I'm working on getting autometer gauges in my 73. I have figured out most of the original wires at the plug on the back of the IP and their uses other than these.

I have a black wire and a purple wire going to a single connection. The purple is a solid wire and has keyed 12V. After cutting them loose the black had .02 V.

I think the purple is the resistance wire but have no idea what the black is for. Looking at the back of the panel...both went to some sort of pickup or doomagigee on the back of the IP. I want to use the these for my keyed 12 v source. Should I tie these together and onward to the gauges?

Also, next to those is a solid yellow and red that go to the ammeter gauge. How do those connect to the new volt meter? Do they even need to the Volt gauge?

Just trying not to blow this up.

 

Can you post a picture of the two wires that go together that you're talking about? The gauges in the instrument cluster are powered by a small voltage regulator; it looks like it connects the same way a 9-volt battery would. This device is powered through an 8.5-ohm resistance wire, built into the harness. However, my understanding was that the wire should be BLACK/GREEN and not PURPLE.

You have to be careful when measuring the voltage at the end of what might be a resistor wire. If you measure it open-circuit, no current passes through it, and it will appear as though it has 12 volts. However, if it's loaded, current passing through the resistor wire will drop the voltage below 12.

Resistor wires look different than regular wires; the insulation is thicker, softer, and feels different. Sometimes, at the instrument panel connection, the resistor wire is crimped together with a short "dummy" wire because the conductor of the resistor wire is too thin to fit the standard crimp terminals, so a dummy wire is added to provide enough thickness for the crimp terminal. The other end of the dummy wire is taped off.

An ammeter setup is totally different than a voltmeter setup. The RED and YELLOW wires were part of the shunt ammeter. All you need for a voltmeter is a keyed 12-volt source, like what would power the radio.

 

 

Apparently 1973 was one of those transition years as i have been unable to find any diagram that is specific to my truck which was a Camper Special. 1974 is incorrect as far as colors go anyway.
The black and purple in the pic both go to the pickup or whatever on the back of the IP.

I did not get a chance to see if the black was dead ended to today.

Should I use this purple wire for the keyed source or find another?

 

The purple wire in the first picture absolutely looks like a resistor wire because of the ultra-thin conductor. I'm surprised to see it's purple, however - this would need to be confirmed with a factory wiring diagram. If it is the resistor wire (which seems to be the case), then you cannot use it as a 12-volt source, because it won't be 12 volts once current passes through it. This would also affect the input supply to the ICVR (instrument cluster voltage regulator). Find another source.

Where does the other end of the nearby black wire go to? I would guess it's taped off in the harness, making it the dummy wire. The conductor of the resistor wire is too thin to fit in a crimp terminal on its own, hence the need for the dummy wire.

The item in the second picture is the ICVR. If the purple wire is indeed what is feeding the ICVR, then it confirms that it's a resistor wire (8.5 ohm).

 

Thanks for the help, sir