Another gauge cluster issue - Vintage Mustang Forums
 1Likes
  • 1 Post By Flade
 
Thread Tools
post #1 of 7 (permalink) Old 07-05-2019, 11:42 PM Thread Starter
Junior Member
 
Join Date: Nov 2018
Location: Bay Area
Posts: 3
Another gauge cluster issue

I know everyone has seen variations of this issue, but hereís mine and Iím hoping someone can help. I finally got my 67 fastback back together and everything works except the fuel and temp gauge.

The gauges, when I turn the key to the on position, both go to the high end (full or hot). Iíve replaced the sending unit on the temp gauge, and the voltage limiter ( I now have a constant voltage), and neither of these fixes corrected the issue. Iíve unplugged the wire from the temp sending unit and the gauge dropped, then when I grounded it out, it went to ďhotĒ again. I tested the voltage limiter and I was getting 12v out the back end. I thought that was high so I tested the old one and got the same. My questions are 1) what should I be getting out the back end of the limiter 2) is 12 volts too high and could that be sending everything out of wack, 3) should I/do I potentially need to ground my cluster to my dash (Iím told it grounds when itís installed but...?) and 4) am I missing something?
Tís 67 is offline  
Sponsored Links
Advertisement
 
post #2 of 7 (permalink) Old 07-06-2019, 07:02 AM
Senior Member
 
awhtx's Avatar
 
Join Date: Sep 2011
Location: The Hill Country of Central Texas
Posts: 8,980
If the gauges go to the high end of the scale as soon as you turn the key to On you have a short to ground somewhere. Or the wrong sending unit. Your '67 gauges work with sending units that operate within a 10 - 73 ohm range.
awhtx is offline  
post #3 of 7 (permalink) Old 07-06-2019, 08:31 AM
Senior Member
 
Join Date: Jul 2009
Location: Niceville Fl
Posts: 4,494
The wiring is pretty simple. 12V into the Instrument Voltage Regulator (IVR). It grounds to the back of the cluster where it is screwy on, but in 67 I think there was a wire from the cluster back to the car frame to improve the ground. 65/66 grounded through the screws that held in the cluster in place. Output from the IVR is a 5v average (original units pulsed to average 5V). Modern digital units are a steady 5v. The 5V from the IVR goes to the input terminal of the Fuel, oil pressure and Temp gauges. The output wire of the gauge goes to the appropriate sender. The senders ground to the car (fuel tank or engine)

As said above the senders vary the resistance between approximately 10 & 73 ohms. The higher the resistance the less electricity flows and the lower the gage reading. The lower the resistance, the more electricity flows and the higher the gauge reads.

Do your gauges go to the high end but stay within normal range or do they peg all the way to the right? If they peg to the right, you definitely have a short on the circuit and have likely fried your IVR and possibly the gauges too.

The other possibility is your IVR is bad or wired incorrectly and you are sending 12V directly to the gauges. This could likely fry both the gaguees and the senders. In any case you need to get this fixed ASAP. Do you have a good digital VOM for diagnostics?

Post a pic of the back of your cluster so we can see how you have it wired.
CJM68GT390 likes this.

Flade
68 289 convertible Candy-apple red & white
66 200 coupe Blue
94 GT convertible Red & black
98 GT convertible White & black
98 V6 convertible White & tan

Flade is offline  
 
post #4 of 7 (permalink) Old 07-06-2019, 03:50 PM Thread Starter
Junior Member
 
Join Date: Nov 2018
Location: Bay Area
Posts: 3
Guys, thanks for the feedback, Iím a newby to this site and owning a mustang, and the information and help from this forum has been very helpful.

I think I understand the basics of how the gauges work, but it sounds like I may have a ground/short issue, and my IVR is putting out 12v on the back end which sounds like it should only be 5v. I have just recently installed the AAW 510055 wiring harness, and with it the rewire kit for the back of the gauge cluster. Here are a few pictures. I believe I have the wiring correct, but I donít understand why both of my IVRís (old and new one) are putting out 12v? Is it possible I have two fault IVRís?

With regards to the gauges, when I turn the ignition to on, they peg as high as possible. Itís sounding like I have ground and IVR issues, any thoughts on where to start troubleshooting? Thanks everyone.
Attached Images
File Type: jpg C3BB28FD-1878-4709-A553-CF8A2D650CBA.jpg (425.5 KB, 4 views)
File Type: jpg 823A4FC3-3B6C-4B0E-BDBE-392B3EA66BE8.jpg (458.8 KB, 4 views)
Tís 67 is offline  
post #5 of 7 (permalink) Old 07-06-2019, 04:46 PM
Senior Member
 
Join Date: Jul 2009
Location: Niceville Fl
Posts: 4,494
Quote:
Originally Posted by T’s 67 View Post
Guys, thanks for the feedback, I’m a newby to this site and owning a mustang, and the information and help from this forum has been very helpful.

I think I understand the basics of how the gauges work, but it sounds like I may have a ground/short issue, and my IVR is putting out 12v on the back end which sounds like it should only be 5v. I have just recently installed the AAW 510055 wiring harness, and with it the rewire kit for the back of the gauge cluster. Here are a few pictures. I believe I have the wiring correct, but I don’t understand why both of my IVR’s (old and new one) are putting out 12v? Is it possible I have two fault IVR’s?

With regards to the gauges, when I turn the ignition to on, they peg as high as possible. It’s sounding like I have ground and IVR issues, any thoughts on where to start troubleshooting? Thanks everyone.
Ok, now we have something to work with! Pic always help. I am assuming you have. Digital VOM and know how to use it.

1st. Looking at your set up, I think you may have the brown and red wires reversed on the IVR. That would likely be the cause of your issues. The steps to check te system are.

Start with the setting on Volts DC. Put the negative problem on the ground screw that hold# the IVR to the cluster. Put the positive probe on the brown wire on the IVR. With ignition on, you should get battery /alternator voltage (12V or higher). Now move the positive probe to the red wires. You should get 5v if the IVR is working.

Next turn off the ignition and change your meter to ohms. Measure from the ground screw to the negative battery terminal. It should be a very low reading. Then disconnect the red wire from the IVR. Measure the resistance from the red wires to the ground screw. It should not be zero or close to it. If it is you have a short.

Flade
68 289 convertible Candy-apple red & white
66 200 coupe Blue
94 GT convertible Red & black
98 GT convertible White & black
98 V6 convertible White & tan


Last edited by Flade; 07-06-2019 at 04:56 PM.
Flade is offline  
post #6 of 7 (permalink) Old 07-06-2019, 05:20 PM
Senior Member
 
TheRktmn's Avatar
 
Join Date: Jan 2012
Location: Mills County, Texas
Posts: 435
This applies to the 'accessory' gauges: OIL, FUEL, TEMP. It does not apply to speedometers, tachometers or warning (idiot) lights. It is a basic overview, not a technical bible.

Ford kept things very simple with the gauges - less moving parts, less components to fail and for the most part no numbers. The exception to that last one is the oil pressure gauge.

The general rule of thumb with Ford gauges (other than fuel) is that centered is normal, slightly either side of centered is okay.

The acceptable low Oil pressure rule is 10 PSI for each 1000 RPM, so 2500 RPM = 25 PSI. That is pretty useless considering that the Oil gauge is the same functionally as the Fuel and Temp gauges.

Also, the gauge movements are NOT linear - 0 scale is 70 ohms, Full scale is 12 ohms. You would think that 1/2 way would be 40 ohms, but it is NOT. Half scale is 26 ohms!

Okay, how do they work?
There are 4 components involved:

The Gauge: Internally the gauges have a thin metal strip with a wire wound around it. This metal strip has the pointer (needle) attached to it. Electricity traveling through the wound wire heats it up. This heat is transferred to the metal strip, causing it to flex. The flexing makes the pointer move. Basically it is a mechanical mechanism triggered with electricity. Simple, right?

The Sending unit: The sending unit is actually a receiver, not a sender. Internally it is a variable resistor. The sending unit regulates how fast the voltage flowing through the gauge gets to ground. This resistance is what causes the heat that moves the needle.

The Voltage Regulator: Known as a CVR (Cluster Voltage Regulator) or IVR (Instrument Voltage Regulator). Do not confuse this unit with the big voltage regulator over by the battery. This voltage regulator is a small silver box that lives on the back of your instrument cluster. It's sole purpose in life is to limit the voltage going to your gauges. (The factory gauges are designed to use 5.5-6 volts DC (VDC) - if you hook 12VDC to one the smoke will come out and you will be looking for another gauge.)
The IVR is extremely simple and dependable. It uses the same coil, metal strip, heat principle as the gauge, but the metal strip has a set of points that the flexing metal opens and closes. This happens very quickly, resulting in an average output of about 6VDC. The two connections on the IVR are input and output. The IVR must be grounded through the case or mounting tab to function. There is one IVR to supply power to all of the accessory gauges. The 12V (input) side is marked with IGN.

The wiring: Gauges are probably the simplest, least understood circuits. Ready?
12VDC goes into the IVR.
The 6VDC output from IVR goes to the gauge.
The voltage passes through the gauge to the sending unit.
The sending unit regulates how 'fast' the voltage gets to ground.
It's almost too easy.


Simple Troubleshooting Tips:

All gauges swing to full scale:
- Faulty or miswired IVR



One (or all) gauges swing to full scale:
- Sending unit side of gauge is grounding to case.
- Short to ground in wire between gauge and sending unit.


All gauges are dead:
- Check voltage into IVR. It should be >= 12VDC.
- Check voltage out of IVR. It should be 5.5 - 6VDC.

One gauge is dead:
- Disconnect wire from sending unit, momentarily connect wire to ground (preferably through a 10 ohm resistor). Gauge should swing to full scale.
-- if gauge moves then sender is at fault. Check that the sending unit case is grounded with little to no resistance, replace sender if necessary. *It is common for replacement senders to be either the wrong value or wrong type. Always buy senders from a reputable supplier and double check the part number if possible.
-- If gauge does not move: check voltage at both sides of gauge, perform grounding test at output side of gauge (post not coming from IVR), check wiring circuit from gauge to sender.

Causes for inaccurate gauge:
- Faulty / incorrect sender
- Bad connections / high resistance in wiring circuit
- Gauge is out of calibration

Notes
- Do not use teflon tape or silicone on the sending unit threads as it can cause higher resistance. The sending unit should have a small band of sealer on the threads and will seal when tightened normally.
- A 'modern' sending unit will have 150 ohms of resistance so the pointer will not move at all.
- Oil pressure sending units for gauges are large bell shaped senders. The warning light sender is a small quarter sized unit.
- The constant heating and cooling cycles that the metal strips in the gauges and IVRs have gone through for 40+ years can cause the gauges to become inaccurate. Both can be calibrated with the right equipment.
- You will need an 'old' analog volt meter to check IVR output. The new digital meters will not read it correctly. You will not get a steady reading on the meter, it will pulse high & low and the average voltage will be about 5.5 volts.

Bob

Contact and business info removed to comply with new management ad rules.
TheRktmn is offline  
post #7 of 7 (permalink) Old 07-06-2019, 08:34 PM Thread Starter
Junior Member
 
Join Date: Nov 2018
Location: Bay Area
Posts: 3
Guys, thanks again for your help...like an idiot I followed the AAW instruction to the T, and it had the IVR wired backwards (at least based on my IVR). After following the steps Flade laid out, I confirmed this (aside from the fact it says IGN on the IVR). I switched the wires and everything appears to be working. I would never have thought the wires were backwards.

Itís nice to have the temp, fuel and oil idiot light working again.

Thanks again, this forum is great.
Tís 67 is offline  
Sponsored Links
Advertisement
 
Reply

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the Vintage Mustang Forums forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:
OR

Log-in










Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page



Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On
Trackbacks are On
Pingbacks are On
Refbacks are Off

 
For the best viewing experience please update your browser to Google Chrome