I have a 78 f150 and it has alot of wiring problems. most dash lights dont work, brake lights dont work, No blinkers at all except front right one when lights are'nt on. All front lights work except front bottom left (prob needs new bulb), front left side marker bulb is out, right rear side marker is out, driver side rear light dosent work and the other one is dim. Obviously my lights not working is a liability and i dont want to be responsible for an accident where somebody could get hurt because of my lights not working. Also it sometimes does weird things like the radio wont work or it will work but when i put it in reverse it will go out. I dont know the first thing about wiring so what do you guys suggest i should do? I was thinking maybe there are bad grounds but i need to know where some of the grounds would be first so i can check them. Also there are wires coming out of the back of my rear side markers that dont connect to anything. This truck has always had these problems since i got it, but i think i used to at least have 1 brake light and one rear blinker. I figure that the p.o. must have done a crappy wiring job on this thing and now i have to somehow fix it. Should i take this thing to a pro? Im thinking about it but i don't have a ton of money to spend. If anybody has any suggestions on what i can do i really want to hear them. thanks and sorry for the long post.

 

You should have grounds behind each tail light and maybe behind each marker light you will just have to trace wires To make sure you have juice. Use an "idiot light" or diagnostic light to do this. It will be time consuming but youre better off to do all you can your self or any buddies to help cause you will spend a lot of money at a shop to have them troubleshoot the electrical. The most important thing is the grounds. My suggestion would be to start at the light and work your way back till you find the loose connection.

 

the ground's for the front turn signal are on the inside of the radiator core support frame, look for your wire harness and you will find your ground.

the wires coming out the back side marker's?? are these the one's on the side of the truck or the rear of the truck? if they are on the rear it is probably something the PO hack wired in for pulling a trailer around

also check the ground strap from the motor to the firewall

 

First step it to buy a manual for the truck with a full wiring diagram. Next, get a test light if you don't have one already. Test light will help you narrow down the problem places and the manual tells you which wire does what. Grounds are a good place to start. Also check for corrosion in the sockets. My biggest problem was rust on grounds and corrosion in the sockets. I got lucky and didn't find a hack wiring job.
Good luck
Nick

 

These trucks are around 25 years old and the wiring in them was designed to last 5-10 years tops. You may have to go thru all of the wiring and repair or replace it with wiring from a salvage yard that can be repaired or from one of the generic wiring aftermarket companies. Either way you are going to have to learn about the wiring and electricals. Have fun learning!

 

thanks for the ideas guys, i guess im just going to have to check over everything i can. Is there any common problem areas i should check out?

 

Depending on your wiring skill level, you could start with replacing an individual wire or a section of wire harness. T-1st is right about just going through the wiring and get it over with. When I bought my 79, I took one look at the old wires and started ripping it all out.
I order my electrical stuff from del-city.com and have been satisfied with pricing and quality.
I think that in the long run, you will not only gain a lot of knowledge about how the electrical system is set up, but also the safety and dependability that new wiring brings. Added plus is that you can safely add more lighting, stereo stuff, etc etc at the same time. Be sure to use relays for all electrical loads.
Learn and then do it yourself - it will cost a fortune to pay someone to do it.

 

I have a few problems with my '76. Onr problem was the turn signal switch and I compounded this by getting a cheap replacement. the turn signal switch does a lot more than you think it would.

Get a good book or two for cross referencing (wiring diagrams can be confusing), a soldering gun, liquid tape, zip strips, etc. and either trouble shoot or there is an article in tech artiticles about Bronco re-wiring that I have been eye-balling, A good multimeter with long wires would help too.

 

All good suggestions, I have a couple to add...

Read this tech article. There are step by step instructions for testing and repair. It's about a '70 but yours is wired the same (only some colors may be different).

Be sure to solder all the connections and repairs you make. Solder the wires together and use heat shrink tubing or liquid tape. Use die-electric grease in all connectors and on ground points to prevent corrosion. Then you won't have a loose faulty connection giving you trouble in a couple years.

Marty

 

So Ive been working on this wiring the last few days, found some wires that are not even hooked up to anything. I also found out that spiders like to live behind my brake lights. Is it nessicarry to take off the steering wheel to get to the turn signal switch? In the manual it says I have to but i cant figure out what the switch even looks like anyway, plus it says i need some kind of puller to get the steering wheel off. Also there is this plug looking thing on my brake on the metal part with 2 black wires and 2 red wires coming out. what is this thing for, i want to know because 2 of those are cut off. Also is it normal to have what i would call plugs or connectors under the hood that arent connected to anything. There are 2 on the drivers side and one on the pass. side and they look like something should be plugged into them like the others. Another thing is on the fuse panel, the fuse for the inst. panel is missing, theres not even the little metal pieces that hold the fuse into the slot. I think the p.o. said when i bought it that he wired a single bulb behing the inst. panel to light it up. Maybe thats where everything got screwed up, is it possible that my problems could be from something in the cab under the dash? and not in the outside wiring or at the lights? the blinker indicator arrows dont really work right either, the right one comes on and stays on with the headlights and dosent really work right. Also when i have my left blinker on without the lights on it works except that the right side also blinks but not as brightly. I do have a brake light on the left side when the lights are off with a dim right side brake light but with lights on there is no brake lights, just tail lights. Im sorry for all the questions and writing so much and I appreciate every reply.

 

It sounds as if your truck has been wired by some caveman. You need to find a donor truck wiring harness or get one of the universal kits.

 

Boy, sounds like you have a nightmare on your hands. Did you get a repair manual with wiring diagrams yet? It will be a big help. It is normal to have some connectors under the hood that aren't hooked up to stuff. Don't worry too much about that yet. The instrument panel fuse missing... don't know about that one. It sounds like someone jumped power from R or L brake to power them both and that's why you get double blinking. There should be a wiring connection on the rear D side of the frame before the tail lights. You can unhook it there and use the test light to narrow down if the problem is before or in the tail lights. The wiring diagram helps here. If you don't have one I can do some checking and let you know.
As far as blinker indicators, they are always a pain in the a** and I just decided to save the headache and live with it. Sounds like your turn signal switch works. That might be a little good news for you
good luck
nick

 

Yeah, i got a repair manual. I got the Haynes. It has wiring diagrams in the back but I really dont know how to understand a wiring diagram. I will check out the connection on the rear d side of the frame. It seems like there was something going on back in the rear and under the bumper, maybe wiring for a trailer or something. I think the turn signal switch is working. But that fuse missing for the inst. panel is confusing.

 

Hey 78custom,
Don't feel bad brother. I'm in the same boat. My lights are a mess. The t-signal stays on inside the cab, the instrument panel lights work when they want to. I had to rewire the marker lights on the roof. I don't whant to run a new harness!!! My truck has alot of wires leading to no where. I'm not to conserned about them. The P/O also did alot of add on lights. I cut all those off. Good luck brother, I'm right there with ya

 

You can take a course in basic electricity at a jr college etc. That will help you understand what you are doing and how to read those diagrams.