Wiring Problems
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Wiring Problems
My 1985 6.9l f250 has been a pain in the butt when it comes to wiring. The wiring inside the dash shorted out and caused a small electrical fire inside the dash. Luckily, I had tools to take the trim off and put it out real quick, but now I have to do some rewiring. That being said, I am thinking it might be time to replace all the wiring and do it the right way. What is the best way to do this? I have thought about making a custom fuse and relay box, so that all wires coming from inside the cab are solely signal wires running to external relays to run the lights, blinkers, wipers, etc. Has anybody done this, and what is your experience?
(I am about to have surgery and wont be able to do it soon, so I have plenty of time to plan out what the best way to do it is.)
(I am about to have surgery and wont be able to do it soon, so I have plenty of time to plan out what the best way to do it is.)
Fleet Mechanic
Joined: Mar 2014
Posts: 1,926
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From: Saskatchewan Canada
Strange thing is, I find good wiring harnesses all the time. The cabs rot out long before the wiring disintegrates and as long as there are no poorly executed repairs, or bad accessory wiring, the factory harness is the best way to get the job done.
That said, your 6.9 requires a unique harness and the layout of the 86 and earlier wiring harness is a bit of a pain to remove and reinstall.Set some goals for what end result you want. What are you doing with this truck? is it a daily driver? Modified show truck? dedicated off roader? Trailer hauler?
The relay solution you propose is an acceptable way to wire a vehicle, but it will complicate your wiring immensely. There are some parts of the factory wiring that would benefit greatly from such an approach. Headlights and heater motor come to mind. Your glow plug heaters may already have such an arrangement.
I would look for a gently used harness that matches your year and powertrain. You could go with one of the relatively inexpensive hot rod style harnesses, but they will need to be adapted to every specialized plug in your vehicle and will likely be far more trouble than finding a good factory harness, or repairing yours.
That said, your 6.9 requires a unique harness and the layout of the 86 and earlier wiring harness is a bit of a pain to remove and reinstall.Set some goals for what end result you want. What are you doing with this truck? is it a daily driver? Modified show truck? dedicated off roader? Trailer hauler?
The relay solution you propose is an acceptable way to wire a vehicle, but it will complicate your wiring immensely. There are some parts of the factory wiring that would benefit greatly from such an approach. Headlights and heater motor come to mind. Your glow plug heaters may already have such an arrangement.
I would look for a gently used harness that matches your year and powertrain. You could go with one of the relatively inexpensive hot rod style harnesses, but they will need to be adapted to every specialized plug in your vehicle and will likely be far more trouble than finding a good factory harness, or repairing yours.
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Joined: Nov 2020
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Strange thing is, I find good wiring harnesses all the time. The cabs rot out long before the wiring disintegrates and as long as there are no poorly executed repairs, or bad accessory wiring, the factory harness is the best way to get the job done.
That said, your 6.9 requires a unique harness and the layout of the 86 and earlier wiring harness is a bit of a pain to remove and reinstall.Set some goals for what end result you want. What are you doing with this truck? is it a daily driver? Modified show truck? dedicated off roader? Trailer hauler?
The relay solution you propose is an acceptable way to wire a vehicle, but it will complicate your wiring immensely. There are some parts of the factory wiring that would benefit greatly from such an approach. Headlights and heater motor come to mind. Your glow plug heaters may already have such an arrangement.
I would look for a gently used harness that matches your year and powertrain. You could go with one of the relatively inexpensive hot rod style harnesses, but they will need to be adapted to every specialized plug in your vehicle and will likely be far more trouble than finding a good factory harness, or repairing yours.
That said, your 6.9 requires a unique harness and the layout of the 86 and earlier wiring harness is a bit of a pain to remove and reinstall.Set some goals for what end result you want. What are you doing with this truck? is it a daily driver? Modified show truck? dedicated off roader? Trailer hauler?
The relay solution you propose is an acceptable way to wire a vehicle, but it will complicate your wiring immensely. There are some parts of the factory wiring that would benefit greatly from such an approach. Headlights and heater motor come to mind. Your glow plug heaters may already have such an arrangement.
I would look for a gently used harness that matches your year and powertrain. You could go with one of the relatively inexpensive hot rod style harnesses, but they will need to be adapted to every specialized plug in your vehicle and will likely be far more trouble than finding a good factory harness, or repairing yours.
I’ve done some more reading about this truck specifically today.
I don’t believe that this drivetrain is very difficult in terms of wiring. To make it run, you basically need power going to the injector pump and power to the starter and glow plugs to start it. Basically everything else is accessory.
What I believe happened is the wiring was shorted out somewhere and burned out the headlight switch. I had to replace it twice, assuming that it had gone bad because it was cheap, but now realizing it was because of the extra draw. I then installed a rocker switch that wouldn’t mechanically fail, so the wires got real hot instead.
I think I’m going to go the relay route. It may not be pretty, but I believe it’s safer than the factory harness. I’ll try to update this post in case anybody else decides to do the same thing so that they can have some sort of reference.
Logistics Pro
Joined: Jun 2017
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From: Edmond, OK
I'm interested to see what you do to your Bullnose. I too have had wiring difficulty in my 86 F250. From my experience and what I've read on our forum the 
OE wiring harness in our Bullnose trucks is pretty pitiful. I've also considered using a replacement harness but haven't made the jump yet. Keep us posted. 
OE wiring harness in our Bullnose trucks is pretty pitiful. I've also considered using a replacement harness but haven't made the jump yet. Keep us posted.
Lead Driver
Joined: Nov 2013
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What I believe happened is the wiring was shorted out somewhere and burned out the headlight switch. I had to replace it twice, assuming that it had gone bad because it was cheap, but now realizing it was because of the extra draw. I then installed a rocker switch that wouldn’t mechanically fail, so the wires got real hot instead.
The stock headlight switch has an automatic reset circuit breaker. If the circuit is overloaded for any reason (bulb drawing excess current, short to ground, etc.), the circuit breaker opens and cuts off the power. Since you don't want to totally lose your headlights at night, once the breaker cools off, power is automatically restored. This is great if the problem is only intermittent. Not so much if the excess current draw is still active, and the breaker will continue cycling. If it continues cycling long enough, heat will build up and the switch assembly will eventually get damaged.
If you replace the stock switch with a plain switch, you have basically no overcurrent protection in the headlight circuit. There's a fusible link way upstream, but it also feeds several other circuits, so is much heavier than needed to protect one circuit. The wires getting hot? That tells us something in the circuit is still drawing excess current. The original problem that seemingly killed the first three headlight switches is probably still there. I hate to be the bearer of bad news, but installing a different switch didn't fix anything, and took away the overcurrent protection that was operating as designed.
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https://www.youtube.com/watch?v=OWwOJlOI1nU
The stock headlight switch has an automatic reset circuit breaker. If the circuit is overloaded for any reason (bulb drawing excess current, short to ground, etc.), the circuit breaker opens and cuts off the power. Since you don't want to totally lose your headlights at night, once the breaker cools off, power is automatically restored. This is great if the problem is only intermittent. Not so much if the excess current draw is still active, and the breaker will continue cycling. If it continues cycling long enough, heat will build up and the switch assembly will eventually get damaged.
If you replace the stock switch with a plain switch, you have basically no overcurrent protection in the headlight circuit. There's a fusible link way upstream, but it also feeds several other circuits, so is much heavier than needed to protect one circuit. The wires getting hot? That tells us something in the circuit is still drawing excess current. The original problem that seemingly killed the first three headlight switches is probably still there. I hate to be the bearer of bad news, but installing a different switch didn't fix anything, and took away the overcurrent protection that was operating as designed.
The stock headlight switch has an automatic reset circuit breaker. If the circuit is overloaded for any reason (bulb drawing excess current, short to ground, etc.), the circuit breaker opens and cuts off the power. Since you don't want to totally lose your headlights at night, once the breaker cools off, power is automatically restored. This is great if the problem is only intermittent. Not so much if the excess current draw is still active, and the breaker will continue cycling. If it continues cycling long enough, heat will build up and the switch assembly will eventually get damaged.
If you replace the stock switch with a plain switch, you have basically no overcurrent protection in the headlight circuit. There's a fusible link way upstream, but it also feeds several other circuits, so is much heavier than needed to protect one circuit. The wires getting hot? That tells us something in the circuit is still drawing excess current. The original problem that seemingly killed the first three headlight switches is probably still there. I hate to be the bearer of bad news, but installing a different switch didn't fix anything, and took away the overcurrent protection that was operating as designed.
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