Wiring Conundrum(s) II. : Brake Lights and Oil Pressure

Zion

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Truck in question is a 1984 6.9

- Brake Lights

The PO removed the trailer brake wiring and ended up wrecking the rear lights circuit. I tore out the (complete) harness that included break lights and functioning trailer plugs off of a bricknose and have been thinking about grafting it in. The current state of the rear wiring is a rats nest, so I think it'd be easier to run the new harness after pruning off all of the wires I don't need. That being said, I don't know if the 'new' harness has the same plug fitting as the 84 under the hood. I would appreciate some advice on how to approach this.

- Oil Pressure

I installed a factory turbo kit on my truck over the summer and the turbo I bought had a segment of the oil pressure sensor wire still on it. After replacing the old pressure sensor with the turbo oil supply the old sensor wire was too short to reach so I just chopped it and spliced it with the length I had off the turbo. The logic behind this decision came from PBR and the rough observation that the sensor looked like it communicated via a singular solid wire. It seems either my intuition was (likely) wrong or the pressure sensing unit is dysfunctional because the pressure gauge reads high the instant the engine is operational and never changes.
 

DaveBen

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Is the wire going to the gauge going to an oil pressure sensor? Is there any other wires connected to the sensor wire or terminal? You should have one wire going from the sensor to the gauge and a wire going to +12vdc.
 

Nero

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Also note, the sensor is grounded through the block. If you use too much thread tape, ground will be poor and sensor readings will be askew
 

Zion

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Is the wire going to the gauge going to an oil pressure sensor? Is there any other wires connected to the sensor wire or terminal? You should have one wire going from the sensor to the gauge and a wire going to +12vdc.
The wire is still wired the same way it was when the engine was N/A and worked as intended. The only modification I made was splicing in the longer segment that came with the turbo so that the wire cap can reach the post on the sensor.
 

Zion

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Also note, the sensor is grounded through the block. If you use too much thread tape, ground will be poor and sensor readings will be askew
The turbo sensor is factory and was already threaded in when I bought all the pieces. I guess I should have asked if there was a way to determine whether or not the oil pressure sensor was bad or if the spliced sensor wire was the issue.
 

DaveBen

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The splice should not be an issue if it is clean. The sensor maybe the culprit. The oil pressure sensor uses ohms to show the pressure. I am not sure how it works; 0 ohms = no pressure, higher ohms = more pressure seems right.
 

Rdnck84_03

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Is it possible the sender is for the warning light instead of a gauge. Since it only turns the light on below a set pressure, so if that is the case the gauge should have one reading with the key on engine off and on startup should jump to a set spot and stay there as soon as the pressure reaches the set point when hooked to a gauge.

James
 

Rondo

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If you are going to rebuild the harness, just unplug it and lay it on your garage floor. Keep the same plugs and splice in the wires you need to replace. If the bulb sockets are the same use which ever are better. Add the wires for your trailer connection. Put in wire loom and tape it up. Plug it back in and you have a like new harness. Don’t rush and relax and take your time.
 

DrCharles

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Is it possible the sender is for the warning light instead of a gauge. Since it only turns the light on below a set pressure, so if that is the case the gauge should have one reading with the key on engine off and on startup should jump to a set spot and stay there as soon as the pressure reaches the set point when hooked to a gauge.

James
That same sender was used on nearly every Ford since sometime in the late 80's, I think. Although there is a gauge, it can only read zero or mid-scale because there is a resistor in the dash cluster (20 ohms, IIRC) in series with the lead to the sender.

Now if your dash is set up for the variable resistance sender (i.e. without that resistor), and you are using the switch sender, it will peg as soon as your oil pressure exceeds 7 psi...

The correct sender has a bell-shaped housing about 2" in diameter. The switch sender has a small bakelite tower and is installed with a socket.
 

franklin2

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I am getting ready to redo the wiring on the back of my truck. It can get pretty bad as the truck is used over the years and repairs are made. My plans are to run new wire using a trailer harness for most of it. I am not going to use Ford's wiring scheme.

I went and bought a plastic PVC box from lowe's, I think its a 4x4x4 box. And I bought a large romex connector fitting. I will punch a hole in the bottom of the box for a 1 inch conduit, the fitting is 1 inch.

I am going to mount the box where it's easy to get to at the rear. I then am going to go up the frame rail till the factory wiring looks good, and splice in the new trailer color code wiring to extend it to the new box.

The lightgreen/orange will get a yellow wire spliced to it.

The orange/lightblue wire will get the green wire spliced to it.

The brown wire will be spliced to a brown wire (how did that happen Ford?)

The black/pink wire will be spliced to whatever color wire I can find. This is the back-up lights

I have a blue wire I added running from the brake controller up front. That is long enough to make it to the box. If it's not long enough, it gets spliced to more blue wire for the trailer brakes.

After these wires are extended (if they need it) they will all run up into the plastic box. This box will hold all the splices. Since it will be out of the weather, I might use wire nuts. These are easy to modify and test things if needed during a trip. I can also use fairly large wire nuts, since there will be a lot of wires.

I have the taillights, the back-up lights, a 4 pin trailer plug, and 6 pin trailer plug, and a 7 pin rv trailer plug. So all of those components will need left and right brake turn wires, running light wires, and a ground wire (forgot that in the previous paragraph. So some wire nuts will have 5 wires going to them. The brake controller wire will go both to the 6 pin and the 7 pin rv plugs. So a wire nut for it also.

Stuff it all in the box and screw the lid shut. And now all the wiring on the truck will match all the trailer wiring on the various trailers.
 
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