-white wire and the parking light came on. I am unable to find the green-with-white wire inside the cab where the harness comes through the firewall. Would it be ok to unplug the connector from the headlight, connect one of the leads from a DVOM to the green-with-white wire just before it goes into the bulb in the front of the vehicle then touch each receptacle on the headlight plug until we get continuity THEN attach a wire from battery positive to the receptacle where we got continuity and see if the parking light lights? As you can tell, I am not an electrical whiz and am just trying to work through this so any helpful pointers are welcome and appreciated.

 

Check all the ground connections to the body and such, make sure they are all making good contact.

 

I would like to check the ground but have no experience reading wiring diagrams. Does anyone know where this circuit (tail lights / marker lights / seatbelt buzzer) is grounded? Thank you.

 

The grounds will always be black wire.usually for tail lights and such the ground wire will come off the light at the end of the circuit and be mounted somewhere close to it on the frame.find the black wires and trace them to where they end.anywhere you see a black wire mounted to the body or frame of the truck will be a ground

 

Understood. Checked the grounds for the parking lamps and marker lamps in the front of the truck and they were all clean and tight. I failed to mention that each front parking / marker light and each tail light will light up if we run a wire from battery positive to a push pin inserted into the hot wire for the light just before where the hot wire enters the light receptacle. Doesn't this confirm that the grounds are good? I am unable to tell if there is any relay involved in this circuit - do you know? Sorry for so many questions but I am really struggling here.
Thank you.

 

Well I'm not a mechanic like I said or an electrician but I have messed around a lot with these sort of things, I'm just hopeful that what I'm telling you is helping you out, yes it sounds like your getting power so no ground issue, its gotta be somewhere in the constant power wire that's blocking the power from the lights. Did you check all the lights that are out, pull em and look for any melted together wires, I'll pull up the schematics on your truck and have a look, see if I can't figure this out. Which lights were the first to go out?.

 

Over the past month, the instrument cluster lights got dimmer each day until they finally went out. I was putting off fixing the instrument cluster lights when the policeman stopped me and said I had no tail lights. Sorry I do not know when the tail lights actually went out but I am guessing it was the same time the front/back parking lights, front fender side marker lights, and license tag lights went out since they are on the same fuse as the tail lights. Thank you.

 

The problem has got to do with the instrument panel then I'm sure. Your gonna have to open that up and get at the wires connected to the panel, I'm sure you don't want to open that can of worms up but you've traced it back to the firewall and have no ground issues, so its somewhere between your cluster and the spot where your wires go threw the firewall from inside to me it sounds like some wires got hot and melted together which will slowly cut off power , remember what I said about really looking at the wire good, it gets old and weak and could break off inside the jacket so don't rule that out when your going threw this trouble shooting,.maybe somewhere in that wiring harness you got wires that broke off of the connection they were making, cause like I said the wire gets old.

 

Is your truck the camper special, fordman says they had a relay somewhere up behind the instrument cluster that was installed for hauling a camper, to carry the extra voltage, has a lead that goes to the solenoid and to the battery negative I think and put 12 v directly to the cluster which could be messing up.

 

Your responses are helpful and appreciated. No, my truck is not the camper special. It is an F-150 Lariat long bed 2WD, 302EFI, auto trans. I removed the instrument cluster, disconnected its (20 lead?) power connector and made the photo shown on the left below of the power connector. The wires on the power connector look new, do not feel brittle, and are wrapped with yellow tape starting just below the power connector plug. Following the yellow tape, I can see through an opening in the dash a connector hanging loose however I could not find a corresponding plug for the loose connector. Do you know if this loose connector could be the "camper connector" mentioned in your 2:53 am post this morning? It seems unlikely that it would have just come unplugged for no reason. I was unable to get the cable out of the back of the speedometer- do you know how to disconnect the cable from the back of the speedometer? Please let me know more photos would help. Thank you.

edit: I searched the area around the "connector hanging loose" (pictured below on the right) and could not find a corresponding connector so possibly the connector is for a feature not included with my truck.

 

Sorry was out for abit, did you get it solved, I m looking at a diagram for the fuses, #14,15,21are the main 3 fuses running all those lights but the one I'd focus on is the #14 cause it has the most to do, the other 2 are for the cluster, according to my schematic. I'm going out to work in the garage today, I'll try a few things on my 97 see what I come up with, my neighbors an older guy who knows a lot as well I'll pick his brain too, good luck.