Gauge cluster power

[mr_josh]

Well, I pretty much finished rewiring my truck today. All lights, starting, charging and some extras are working. The sticking point was the main power going in to the voltage regulator on the back of the cluster (and subsequently out to the other gauges).

Tracing the power-in side of the gauge voltage regulator reveals that is powered by a violet resistor wire.

Now, excuse me if this discussion's been had before, but does anyone know the resistor wire steps down the voltage to? What is the input voltage for the cluster voltage regulator?

[seattle67]

Something doesnt sound quite right Josh.

The power in should be a full 12vdc. The positive comes in on a black/with green stripe wire, and the negative on a black wire.

There is a pink resistor wire, but that originates from your ignition switch and is for the ignition coil.

[Thunderfoot]

The violet resistor wire is the "Exciter Wire" for the alternator.

[seattle67]

The violet resistor wire is the "Exciter Wire" for the alternator.

Good catch Shayne, obviously my brain is stuck in 1967

[Thunderfoot]

The violet resistor wire is the "Exciter Wire" for the alternator.

Good catch Shayne, obviously my brain is stuck in 1967

That's one of the wires I have burned into memory couple more years of studying the wire diagrams and I might get them all memorized

[mr_josh]

Thanks to the great pictures on this site, I can show you just what I'm talking about.



If you look at the bottom-left image (the "with gauges" pic), you see my cluster. Looking at the connector on the back, the top contact on the left side is the power in to the voltage regulator (if you follow the trace on the PCB, you see it run across the cluster, down, between the terminals of the amp gauge, and to the voltage regulator).

On my wiring harness, that was a purple resistor wire. If I'm reading this PCB correctly, the pinout for this connector should be (top to bottom, left side, then right):

*Left*
Voltage regulator power
Amp gauge
Coolant temp sensor
Fuel level sensor
Oil pressure sensor

*Right*
Amp gauge (don't know which side is charging circuit, which is battery)
Left turn
High beam indicator
Bulb ground
Right turn

So the question remains: why the purple resistor wire in to the voltage regulator? How much resistance does it provide?

[Thunderfoot]

I do see a Violet wire after the the Black/green wire on this diagram for the 72 http://www.fordification.com/images/sch ... _quick.jpg but is is not listed as resistive like the exciter wire is on this same diagram...
The whole purpose of the Instrument Cluster Voltage Regulator is to drop the voltage from 12V to around 6V for the gauges, so don't know why it would need a resistive wire in-line before the ICVR.
The part number for the ICVR is the same for up to 74 ford trucks so I looked at the newly posted 74 wire diagrams and see that it also shows the Black/green wire turning into a Purple wire when it uses the radio noise suppression (choke)before the ICVR but when it is not using this choke it just had the Black/green wire going to the ICVR http://www.fordification.com/images/sch ... r_3of8.jpg what they have going on there
The best way to tell what the resistance of the wire is, is to remove that resistive section of wire and measure it with on Ohm meter...

[mr_josh]

Thanks for the input. I think that's all the convincing that I needs to just give it 12v and see what happens.

I'm not 100% certain that it is a resistor wire, I am just inferring that from the fact that it seems to have the same insulation, diameter, and small number of strands as the violet wire that we know is supposed to be resistive. I didn't measure resistance on it because it's been cut, and I know that the reisitance wires are often resistive due to voltage drop over a precise length (and in fact, now that I think of it, when I was unwrapping the tape in the main harness, there was a loop of the violet wire taped in there, as if it needed to be a certain length but they didn't want to cut it down).

Well, this will require some pondering. I'll probably get sick of pondering and just wire it in there with system voltage and it'll probably be fine. Thanks again for the input. (And if anyone with a '72 wants to pull their cluster, key on the ignition, and measure the voltage at the purple wire on the back of the cluster, that'd be great