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Discussion Starter #1
Hi all, On my '66, I find when I pull out the light switch, to either parking lights, or full on lights,
the instruments controlled by the IVR go up, ie, the fuel guage reads higher by almost a full
increment, the oil pressure goes up by almost a full letter and of course the temp guage goes up
by almost a full letter. Turning the lights out brings the guages back to normal. The IVR is a
fairly new solid state unit.

I measured the ivr output at 5.1 volts with the lights off and almost 6 volts with the lights on.
I tried a different light switch (used) but same results. I don't think its the ivr because I
believe it's a symptom of the problem and reacting to the cause. Or, maybe it's the cause?
Studying the wiring diagram, I just can't see a connection between the light switch and ivr
output.
Any ideas?
 

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Has a PO messed with the wiring behind the dash and possibly wired something incorrectly? Does it do this with the engine running? Maybe turning the lights ON causes the alternator to "kick into high gear" putting out more voltage?
Maybe the new solid state IVR is defective. Have you tried replacing it with an original?
 

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Discussion Starter #3
Does it with both engine running or not. Wiring has not been messed with, very stock. I am leaning toward the ivr but I want to find an original, ie, points type first. I've put in new, solid state ivrs in other cars I have and not really had
good luck, kind of hit or miss on the quality.
But I would think the if the alternator were to 'kick into high gear', the ivr should still control its output.
Thanks.
 

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I don't believe its the IVR. They are separate circuits and do not connect in any way EXCEPT for power.
They share some common wiring up to a splice: Power comes from the battery on wire 37 black/yellow stripe, through the firewall plug and to a splice where four wires splice together. At this point they diverge. 37 black/yellow, 21 yellow, 25 black/orange, and 37 black/yellow. 21 yellow eventually goes to the gauges and 25 black/orange goes to the light switch. The others go to circuits you aren't concerned with. It sounds like you may have a bad connection at the firewall plug or a bad splice. I would bet on the firewall plug.
BTW, putting in an electronic IVR could solve the gauge problem, because an electronic version will regulate to 5v as long as the voltage to it is above a certain threshold, unlike the stock IVR. But that won't solve the real problem if unwanted resistance is at the firewall plug or possibly the splice.
Another consideration- some people have noticed that an electronic IVR will cause about a 30 second delay in an accurate display of oil pressure at start-up, and those of us with very expensive engines don't want to wait that long. Can't blame them.
 

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Discussion Starter #5
Well, I would have never guessed it either but it was the ivr. Pictured is the culprit, the installed one with the
green 'face'; letters in the lower right corner stand for Scott Drake? I don't remember where I got it
but the one pictured with the white face is the one I replaced it with.

Thanks everyone for your input!
 

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Well, I would have never guessed it either but it was the ivr. Pictured is the culprit, the installed one with the
green 'face'; letters in the lower right corner stand for Scott Drake? I don't remember where I got it
but the one pictured with the white face is the one I replaced it with.
It looks like a Daniel Carpenter 10814-1EA sold by NPD, and if so, it is electronic, and as I said earlier, it is probably masking the real problem with high resistance in the firewall plug. If the plug is the real problem it will eventually fail and you will loose power to all sorts of things. Just out of curiosity, have you noticed how long it takes for the gauges to get up to operating range? I'd like to verify that the electronic IVR does in fact slow down response time. It makes sense that it would, but there is no need to bore you with a lengthy explanation unless you're interested.
 

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Discussion Starter #7
Well, I think you're exactly right and I'm sure I'm only fixing the symptom(s). I'll go over my firewall plugs. It does
take a long time, maybe 40 seconds or so, for the gauges to get to their operating range
 

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It does take a long time, maybe 40 seconds or so, for the gauges to get to their operating range
From my experience, that indicates it is a digital regulator. They put out 5v constantly. Analog ones put out 12v/0v so that they read in about 5 seconds, not 30+.

I'm sure there are people who are really smart with electronics that can make a digital one put out 12v first and then 5v later, to better mimic the analog ones. I'm not in that category, to say the least.
 

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From my experience, that indicates it is a digital regulator. They put out 5v constantly. Analog ones put out 12v/0v so that they read in about 5 seconds, not 30+.

I'm sure there are people who are really smart with electronics that can make a digital one put out 12v first and then 5v later, to better mimic the analog ones. I'm not in that category, to say the least.
Yes, a technically competent person could easily design a better device, and there are many different ways to do it economically. Its unfortunate that the people who make the electronic IVRs are probably unaware of this shortcoming. I have no dog in the fight, since I'll be switching to Dakota Digital's retro tech.
 

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From my experience, that indicates it is a digital regulator. They put out 5v constantly. Analog ones put out 12v/0v so that they read in about 5 seconds, not 30+.

I'm sure there are people who are really smart with electronics that can make a digital one put out 12v first and then 5v later, to better mimic the analog ones. I'm not in that category, to say the least.
There is no need to "mimic" the analog IVR. The cyclical "on/off" action is designed to average an output of 5 VDC. Whether the gauges are supplied with a constant 5 VDC or cyclical average makes no difference as the cycle occurs faster than the gauge can respond, since the gauge works off a bi-metal strip heated by a resistor.
 

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I've heard more issues with Scott Drake items. In addition to this IVR, was an issue with the rag joint steering coupler for my 71 having safety pins that were too short. It shouldnt have even been sold.
 

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There is no need to "mimic" the analog IVR. The cyclical "on/off" action is designed to average an output of 5 VDC. Whether the gauges are supplied with a constant 5 VDC or cyclical average makes no difference as the cycle occurs faster than the gauge can respond, since the gauge works off a bi-metal strip heated by a resistor.
I agree that the overall results are the same, but when I did a swap, the digital cause the initial sweep of the needle to take about 30 seconds whereas the analog's initial sweep takes about 5 seconds. I don't understand electrics and electronics, but I thought I recall someone on this forum explaining that it was because the bi-metal strip starts out cool and takes a few seconds to warm up before cycling.

From your experience, did you get a ~5 second sweep with the digital regulator, or was it a slower sweep? I wonder if it is my particular setup or just how it works.
 

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Discussion Starter #13
I think your question is directed to Woodchuck, but I found there is no sweep with an electronic ivr. It simply
puts out 5v and the gauges respond, albeit slowly, to where they should be.
 
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