I'm no expert in 69 wiring, but I've never heard of a resistive feed wire for the gauges. Can you explain it to me a bit, and maybe I can cobble you up a surrogate?

 

There is a resistor wire going to the coil, but the gauge feed wire is a full 12 volts. The Constant Voltage regulator snaps onto the circuit board with connectors like a 9v battery. It's the CVR that drops the voltage to the gauge.

I'm really not sure what wire you're talking about unless you're referring to one of the traces of the circuit board. If that's the case, the circuit board is made in reproduction, and it's one part that is worth purchasing.

The PO of my car had a bare ammeter gauge wire in the engine bay. It fried the wire halfway across the engine bay, fried the ammeter gauge and melted the circuit board. I cut out the bad wire, spliced in new and replaced the circuit board with a repro. Ammeter gauge still doesn't work, but the rest is good as new (I could care less about the ammeter gauge as they're pretty much worthless gauges to start with).

 

I've got to concur, there is no wire for the instruments that incorporates a resistor that I'm aware of on the '69-'70s. The famed pink wire (resistive for coil) does not relate to the guages. I went through the wiring diagrams, and I don't see anything that is marked as a resistor, nor have I seen any wire that looks like a resistor (no markings on any of the harnesses I've looked at, and I've got 7 in the basement.)
What test are you running to determine that its open? A factory CVR will cycle between open and closed (12v and 0V), which will show as open on almost all digital multimeters. Try it on AC, or put an analog multimeter on the lead at the water temp sensor, does it fluctuate? I know, crazy design. I've replaced both of my factory CVR's with the solid state units that are now available.
Its possible that you have a short, but you should be able to isolate it if you do. The only short I've seen is with the fuel sender wire having rubbed through in the trunk, generally in the area of the white cable tie behind the driver's side wheelwell.
Hope this helps,

Carl

 

I'm all set Midlife, I have what I need for parts. I'm suprised that nobody has heard of this.

You guys have got to look at the schematics. The wire is labeled '30A' and is Violet. A resistor symbol appears on the schematic along the path of the wire. It measures about 10.0 ohms and its about 5 feet long. It goes from a junction just past the 'A' - (accessory terminal, black/green wire 297) of the ignition to the input side of the voltage regulator. Its job is to limit the current and protect the gauges from surges going through the them. Probably because of that crazy voltage regulator that Ford uses. There is also a simular wire for the altenator that reads "do not cut" down its entire length.

Obviously Ford expected this thing to fry because they attached a spare wire (or test point)to the same cluster connector terminal. In the schematic its labled "blind lead" or "blind wire". this wire is black and runs back to the big Y in the harness just back from the cluster connector. You should see a bare wire sticking out of the harness there. You can actually test the resistance of the violet wire and the voltage going into the cluster (input to the voltage regulator) without removing the cluster.

 

The wire looks like any other wire except that it is about 5-6 feet long. If you were to unwrap a harness it goes from the ignition juntion all the way to the glove box and back to the gauges.

My test is a resistance test. one lead at the ignition accessories terminal - the other lead at the cluster connector and my meter set at ohms. I don't have a way to post the schematic so I'm going to e-mail you one. It should be noted that most publications do not include only partial schematics or ones for tach only cars. the best source is the Osborn Electrical Assembly manuals.

I wonder if I should write tech article about this wire and the voltage regulator.


P.S. I'm an electrical engineer.

 

Holy crap! You are absolutely correct! I have never noticed it before, but the Pro Products wiring schematics clearly show wire 30A as violet resistance wire. It is the same for both tach and non-tach cars.

I stand corrected, and bow to your knowledge. I never knew that was a resistor wire, and am totally befuddled as to how I didn't have to replace it when I redid all the fried wiring in my car.

 

ManyC
You are almost correct, for the non-tach warning harness there are two internal wire resistors for the tach warning harness there are three internal resistor wires. They are as follows:
1. 16A (Pink) = 1.5 ohms
2. 30A (Violet) = 8.5 ohms
This is your famous ignition switch resistor wire. Notice that your ohms reading is a little high, about 1 ohm higher than the top end of the 10% tolerance.
3. 904 (Violet) = 1.5 ohms
All resistance is based on the stand IEE (10%) tolerances.
Hope this info helps.
Good Luck.

 

BTW,
I am the only one since 1978 that had Ford open up the vault blueprints to get these resistance values. It took me two years to get these SECRETE resistor values. I hope that this clears the air.
Solo2

 

thanks for the actual values. Its nice to know I'm not insane.... my meter hasn't been calibrated in 15years so I'm not really suprised that I'm off by 1.5ohms.

 

Here is another tid bit.
The pink wire that everybody points out that goes from the tach to the coil is that (16A) wire.
That resistor wire, 1.5 ohms is absolutely necessary for the tach. Both "TACHMAN" and myself had a long discussion on that topic. That small resistance is needed to limit the ampreage to the tach circuit board. Otherwise the circuit board gets too much amps and melts the vintage circuit board solder welds and saturates the tiny transitors.

 

So do you agree with the 3 wire system he uses for the Mustang tachs? It's a little over my head but seemed to make sense.

 

Are you talking about the thick wire in the engine comaprtment loom that runs along the passenger side of the engine compartment, pretty close to where the alternator wiring harness plugs in? If so, I had the same "fried" problem on my 70. I just cut out the bad part and spliced a regular wire into the harness. No problems afterwards.

 

Nope. I'm talking about the wire the runs from the ignition up to the instrument cluster. The one you fixed sounds like the alternator wire.

 

"So I was wondering, what do people do when they don't have a spare resistive wire? Do they just put in a copper wire and have their gauges off?

(Do they add a wire and a resistor ? Do they take one out on a spare harness like me or is there a source out there with the correct wire ? ")

To finally answer your original question is yes. Just solder in a standard 1/2 watt resistors making a total resistance of 8.5 ohms, that is what I did and that is why I needed to know the resistance values of those UNKNOWN resistor symbols. Been working fine for over 25 years.

 

This is really helpful. So much that i joined the VMF.
I do have a question about this... If the violet resistor wire with 8.5 ohm resistance us a 1/2 watt resistor, then what wattage is the 1.5 ohm Pink resistor wire?

I have a 69 cougar xr7 convertible and I'm in the final stages of major restoration. Once I get the tach connected and a coolant leak traced, I'm ready to put it back on the ground and take it out!

 

Hello its very good information but my question what to do if that cable ir burned like mine may i weld a resistor in between?
thanks

 

If I understand your question correctly, it was answered above. You will need to replace the wire and solder in a resistor of the correct value.