OK, let me put a different perspective on the IVA and its possible implications. Most of us here (me included) have experienced the infamous IVR gauge issue. I am not trying to talk down to anyone here, just an explanation is a different manner.......
I know for certain on the 80-86 F Series trucks (80-86 gassers and 83-86 diesels (diesels were introduced in the 83 model year, along one minor exterior change, in 83 the "blue oval" was first placed in the center of the grill, in 80-82 F O R D was spelled out across the hood, similar to the earlier trucks)) and in the 80-92 (I think 92 was the last year of the 73 on van body, yes they ran the same basic van body for almost 20 years with various minor face lifts, round to square headlights, move the location of the Econoline name etc).. sorry back on target.
On the back of the instrument cluster, there is a silver box, about the size of a cigarette pack if I remember right (been a while since I have had an 80's era dash apart). It cycles on an off, limiting the amount of power to the instrument cluster. I think it is a 50% cycle, so in essence, when ever the instrument cluster has power applied to it (key in the run position) the gauges themselves are receiving an on-off of applied power to it. If the key is on for an hour, the instrument has only gotten power for the equivalent of 1/2 an hour. It is a simple relay type circuit (think turn signal flasher) on-off-on-off.......... when the instrument cluster is receiving this correct signal, all the gauges should read "normally" (please do not start the factory vs aftermarket "real" gauges debate, that is not where this is going. Personally, I understand the purpose and design intent of the factory instrumentation, I do not like the 87+ oil pressure setup, but again this is not where this is going) I do not have a problem with the factory gauges as they do tell me useful information, I have driven vehicles with "real" gauges, and after the first few times I look at them I do not care what the #'s are, I look a the needle position, as long as they are where I expect them to point, that is all I need to know when running down the road) for this example, with the trucks and vans that I have personal experience with (the most with a 83 F-150 and an 85 E-150 with this same gauge setup), the Temperature gauge would normally point between the "O" and the "R", oil pressure would normally be in about the same location (remember the 86 and earlier does have a real pressure sender that moved the needle in accordance with the oil pressure, with the introduction of the "bricknose" in 87 it is a on-off pressure switch, when the pressure switch has at least 7psi of oil pressure, it will send the needle to the middle of the gauge, my 03 6.0 is still this same system.) The above location is at normal operating temperature, cruising at a steady 55ish speed. I, as I believe most people, keep an eye on the Engine Temperature gauge more ofter than the other gauges. If the IVR is working correctly, all is good, and the above readings are maintained. If the IVR malfunctions and from what I have seen personally and read on the forum is it malfunctions and stick in the ON position, not the OFF position, which is now giving the instrument cluster power 100% of the time rather than the expected 50%. The first we experienced this we thought we had a thermostat issue, and as did Mel, we replaced the thermostat and the problem went away. (It didn't actually go away, the IVR started working again on the next start-up.) However, a few days later, same thing, it was running "hot" again. This time we noticed something else, the Oil Pressure, Ammeter, Fuel and Temp gauges were running high. (We had filled the fuel tanks, and the fuel gauge was almost hidden behind the cluster on the full side). We had a "wait a minute" moment and realized something was going on. We live in the country and the roads are not the smoothest, we hit a chuck-hole, and all the gauges went back to their "normal" locations. This happened on and off all the time. We bought the 85 van, and the gauges did the exact same thing. I honestly did not know, until a few years ago,after I joined this forum, that this problem had a fix. For all these years, Dad and I had just chalked it up to "typical Ford gauges". It can be quite a surprise the first few times it happens.
All, one other thing to remember: There are many of us that have been around these era of trucks and are used to their quirks. There are many members that join this forum, and these are "new" to them, and are not used to all the quirks and personalities of the trucks. I am fortunate in the fact that I have been a motorhead since I was very young, and Dad and I did most of the work on his and my vehicles and other "stuff" over the years, so even before I was able to drive I was familiar with vehicles and repairing them. I am sure that with some of the members and these trucks, the truck is older than the owner. I know there are many of us that remember when these trucks were new on the showroom floor (myself included) and was there when these same problems were new to us, just 20+ years ago....... and we were just a stumped as the guys are that has the first experience with these, now..........
Looks kinda intresting as to what they are for...
bad idea as the shock can stress/crack things.
. told ya so 
just stirring the pot
