All accessory Power

[1st73mach]

Hi guys, im mainly trying to get my temperature gauge to work in my mach one but i cant seem to get it to work. I’ve traced the wire and it runs exactly as it should but its not getting that little bit of power that it should. Ive checked the fuse box and everything is connected as it should be. But ive noticed only 2-4 prongs are getting power at the meeting point. No power goes to anywhere else. The large yellow wire from the starter solenoid, the red with orange stripe wire, and an illumination wire are the only ones getting power. At what point in the harness should there be power given to all wires needing power? Im having a lot of electrical issues with this car in terms of things needing power but not getting it. 

 

[midlife]

It depends upon the circuit.  Gauges get their power from the ignition switch, which transforms battery power to ACC power when the key is in ACC or RUN.  From there, there is a resistor wire that goes from the ACC line (actually the power line at the wiper connector) to the dash cluster connector, providing power to the constant voltage regulator.  There is no fuse involved for that circuit.

 

[1st73mach]

It depends upon the circuit.  Gauges get their power from the ignition switch, which transforms battery power to ACC power when the key is in ACC or RUN.  From there, there is a resistor wire that goes from the ACC line (actually the power line at the wiper connector) to the dash cluster connector, providing power to the constant voltage regulator.  There is no fuse involved for that circuit.

Do you have any tips on how to locate this circuit? I’ve traced the red and white wire from the gauge, through the cluster, to the sending unit itself and i see no issues but i could be missing something if it could be tied to another power wire somewhere

 

[midlife]

Red/white wire is oil pressure.  Fuel is yellow/white.  Power comes from CVR through gauge to sending unit, where things are grounded.  To test your circuit, put key in ACC, remove sending unit connector, and briefly ground that connector.  For fuel, there are typically 3 pins: one signal, one ground, and one unused.  Only briefly ground the signal line and your gauge should peg; leaving it grounded will short the gauge and damage it.  If it doesn't peg, then a wire may be broken, a bad connector somewhere, a bad gauge.  Do the test and we can trouble-shoot from there.

If any of your gauges work (excluding the ammeter), then the CVR is working.

 

[1st73mach]

Red/white wire is oil pressure.  Fuel is yellow/white.  Power comes from CVR through gauge to sending unit, where things are grounded.  To test your circuit, put key in ACC, remove sending unit connector, and briefly ground that connector.  For fuel, there are typically 3 pins: one signal, one ground, and one unused.  Only briefly ground the signal line and your gauge should peg; leaving it grounded will short the gauge and damage it.  If it doesn't peg, then a wire may be broken, a bad connector somewhere, a bad gauge.  Do the test and we can trouble-shoot from there.

If any of your gauges work (excluding the ammeter), then the CVR is working.

Do you have a picture of what the CVR is and a location of where i may find this? Ive done a couple tests and they all failed, theres no signal going to any gauge whatsoever. 

 

[RD-72]

Captain obvious, putting his two cents worth in on the issue.

just double checking, as you didn’t mention it in your post

If I recall it correctly, assuming you are running factory gauges, I believe the temp gauge needs a voltage regulator (IVR) (attached to the back of you gauge cluster) so power goes into the IVR at ~12 volts and comes out in intermittent pulses, so it averages 5-6 volts (factory). The new solid state IVR’s apparently have power coming out at around 6 volts.

it may be possible that your IVR is shot?  Is your oil pressure gauge/gas gauge working? If so and everything is hooked up properly, then that might not be your issue.

good luck...as wiring can be tough to get working correctly, especially if you were having troubles before.  Who knows how much batching was done by a previous owner.

 

[1st73mach]

Captain obvious, putting his two cents worth in on the issue.

just double checking, as you didn’t mention it in your post

If I recall it correctly, assuming you are running factory gauges, I believe the temp gauge needs a voltage regulator (IVR) (attached to the back of you gauge cluster) so power goes into the IVR at ~12 volts and comes out in intermittent pulses, so it averages 5-6 volts (factory). The new solid state IVR’s apparently have power coming out at around 6 volts.

it may be possible that your IVR is shot?  Is your oil pressure gauge/gas gauge working? If so and everything is hooked up properly, then that might not be your issue.

good luck...as wiring can be tough to get working correctly, especially if you were having troubles before.  Who knows how much batching was done by a previous owner.

No gauges are working whatsoever, my rpm gauge doesnt work either.

Is this the part you’re referring to? If so im not sure i even have one of these, what wires connect to this? 

 

[RD-72]

That is exactly the part. Instrument voltage regulator (IVR). It is supposed to be screwed onto the back of your gauge cluster (on the speedometer side of the cluster...unless someone along the way butchered up the wiring.

if I remember correctly, the printed circuit on the back of the cluster, has the male/female plugs attached to it...so it’s a simple pug and play.

later today I can run into the garage and take a picture  from one of my spare gauge clusters...which should help you out

 

[Don C]

The tachometer and gauges not working are two separate issues, the tachometer works off the ignition circuit and the gauges/IVR are powered by the accessory circuit.

 

[RD-72]

So here is a picture of a printed circuit (courtesy of Epay), the connectors are on the tab hanging in the middle of the circle

the tach and non tach printed circuits are different.



the tabs to connect the IVR are built in and part of the circuit.

 

[RD-72]

Pictures as promised...of the back of the gauge cluster...but I stand corrected...the IVR is on the tach side (picture #2

 

[Steve McMahan]

I think you need a wiring diagram and a schematic; wiring is hard or impossible without those.

 

[Hemikiller]

Wiring diagrams are in the Wiki

https://7173mustangs.com/wiki/

The 73 shop manual has diagnostic procedures for the gauges. 

 

[1st73mach]

Pictures as promised...of the back of the gauge cluster...but I stand corrected...the IVR is on the tach side (picture #2

View attachment 56552

View attachment 56553

Do you know if the ivr has anything to do with the temp gauge or oil pressure gauge? Those are the ones im really concerned about. I tested the gauges they all work as they should but i cant get the sending units to give me a reading through the gauges. Im at a loss for these things right now. Something isn’t communicating properly and im not sure what. My sending unit wire doesnt have the pulsating power surge going through it like it should. Thats not the ivr that controls that power is it? 

 

[RD-72]

iVR (pulsing power or ~5-6 volts that comes out of the IVR) IS required to run the OEM temp gauge, oil pressure gauge and gas gauge (I don’t think anything else).  It’s as simple as 12 volts power coming into the IVR, 6 volts coming out....

BUT do not forget that the long metal attachment of the IVR acts as the ground when attached to the gauge cluster (which is also required).

 You might want to try a bench test with just the IVR to see if that is your issue. Be careful not to hook up and test it backwards....as all you will see is a big spark and likely will kill the innards of your IVR (don’t ask me how I know).

good luck

 

[1st73mach]

Alright so my new IVR came in, my oil pressure gauge is working as it should. My temperature gauge wasnt going up after 15 minutes of running. So i checked to see if i was getting power to the wire and it was but it wasnt a blinking power like i thought it should’ve been. Its at a constant low voltage, is there something im missing here? 

 

[Don C]

You probably got one that says "solid state technology" in the description. They are not an electro-mechanical regulator like the originals, but are all electronic, and provide a steady voltage. They are also non-adjustable.

 

[1st73mach]

You probably got one that says "solid state technology" in the description. They are not an electro-mechanical regulator like the originals, but are all electronic, and provide a steady voltage. They are also non-adjustable.

So is this going to be an issue with the temp gauge? 

 

[Don C]

No, it will have no effect on your temperature gauge, it actually should work better. Have you checked the sending unit? The resistance (ohms) should change as the engine heats up. The range is 70 to 10 ohms.