I have a 1967 Mustang, 289 Convertible on which the gauges all have suddenly become pegged hard over as soon as I turn on the ignition.
I have replace the voltage regulator, and still get the same results. With the voltage reg disconnected, I still get the same results.
Every thing works except not knowing haw much gas, or what the temp is, etc.
Any suggestions on where else to trouble shoot would be appreciated.
Thanks
Matt
Ground connection(s) to the gauges?
Jan
I would think if the ground to the gauges was bad the dash lights would also be dimmer or off.
I guess that the voltage regulator mounted on the back of the dash cluster is bad.
Rich
The OP said he replaced it.
For what it's worth.
The original gauges are insulated from ground by a small strip of fiber material with two holes for the electrical terminals. If a gauge is loose, or not properly mounted, and one of the terminals makes contact with the instrument gauge housing you will cause a short and blow your 5 volt voltage regulator. If you replace the voltage regulator without fixing the problem you'll just blow the new one too.
If you still have the problem I would suggest replacing the mechanical 5 volt regulator with a solid state one. It can get expensive trying to trouble shoot by the replacing the voltage regulator, as the mechanical ones cost 30 or 40 dollars where as the solid state cost about two dollars. You can find the modification instructions on the internet and you can buy the part required ( Solid State Voltage Regulator LM7805 ) at any Radio Shack.
Yes, but if power flows thru the voltage regulator then to the gauge then tthru the sensor to groung, why would the gauge still peg, if he disconnected it? I assumed he meant the voltage regulator under the hood....
Matt please let us know what you find out. Rich
I'm not an electrical expert but I think the voltage regulator under the hood controls the voltage coming from the alternator to the battery. The 12 volts required to run the car actually is supplied by the battery. The alternator function is to keep the battery charged and the, voltage regulator under the hood, just controls that charge. For example, a bad voltage regulator can cause a battery to be over charge and eventually the battery will die but the car will still run until it does.
The instrument panel 5 volt voltage regulator, regulates the 12 volts coming from the battery to the oil, gas and temperature gauges. It does this by means of Bi-metallic Arm with a heating coil wrapped around it and as the current flows through the coil it causes the arm to bend and separates the contacts on the end of the arm. When the arm cools it relaxes and bends back making contact with ground again and the cycle repeats itself. If you have a short in your 5 volt circuit it can cause the coil or the Bi-metallic Arm to draw to much current and they can melt or break and when this happens if the upper arm is in contact or fused to the lower arm your gauges will be pegged.
Hope this makes sense!
have you tried reversing the leads on the back of the instrument cluster my
65 had that problem
According to Mustang Monthly, the most likely cause of pegging is the regulator on the back of the instrument panel. Not the only possible, but the most common. Could it be that somehow you are unknowingly frying the replacement regulator?
MotorsForum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.