IVR

How are you measuring it? Your measurements suggest the IVR is stuck on. If that were the case, it is likely both the temp and fuel gauges are pinned at full scale most of the time.

The IVR is basically an on-off switch. When on, the output is at 12V. When off, it's at 0V. It typically oscillates at about 2 cycles per second. Depending upon your measurement technique, results can vary, but you will never see 5V on the output; that is an average based on the duty cycle.

Mr AMX wrote: Would it be correct to have the IVR 12v instrument panel pin wired to the fuse panel, 10a fuse, switched?

Don't have my manual handy, but I think it runs of a 4A fuse, the smallest fuse on the fuse panel.

An IVR is a very crude way of regulating. I changed to a solid state regulator long time ago. First one piece but it didn't held up in warm weather. They get warmer the more current they have to deliver and the more volts they have to drop and stop working when too hot. They resume once cooled down. I than used one for each gauge (a bit of trace cutting and some extra litlle wires involved) and that has been reliable since. They just get warm now, not hot.

Peter Jan wrote: An IVR is a very crude way of regulating. I changed to a solid state regulator long time ago. First one piece but it didn't held up in warm weather. They get warmer the more current they have to deliver and the more volts they have to drop and stop working when too hot. They resume once cooled down.

The solid state IVRs that use a linear regulator (typically the 7805 3 pin regulator) will get hot because they are very inefficient. The designs using switching regulators are much better, stay cooler, but are more complex.

The instrument regulator is kind of misleading description. It's not a regulator in the common sense of the word. A true regulator will keep a constant voltage on it's output. What the instrument regulator does is pulse the battery voltage by opening and closing contacts. If you take one apart you'll see there is a heating element wound around a bi-metallic strip. It will deflect when heated, which opens the contacts. This stops current flowing through the element allowing the bi-metallic strip to cool, which closes the contacts again. This cycle happens over and over at a rate of about once or twice per second.

The good thing about that is if there's an overload condition (too little resistance) the time the contacts are closed is extremely short because the element will get hotter and cause more immediate and longer deflection.

Using a true voltage regulator, either liner or switching, is a mistake. If there is an overload condition these regulators will supply as much current as they are designed for which could cause wiring damage.

-Steve-

Maybe I should use the Radio Shack 7805 as a tester. If it works, then purchase the solid state. If it doesn't, then I only lost a couple of bucks and gained yet another issue...or question.