74 Instrument Voltage Regulator

[Chiclassics]

Autobots!

I have been working on my new addition -74 bronco.
One of my shop guys did the electrical for me using painless harness from WH. He is not an expert but did 1-2 broncos before so kind of okay with electrical.

Only fuel gauge was working when I got from him. Temp was always full. and nothing on Oil pressure. So I went ahead and installed a new oil pressure gauge as the old one was not pegging at all when I grounded the sender wire. Now with new oil pressure gauge it started showing all the way to the high also. I started digging into other wiring around the cluster and realized he bypassed the instrument voltage regulator.

I now corrected it by connecting the terminals to IVR.

Now,
Oil pressure is showing 40-50PSI(once vehicle is at operating temp) - kind of close but still little high at idle ?, i think i should get no more than 30-40psi. Im using lucas break in oil SAE30
Temp fluctuates now all the way high or sometimes zero...before it was high all the time so some promise.
Fuel - still works same .

Now I figured voltage regulator bypass was the reason why oil pressure was showing all the way to high. Its better now but still not accurate.

Question is can my voltage regulator be semi-bad? giving wrong readings. is it a 12v straight pass through or is it stepping down

 

[Broncobowsher]

The IVR is stepped, but not stepped down. It blinks.
The IVR is just another thermal gauge core, but hooked to the power supply. Once it warms itself, it turns itself (and the other gauges) off. Then it cools and turns back on again. The higher the voltage, the quicker it warms, the more time it spends off and less on. As voltage drops, the contacts stay connected slightly longer to heat up the same amount. This makes for a fairly even average voltage to the gauges. Being thermal gauges, they are slow to respond. Way slower than a magnetic gauge.
The IVR has another party trick that many people overlook when they go for the modern solid state regulator. Temperature compensating. When it is really cold outside, the heaters that warm the bimetallic spring cool off faster, the gauge would read lower. But the IVR also being cooled faster will stay connected longer. so the gauges will work in the cold as well as they do in the heat. And summer in Phoenix, the IVR fixes that as well with less on cycle time to counter the hot enviroment. When they developed these gauges they were really smart! There is also the boost at key on as the IVR is cold and will stay powered a little longer until it comes to temp, which also brings the gauges to temp faster. You can often watch the IVR working as a gauge rises at key on, pauses or even drops a hair, then rises again and will eventually settle out.

With all that in mind, these gauges were never the greatest. It is best to just read them and use them to make trends. It's normally at 50, that is normal regardless of what it really is. That mark on the gauge is where normal is at. If it shifts from that, something changed.

The IVR typically has a little adjustment on it. It shifts ALL 3 gauges. I do my best to dial in the fuel gauge if I want to play with that. The other land where they land. They can go bad. Typically the contacts burn, or weld, or the heating element burns out. I had one on a BroncoII that was funny. Take an exit ramp off the highway and the water gauge would peg. But so would the fuel. Tap the gauges and they would settle back down. Never could figure that one out, never threw parts at it. You could tell what was going on, that was all that mattered.

 

[Chiclassics]

Ah didn't know so much goes on behind that little IVR. So i'll stay with it as is, as its showing 50PSI , and change my temp gauge and see if it at least stays at one spot instead of swinging from 0 to high every 3mins or so. Now I know my IVR works because its working well with my brand new oil pressure gauge...as same signal is sent to all 3 gauges.

My fuel gauge works which is most imp for me as well right now. Being a new engine I needed to monitor my oil pressure which works now so im good. Temp I can be ok without as i can tell if its overheating owning 12 or so classics got a pretty good sense of what a normal 190 feels like to touch. One time my willy's went to 230 i knew it right off the bat before my radiator vent spilled water all over when I came to a stop.

You can often watch the IVR working as a gauge rises at key on, pauses or even drops a hair, then rises again and will eventually settle out.

I did notice that ! a slight pause /hesitation before moving further...that means my IVR is good then.

The IVR is stepped, but not stepped down. It blinks.

What is the theory behind this. Why pulsed voltage?