Back home, made some progress. Tested continuity on the oil switch OK Tested continuity from pin 10 of the cluster connector to the oil switch OK Found the red / yellow hatch wire in the engine bay area and follow it to the last connector in the engine bay it is still red / yellow hatch, continuity from pin 14 of the cluster connector OK but found a black wire cut wich the red / yellow hatch is connected going nowhere, and a device i don't know plugged nowhere. At the exit of this device the wire becomes from red / yellow hatch to brown with yellow dots, this wire running back threw the firewall...and going under a metal plate under the pedals (thought maybe for the seat belts light on the cluster....) The connector with the black wire cut The connector with the device. The device closer with its ref A diagram i made from what i found. Thanks. Eric
I just sent you a wiring diagram that contains more detail than the main wiring one which is posted to the site. It is a complete wiring diagram from 1973 but the wiring should be nearly identical with your 1975. We might have a minor distraction in what you are seeing under the hood. The Red/Yellow that you are seeing under the hood may be receiving power from under the dash harness and down stream from the dash cluster, used to enable a later device (emission/temperature activated control) but not primary to the warning light. The red yellow hatch wire under the hood to the connector that has the cut black wire was originally to a pigtail that ended at an emission control device (in this case a Ported Vacuum Switch that would close the circuit once engine temperature reached a specified range - obviously deleted sometime in the past (and not likely needed with all the time you've had the car). The "device i don't know plugged nowhere" is an ambient temperature sensor use either with the emission device in concert with the emission system or the air conditioning system (normally used to keep the air conditioning compressor from operating when the ambient temperature is below threshold (usually around 48 degrees F if memory serves. The cut black lead would be to a ground and with the emission control has no impact on your car as of this writing. I'm looking through some other, more detailed, wiring diagrams. That stated, I believe that you are looking in the wrong area for the Red/Yellow supplying power to the dash. These cars normally will not have a run out to the engine compartment and back - the power would be more direct from ignition to the light then out to the switch. I think the light gets power from the ignition switch, either at a connection or splice between the ignition and fuse block.
I concur. I just makes no sense for that red/yellow to go all over the place when it needs to go from the ignition switch to the instrument cluster. It seems to me that what is missing is a feed from the ignition switch to the red/yellow wire which needs to be somewhere between the instrument cluster and that connector for the ambient temperature switch. My assumptions are only based on my experience and the published diagrams. I have no first knowledge of the exact car although I do understand vehicle electrics
For some background info and because I've got the pictures to hand, this is the standard circuit that first appeared in '74. The wire colors are as per factory diagram(thanks to posts by 72GTVA) but seem to match what is in the car in question. You can see how the two warning lamps(oil and brake fail) are feed from pin 14 which is that red with yellow hash wire:
Which is what I had been saying all along. Pin 14 supplies voltage to the one side of the OIL light, and the pressure switch grounds the circuit when oil pressure is at or below the pressure that holds the switch contacts open, turning on the light. So pin 10 to the switch should be checked for continuity, pin 14 for voltage, and the switch for no continuity when engine is running/continuity when engine is stopped.
That is it in a nutshell and it seems that everything is working apart from the lack of 12V at pin 14. Exactly where pin 14 is fed from is proving elusive.
Okay guys, at first thank you all, i'm going to concentrate my searches in the interior of the car following the red/yellow wire from the pin 14 of the connector of the instruments panel and will let know. Just one thing, ther's no red/yellow wires connected on the ignition switch on the wiring diagram.....
Checked again the 75 wiring diagram, if you start from the pin 14 of the instrument panel connector and follow the red/yellow wire ( i painted it in blue on the diagram) it becomes red/light green after passing someting looking as a fuse (painted it in green), this red/light green split in two (painted in yellow), one going to the positive of the coil and the other going on what i surounded in the circle. Someone know what is this thing i surrounded in the circle ?
That is more of the ignition switch. It has to be as it feeds the ignition coil through the run resistor/resistance wire.
Yeah, as I recall, the wiring color does change after the ignition ballast resistor. I found that unusual.
Yes. If I recall, the wire from the switch to the resistor is one color, and the wire from the resistor to the coil is another color.
It is just a wire in all appearances, a little larger diameter and it has a different feel and flexibility in comparison to the other wires in the harness. It is color coded red/green stripe through most of the '70s era cars.
Most resistance wires I have seen in Fords transfer from the red and green color to what looks like a black heat shrink tubing covering. It will be about ten feet long and folded upon itself inside the dash harness. Starts out red and green at the ignition switch then it reverts to the heat shrink look within inches of the ignition switch then back to red and green close to the firewall bulkhead connector. Never found resistance wire on the engine side of the wire harness. Also never found any other circuits branching off from the resistance wire.
Okay, planning to go to the car saturday so will look for that. Thanks Hillbilly. According to the wiring diagram the red/yellow wire going to the pin 14 of the instruments cluster connector is connected to the red/light green wire going from the ignition switch to the positive of the coil ????
