Alright, none of my gauges in my dash work. But, when I apply power to either the fuel, temp, or oil wires that plug into the sending units I can make all three work. I already changed the constant voltage regulator and still nothing? I also tried to ground each one and I still can't get it to work. This has got me stumped!!! Any suggestions?
Gauges not working???
- Thread starter 69grande
- Start date
HistoricMustang
Active Member
I am lost with the electrical stuff, but I bet someone here will step up to the plate. Check the grounds again.
HistoricMustang
www.historicmustang.com
HistoricMustang
www.historicmustang.com
6Stang7
New Member
On the back of your gauge panel there should be a white or chrome looking box. This is the voltage regulator for your gauges, and it's very common for them to burn out. I would recommend replacing the volt. reg. and see if that solves the problem.
-Shaun
-Shaun
pabear89
Active Member
69grande said:
Check to make sure that you have power with the key on to the guage regulator.
by reversing the power from the sending units it is showing that you have a direct connection to the guage. what your lacking is power from the reg.
side.
key side should have 12v and gauge side should show about 7.5.
PB
bud4660
Founding Member
I thought the sending unit side went to ground to make things work?? So the gauges had the hot hooked to them?? If thats true, when you hook the hot to the sending wires and the gauges move then they would have to be grounded. 
12 volt power is applied to the IVR (or CVR whatever you call it). The IVR vibrates between 12 volts and 0 volts. The average voltage is thus 6 volts. Note this is 6 volts ac NOT 6 volts dc. Read with multimeter set to ac volts.
Instruments themselves are 6 volt guages (carry over from when cars had 6 volt electrical systems).
The output of the IVR connects to the guages (+) posts. The guage (-) posts are returned to ground via a switch or sensor. If a switch then the instrument is not scaled and simply turns off/on according to the rating of the switch (example, oil pressure reads when switch pressure = 15 lbs or more). Note in this example, oil pressure does not indicate actual oil pressure only the fact that you have oil pressure. This is the way all late model Mustang oil pressure guages work. If there is a resistive sensor, the rating of the sensor determines the guage reading. Typical classic Mustangs have fuel sensors varying between 10 ohms and 90 ohms. This corresponds to FULL and EMPTY respectively. The temperature sensor also varies between 10 ohms and 90 ohms . This corresponds to HOT and COLD respectively.
Troubleshooting EMPTY/COLD readings: If the guages have IVR voltage at the (+) post, then the return wire to the sensor or the sensor is bad. Ground the (-) post of the guage. The guage should read FULL or HOT. If the guage reads okay then lift the ground at the instrument. Ground the sensor end of the harness wire. If the guage reads FULL or HOT, the wire is okay. If it reads EMPTY or COLD, the wire is open. If the wire is shorted to the car body the guage will read FULL or HOT. If you have a fault now then replace the harness wiring. If the wiring checks out then replace the sensor.
Instruments themselves are 6 volt guages (carry over from when cars had 6 volt electrical systems).
The output of the IVR connects to the guages (+) posts. The guage (-) posts are returned to ground via a switch or sensor. If a switch then the instrument is not scaled and simply turns off/on according to the rating of the switch (example, oil pressure reads when switch pressure = 15 lbs or more). Note in this example, oil pressure does not indicate actual oil pressure only the fact that you have oil pressure. This is the way all late model Mustang oil pressure guages work. If there is a resistive sensor, the rating of the sensor determines the guage reading. Typical classic Mustangs have fuel sensors varying between 10 ohms and 90 ohms. This corresponds to FULL and EMPTY respectively. The temperature sensor also varies between 10 ohms and 90 ohms . This corresponds to HOT and COLD respectively.
Troubleshooting EMPTY/COLD readings: If the guages have IVR voltage at the (+) post, then the return wire to the sensor or the sensor is bad. Ground the (-) post of the guage. The guage should read FULL or HOT. If the guage reads okay then lift the ground at the instrument. Ground the sensor end of the harness wire. If the guage reads FULL or HOT, the wire is okay. If it reads EMPTY or COLD, the wire is open. If the wire is shorted to the car body the guage will read FULL or HOT. If you have a fault now then replace the harness wiring. If the wiring checks out then replace the sensor.
I already replaced the temp sending unit, oil pressure sending unit, and fuel sending unit and the voltage regulator on the back of the dash. Its weird that when I apply direct power to the harness to all three gauges I can make them work, but if I apply ground none of them work. So, wouldn't that mean that the ground is ok, but somewhere I'm the gauges are losing power?
pabear89
Active Member
Did you just answer your own question, Or is the voices again.
Geegee laid out a good road map.
Check the power side.
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