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I have a 65 mustang and the fuel and temperature gauges started reading inaccurately in the past few days. The fuel gauge says I only have a quarter tank but I just filled the tank and replaced the voltage regulator. I cant find the coolant sending unit to see if it's dirty or anything and i just haven't had the chance to look at the fuel unit. Thanks for the help.
Tracey
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I need some more information: Did you replace the instrument voltage regulator, or the one for the alternator?
What does the temperature gauge indicate? If you have the oil pressure gauge option, what does that read?
If all gauges are reading low, the problem is most likely the instrument voltage regulator. It has either failed or it is not wired correctly. A missing ground will cause this symptom.
Dick
I'm almost positive I replaced the instrument voltage regulator. The temperature gauge goes up when i first start the engine but settles back down to where it was when the ignition was off within a few seconds. I don't have an oil pressure gauge. When I installed the new voltage regulator I did exactly as the instructions said, and the instructions said it would be grounded by bolting it to the fender wall. Thanks for the reply and all the help.
Tracey
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No, if it is mounted under the hood, it is the main voltage regulator (which controls the charging of the battery).
There is another voltage regulator which provides the special 5 volt signal which powers your gauges. Since both of yours are acting up, I think that is probably the cause of your problem.
I do not have a wiring diagram for your car, so I cannot tell you where exactly the instrument regulator is, but I can tell you how to find it. You need to be quite limber, and have a good flashlight. Slither under the dash on your back with your flashlight (disconnect the battery first, to avoid shorting anything out with your flashlight) and look at the back of your fuel and temp gauges.
There will be at least two wires on terminals on each of the gauges. If one of the gauges has 3 or more wire terminals on it, the instrument regulator is inside that gauge (bad news - you can't get at it without destroying the gauge).
If both gauges have only two wire terminals, one of the wires goes to the sender (in the fuel tank or on the engine, for the fuel or temp, respectively). The other wire goes to the instrument regulator. Follow it and you will find it. Most likely, it will look like a tiny bathtub, with two or 3 wires no it.
One of those wires goes to 12 volts on the ignition switch, one goes to the gauges, as we just said, and the third one, if present, goes to ground. If you find it, make sure the ground wire is securely fastened, or if there is no ground wire, make sure the metal mounting tab of the device is securely grounded to it's mounting point. Clean the mating metal parts to make sure.
This may cure your problem. If not, get a volt meter or a test light, and probe the wire which runs from the device to the gauges. You should see a pulsating voltage (or a blinking light if you use a test light) blinking about once per second or so (this is not critical, if it is blinking, it is OK). Of course, the battery has to be hooked up for this and the ignition key on. The engine doesn't have to be running, just turn the key on.
Back up now: If you determined that the instrument regulator is inside one of the gauges, probe the wires on that gauge to see if you can find the pulsating voltage (or blinking light on your test light). If you can, the instrument regulator is probably all right, and your problem is elsewhere. Don't go to the expense of replacing it until you know it is bad.
I'll stop typing now and let you respond to me with what you find out. If this hasn't led you to the problem, I'll try harder.
Dick
I did find the regulator and luckily it isn't in one of the gauges . I cleaned it up hoping the ground was dirty but no luck. I don't have a tester so I'll have to wait till Friday to get access to one. I'll let you know. Thanks for all of the help.
Tracey
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OK, good, go ahead and check it to see if it is working. If not, NAPA still carries these -They call them instrument regulators. The right one for your car is an ECHLIN IR1, I beleive.
Let me know how you make out, please.
Dick
I checked the regulator with a meter and it turned out to be pulsing three or four times a second. So I went to NAPA and got a new regulator and it acted weird for about ten or so minutes. It went up then down and back up and back down but eventually started working fine. So my problem is no more. Thanks for the help.
Tracey
AnswerOk, Great; I guess we tracked it down to the right cause.
That rapid pulsing sometimes is a symptom of momentary contact of one of the sender wires with ground - so if the symptom returns, inspect both the fuel and temp sender wires for contact with bare metal somewhere along their run. Hopefully, this is a permanent cure, but just in case it comes back, you'll know what to look for.
Dick
