I took out the gauge cluster to clean it up and re-wire everything (it looks like a bird's nest in there!!) and there is a purple-ish pink wire labeled "Resistor Wire Do Not Splice or Cut". Well, a PO did just that and I'm against cab fires!!! It is in the printed circut connector and shares a pin with a black wire. I traced from the connection through the foil in the printed circut and it goes to the voltage regulator. I need to know where this wire ( and the black one) goes to at the other end as I can't trace it very far thanks to the PO. It isn't in any of my wiring diagrams, so I'm lost. Any help as to the function or the source would be greatly appreciated. So thanks in advance!!

 

Pink resistor wire eventually leads to the + on the ignition coil.

Josh

 

I believe that there are actually two resistor wires in this era electrical system: (1) the resistor wire that fields the coil, and (2) the resistor wire that powers the voltage regulator for the gauges.

If you're talking about (2), then I'd really like to know what you find out. I am in the same situation with my '73 Galaxie that I'm rewiring - I thought that 12 volts would go straight to the voltage regulator, but instead the regulator is powered through a resistor wire. I have seen the same item in wiring diagrams for similar-era trucks. However, in the diagrams I have found, the wire is shown as BLACK/GREEN so I'm not sure if we're talking about the same thing. It's possible yours is just a hack job. Here is a link to a 76-78 diagram:

http://repairguide.autozone.com/znet...528004bba0.gif

The reason this came up was because on my Galaxie, the resistor wire powering the gauge regulator is burnt up, and I was about to replace it with one from another vehicle. However I measured the resistance of mine and the one from the donor vehicle, and found them to be different. I posted a question about it in the Electrical forum, but didn't get a whole lot of traction. Here's a link to my thread:

https://www.ford-trucks.com/forums/1...stor-wire.html

Anyway, to answer your question, my understanding is that (at least on some years) the power to the instrument cluster voltage regulator is dropped down from 12 volts. It doesn't completely make sense to me since the input voltage to the regulator would then depend on the current drawn by it. It must be to limit the current for one reason or another. I just didn't understand why two vehicles, with what I thought would be pretty much the same gauge setup, would have different resistance values running to them.

Sorry I can't be of much more help - if anyone else has any more information, it would help me out a lot too.

 

I found a diagram in my detroit iron manual that i can e-mail to ya ,but i only see a black coming off as #57 and going out of the cluster and hiting connect point 'c-207 'behind the gauges and then hitting plug connector # C-327,which it says is brown?

 

That regulator shouldnt have a resistor wire with it. The regulator is about the earliest form of pwm (Pulsed width modulation). All it does is turn on and off to give you an avg voltage, thats it.

 

thats what i thought b/c I did not see one on the diagrams

 

100% understood - but if you look at the diagram, it shows a resistor wire. However, after looking at this a little more and doing some more searching, I think it might actually be the shunt for the ALT light. What I need to do is pull the cluster and look more closely at the traces. The shunt would make a lot more sense because I don't see how it would make sense to drop down the input to the regulator. Thanks for your input.

 

It cant be for the regulator. It would be on all the time.
You need to chase it from the ignition switch not the alternator.

 

The voltage regulator receives keyed power at the "I" terminal through the ALT light in the dash. The ALT light is literally in series with hot-in-RUN from the ignition switch and the regulator "I" terminal. There is a shunt resistor in parallel with the ALT light so that the regulator can still receive power in the event that the ALT light burns out. Power applied at the "I" terminal is how the "F" terminal is first powered to initially excite the alternator, before the alternator begins producing current and closes the field relay in the regulator.

This shunt is what I think the resistor wire I'm looking at is for, but I have yet to verify. Later years have the resistor mounted to the back of the printed circuit.

 

Okay yall thanks for the input. I removed the dash completely to chase this stuff down and split some tape and cleaned the wires with a kerosene soaked rag. Also some PO had the cluster removed for some time as a lot of the wires' colors appear sun-bleached. The wire is either a black or dark purple. While looking, I found a second resistor wire that is black/green. So here are my results so far:

1) The resistor wire from the printed circut connector ( the black or purple wire) went toward the passenger side in the harness, then looped back to the driver side and factory splices into the heavy gauged black/green ignition switch wire. So this must be the cluster power wire. So leaves the question:
Q) What is this black regular copper wire that shares a pin with the resistor wire? The only black wires in there are ground wires, which could only mean its some type of by-pass wire to avoid over-powering the regulator?

2) The other resistor wire wasn't connected to anything and was buried inside a ton of tape. I chased it and it looped back and forth like the other wire and it factory spliced into the same ignition switch wire as the other. What the heck was this one for??

 

I don't think the resistor wire you're talking about in #1 is the cluster power. The warning lights, etc take a full 12 volts. There should be separate power that runs to the cluster. I think the resistor wire is for the ALT light shunt based on what I have read here:

https://www.ford-trucks.com/forums/9...ml#post8310864

It would certainly make sense.

The black wire that shares the pin with the resistor wire is not a ground wire; it's a dummy wire. It goes nowhere and should be taped off at the end. The reason for this is because the conductor of the resistor wire is too thin to be crimped to the instrument panel connector by itself. The short length of black wire adds thickness so that the thin resistor wire can be crimped at the end. If it were a ground wire, the resistor wire would fuse out.

What was the color of the second resistor wire in #2? The only other resistor wire is the ballast for the coil. It's usually red or pink and may have a green stripe. What color was yours?

 

The thing is, I have an ALT gauge, not a light. And the wire seems to power the fuel, temp, and oil pressure gauges; not the entire cluster. Sorry for the confusion.

Holy crap!! Why didn't I think of that!!

The wire from the printed circuit is either a black or a purplish color (lots of fading and deterioration) and the other that wasn't hooked to anything was black and green.

 

Three different resistor wires were used in 1973/79's. Only one per vehicle.

COLF12250A .. Resistor Wire, Ignition Coil (Motorcraft DY37).

61.49" long / Color coded PINK / 1.30-1.40 ohms resistance / #16 gauge wire.
----------------------------------------------------------------------------
D1AZ12250A .. Resistor Wire, Ignition Coil (Motorcraft DY84A).

60" long / Color coded RED w/GREEN stripes / 1.30-1.40 ohms resistance / #16 gauge wire.
-----------------------------------------------------------------------------------------
D7AZ12250A .. Resistor Wire, Ignition Coil (Motorcraft DY213).

49" long / Color coded Red / 1.30-1.40 ohms resistance / #16 gauge wire.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
One ICVR (Instrument Cluster Voltage Regulator) was used in all 1971/79 F Series Trucks, Econolines & 1978/79 Bronco's:

D1AZ10804A .. ICVR (Motorcraft GR513).
~~~~~~~~~~~~~~~~~~~~~~~~~~
Note: The original cluster backs used in 1975/79 F100/350's / 1975/80 Econolines / 1978/79 Bronco's were made from a compostion material that can TURN TO DUST before your very eyes!

In 1981, Ford came out wirh replacement cluster backs made of hard plastic. Some of the originals were replaced by these, some were not. These were also factory installed in 1981/91 Econolines.

E1PZ10848A .. Cluster Back-Use with Oil/Amp Gauges / Fits: 1975/79 F100/350 / 1975/91 Econoline / 1978/79 Bronco.

E1PZ10848B .. Cluster Back-Use with Warning Lights / Fits: 1975/79 F100/350 / 1975/86 Econoline / 1978/79 Bronco.

 

None of that matches what I've got in my dash. What the heck has happened to my poor truck?!

 

The more I study, the more jacked up my truck's wiring becomes. I've figured out that one of the wires powers the little voltage regulator, but the other one I'm not sure about. Lots of talks of ALT lights....with the sun-bleached wiring...the unused wire may have been for a light, but removed with a new ALT gauge. Also some PO did a hack job points back-conversion so there is no resistor wire going to the coil at all. Maybe it once lead to the coil but is a different color from factory for some reason? I plan on rewiring the entire truck....from front to back, top to bottom. So what would be the best way of rewiring the gauge so it's safe and 100% functional and also restoring the coil resistor wire? Like I've said before, none of my wiring diagrams show any resistance wires (or the respective resistance values) at all, so I was not expecting this...