I'm new around here, so go easy on me.

I've got an '85 F250 with a stock 6.9L. I haven't done any mod's to it, but the engine is pretty new (45K miles and 4 years old). I've replaced pretty much everything attached to the engine, and even more, all done about 4 years ago when I replaced the engine. I'm pretty mechanically inclined, but when it comes to electrical work, I'm just dumb, and get frustrated easily.

Since I bought the truck in 97, I've always had some minor electrical gremlins. The GP ignitor would never last more then a few days. I replaced it twice when I first got the truck, hoping that it would last, but no dice. I've since just bipassed it with a push botton control. The dash lights have been a similar issue, and I've changed every bulb, relay, and voltage regulator I could find associated with the dash lights, but it blows a fuse within a few days every time, and then I'm literally driving in the dark. A mini-mag light is a must for night driving!

Now, after 14 years, I've begun having some new electrical problems. First, I discovered that the rear turn signals would both flash together when I put either the right or left signal on. The fronts worked just fine. I changed the turn signal switch in the column hoping this would fix it, but to no avail. Do to lack of time, and the fact I needed it up to snuff, I took it to a shop to address. They traced down three different issues where wires were shorted, and repaired them, and that corrected the issue. However, after two days it blew two fuses and then the turn signals nor the brake lights would work. I took it back, and they changed the fuses, tested it for about an hour driving it around etc., and it held. The next day after 15 minutes on the higway, the fuses blew again.

The problem is that when the truck is just sitting there idling, no problem can be found. It seems to only be an issue when driving, and in particualr, at highway speeds (it lasted for several days just driving around town below 45mph). Again, I'm no electrical wiz, but this suggests a short somewhere that only grounds out when I hit a bump or something, or a problem with a voltage regulator that at higher rev's it can't handle the output of the alternator (that even sounds kind of silly to me, so please don't laugh).

I'd take it back to the shop, but A) I just moved to 3 hours away, and B) given the nature of the issue, I don't know how they can trace it down idling in a shop. I've had some mechanic friends of mine suggest that the fuse block itself may be the issue. Does that sound like a possible culprit, and if so, any thoughts on where to find one (LMC or rockauto don't seem to carry it). Any help is much appreciated.

 

Old wiring lol. Mine is a mostly from late 81 and it is showings it's age as well. Bout the only thing to do is rewire the truck. I have searched for but never found a new replacement harness for the truck. I think our only option is a self or pro made harness. I now that on mine some wires are ate up inside the insulation in places you would never notice.

 

kenpobuck is probably right about old wiring insulation gets old and cracked wire develops stress fractures from flexing and vibration. There is nothing as hard to find as an intermittent problem you are never sure its fixed until it fails again unless you find an actual bad part. Sounds to me like you may have more than 1 problem. If you are in the Austin TX area we might get together and have a go at some of the major problems

 

I have an electrical gremlin too...he seems to like running around in the back of my truck, locking up the trailer brakes once in a while, or turn signals, or brakes or something....

 

Thanks for the help guys. I have figured as much, but held out hope that someone may have been able to say "yep, change out your..." Anyway, since I posted the OP, I went ahead and put two new fuses in (one for Turn Signals and one for Brakes), and the turn signal one blew as soon as I turned on the turn signals with the truck stationary and not even running. The brake lights have held now for several days, even after about ten minutes of highway driving at 75MPH.

I'm thinking that the two are linked somehow, and the brake fuse only blows when both the brakes and turn signals are on at the same time. I ran out of time to try and trace down the problem this weekend, but will get back on it this weekend. Hopefully it's nothing too involved.

 

Sounds like wiring is grounded out somewhere. hard as hell to find the damn things but a wiring diagram of the system would be helpful. PLC7.3 usually has those kicking around. Maybe he will post in here or someone else but if you can inspect all of the harnesses and any connections that would be a start.

 

Sounds to me that you have a short somewhere between the cab and the rear lights. Start by checking under the bed at the rear, I see so many cases where trailer plugs have been added and wires are taped up. After a number of years even the best electrical tape will begin to fail, leaving the connections exposed to a short. A bare wire that is causing fuses to blow regularly should be fairly obvious.
If I were closer I'd say bring it by, I love chasing electrical gremlins

 

Thanks guys. I've got a couple of different books with the wiring diagrams in them, but those things are so hard for me to follow some times. I'm used to looking at Piping drawings, or mechanical ones for work (construction), but electrical has always been my weak suit.

I've inspected everything I can see with the dash inlays removed, and when I replaced the turn signal switch in the column, I checked the existing harness on the column going back, as well as everything going into the fuse block.

I need to check the wires under the bed for sure. My dad and I are planning on tracing stuff this weekend. He was an electrical engineer at one point (the 50's), but also had his own shop for about 10 years, and he used to most of the electrical work there. He's just a little slow these days, and I'm not the most patient!

 

When I'm chasing an intermittant like you're talking about, I take a bad fuse and solder two wires to it. Then I connect them to a headlight. That way it will never draw more than the headlight when it does short out. During normal operation, the normal current draw won't be enough to light the headlight. At least you won't be replacing fuses and you will know exactly when your short occurs. That may help figure out what is happening.

 

Do yo have a trailer cord that got mashed? Fuse block won't short to ground unless it is bouncing around which would still pretty hard to do because it would have to spin around and hit the body. Find the spot where these circuits meet and you will find the problem most likely. When ever you have several things messing up look for their common location first.