Hey All,
New member, so please excuse me if this is a repeat...
I read the article on this site on how to fix the instrument voltage regulator in an early A body without removing the gas gauge. I hooked up the 67 regulator in my 66 Barracuda and the needles just barely moved, I removed the ground wire completely and they seem to be in the correct spot now (time will tell, when the motor cools, and as I use the gas in the tank). If you have any advice regarding the ground wire please let me know. I have another question related to the IVR. Does it control the oil pressure gauge as well? I have an after market oil pressure gauge hooked up at the moment and I don't want to go to the trouble of hooking the original back up just to find that it is the sensor, or the gauge, or something else. Any thoughts would be greatly appreciated. Here's hoping that I won't be running out of gas, or risking overheating in the future.

Warm Regards -MICHAEL ANTONIA

The regulator inside the gas gauge powers the oil and temp gauges too. To use an external regulator, you need to disable the gas gauge's old internal regulator and connect the new regulator to the gas gauge regulated output stud.

You can do that by just removing the +12 into the gas gauge (heat shrink tubing over the stud would probably work well), or, alternatively, you can just disable the regulator inside the gauge by wedging a small insulator between the points to keep them open. In either case, the heating element of the old regulator will still get power, but won't accomplish anything.

The only complaint I've heard of using a LM7805 electronic regulator is that the gauges come up more slowly when you start the car, but it has the advantage of internal thermal & current limiting.

I forgot to say that just isolating the ground of the gas gauge would leave the stock regulator trying to give all the gauges the full +12V; not a good idea. The ground is neccesary for the regulator to heat up and open it's points -otherwise, they'd always stay closed.

Life really is easier if you remove the cluster from the car - that usually isn't very hard. A couple of tricks really help:

1)disconnect the battery!!!
2) put the gear selector into 1 to move it out of the way
3)disconnecting the speedometer cable is usually the hardest part
4)if the ammeter nuts do not unscrew, do not use force or you will break the ammeter internally. Cut the leads off as close to the ammeter as possible, then later cut the nuts off using a Dremel tool w/ #409 bit or similar and crimp & solder new eyelets on the ammeter leads. I use Eastwood welding grease on the nuts to prevent them welding themselves in place again.

To slip a piece of heatshrink over the stud, you'd probably have to remove the gauge from the cluster 1st - I doubt you could force it in from the back easily.

W/o a similar cluster in front of me, I can't say which pin is which, but there ought to be a GND (maybe through the housing), a +IGN, a gas tank sender connection, and a regulator out to the other guages. W/o GND, the regulator points will stay closed and give +IGN to all the guages rather than the normal pulsing +12V on/off ~1Hz.

From you description of the TEMP gauge behavior, it sounds like that's what's happening. If you give >2X the voltage to the gauges, they should all read very high - you may have damaged them or the sensors already.

Follow the traces and it should be clear which one is which; again, that's easy w/ the cluster removed.

The internal regulator is a bimetalic strip wrapped with resistance wire to heat it; when it gets hot enough, the strip flexes, the points open, and the strip cools. If you add an external regulator and the points are closed, you'll be shorting the regulator to +IGN with unfortunate results and probably fry your gauges.

The senders are at about 10 ohms for full scale (HI/FULL) and 77 ohms for the bottom of the scale (LO/EMPTY) - you can use power resistors to check the calibration.

I recommend you remove the cluster and check each gauge and sensor carefully before you reinstall it.

okay, just to be clear... Does what you saying mean that this article http://www.slantsix.org/articles/instru ... nt_reg.htm does not fix the problem? Because it doesn't say anything about disabling the old IVR at all. Here I thought this was going to be easy.!

In the article, it says "with partially functioning gauges" (implied voltage regultor output very low), so adding the new regulator caused the existing regulator to always have it's points open once it warmed up. At initial startup, the LM7805 regulator would have it's +5V output shorted to +12V until the old regulator opened up its points and then they would stay open, allowing the LM7805 to do it's job.

Until the old regulator warmed up, the new regulator's output is shorted to +12V; fortunately, the LM7805 is current and thermal protected, so it could tolerate that for the ~15 sec or so it takes the old regulator to warm up and open its points.

So, if the old regulator has failed such that regulates (averages) way below +5V (on an average) or doesn't give anything, you can leave it alone, but if it's working around +5V or higher or is stuck full on, you'll have problems unless you disable it. I recommend disabling it in either case, as you never know when in might start to work again.

Got it. Thanks for your help. -MICHAEL

I am using the 7805 regulator on our 71. No problems with old internal regulators on a 71, but the gauges are slow and now read low by about 15%.

I just picked up some LM 350 regulators and am going to put an adjustable regulator together with one of these. They have a 3 amp output, which may just solve the problem itself. If not I can adjust up the voltage a little. I am going to put it in a small box with some easy way to connect a voltmeter and just run 8" - 12" of wire to the dash connections. This way I can get at it easy to adjust / calibrate it. The dash panel itself will not be modified.

Mounting it off board of the dash should make it easier. It will use a recycled cpu heatsink and a section of prototyping circuit board.

When I actually find the time to throw it together I will post some pictures.

The gauges were never all that accurate to start with; if you got them calibrated to 15%, I congradulate you!

You can use a Si diode to shift the LM7805 up and down by ~0.7V - in the ground leg will up the output, one on the output will drop it, but your adjustable regulator is a nicer way to go. If the gauges come up too slowly for you, you could gimick a time delay before the regulation comes on to emulate the ~10 sec of full voltage the stock regulators give - you can do that any number of ways.

The current limiting feature is good to protect the gauge if a sensor or wire gets shorted out.