Hi,

I replaced my ICVR a few weeks ago because I believed (and still do) that it had gone bad (may gas gauge needle bounced around sporadically and randomly). I removed my old one, plugged in the new one, screwed it back in place and started my truck. My gas gauge started creeping back up and things looked promising, but when it got to around 1/4 tank the needle fell back down and was never seen again. I was pretty sure I got a bad ICVR.

Called Mac's and they agreed, and sent me a new one. I'm going to put the new one in tonight, but is there any step in the install process I overlooked? In the box there is a note saying it must be grounded before being powered up. Is there any special meaning to that?

I just want to make sure I didn't screw something up and I want to avoid making the same mistake twice (if I did anything wrong).

Thanks!!

 

I have heard it is important to disconnect the battery when working behind the gauges. Very easy to fry the ICVR.

 

Interesting, I hadn't heard that. I installed the 2nd one the same way I installed the first and it didn't work either. Mac's was nice enough to replace the 1st one without any hesitation, but now they're saying the problem is with my truck, so they won't do it again (don't really blame them). But if it's a case of not having good instructions on how to replace it, that's a bummer.

 

There is no power going to the ICVR until you turn the key on so it's usually hard to screw it up when installing but always safer to disconnect the battery. The ICVR controls voltage to both the fuel gauge and Temp gauge. When it goes bad it will effect both. If you are having problems with only the gas gauge your problem may be else where, sending unit/float etc. Getting two bad ones isn't unheard of, most after market ones are cheap Chinese junk, I got three bad ones for a 66 Mustang..

 

The temp gauge is another issue, but the gas gauge was exhibiting textbook ICVR problems. The first one gave me a little false hope so I'm not sure what the deal is. I'm not sure where these were made, but they both had Mac's "tested" stickers on them.

 

I would check the ICVR's you have to see if they are good or bad. It is very easy to do.

All they do is step the voltage down from 12V to a pulsing 5V to power the gauges.

This will require some tools, an alligator lead, a decent analog VOM, (Volt Ohm Meter) and a 12V power source.

Test in exactly in this order.

Step 1
Put the VOM on the OHM setting and test for continuity between the Control terminal and the Ign terminal.

If there is no continuity (open) the unit is dead.
If it passes go on to step 2

Step 2
Check for continuity between the case and the ING terminal.
If none the unit is dead.

Step 3
Clip a lead to the ICVR case and the neg side of the power source.
set the VOM on DC volts and check for a pulsing 5V between the Control terminal
and the ICVR case

If it pulses to 5V it passes.

If it is high or low it can be adjusted with the set screw.

This is the procedure for the OE units.

I have not had one of these new off shore units apart and they may be electronic.
And this testing procedure may not work.

To me it sounds like you have short in the instrument cluster or a sending unit.

Hope this helps

Matthew

 

Thanks - this is exactly what I was looking for.

None of them have a set screw (the one that was on my truck nor the two replacements), but I will try this procedure anyway.

 

With out a set screw or post I would assume it is an aftermarket full electronic unit.

The only way I could see testing it would be to go to step 3 and see what you get.

The Ford units are all the same.

Part number B9MZ-10804-C Or new number GR-508 is for our trucks, Even the GR 508's are Electro Mechanical.

The others are identical internally just different connections externally.

C7SZ-10804-A Has Pin connectors.

D1AZ-10804-A has button connectors for plastic printed circuit boards.

All 3 do exactly the same thing.
So you can use any of the above, you just adapt to the connections on that particular unit.

Remember the ICVR case has to have a good ground where it is screwed down to or it will not function and could result in burning out the gauges.

There are still lots of electromechanical NOS and NORS available out there personally I would search one of them out and pass on the electronic units. The OE style can handle over loads and even shorts and does not care how it is hooked up power on or off. As all it has inside it are, a set of contacts, a bimetallic strip, and a chunk of resistance wire.

Hope this helps

Matthew

 

If you are still not where you want to be with these gauges, here are a couple pages from the shop manual.









Good luck in your quest!
Let us know what you figure out as it will help the next guy down the line.

 

Thanks guys! Hopefully I can play with it this week and make some progress. It hasn't been much of a priority since I have a lot of other stuff going on, but I need to get it done.

 

Hey Matthew,

I went through your steps 1-3 on one of my regulators last night. If I was doing things correctly, there was continuity between the terminals and the terminals and case. However, when I hooked it up to 12V (in a few configurations) I couldn't get a pulsing 5V anywhere. I saw 12V, 7V and 5V, depending on how it was connected, but none ever pulsed. Note: I did use a digital multimeter, which I'm now realizing might be my problem.

I also watched this: which shows the steps pretty well.

Any chance you know anything about the "7805" chip he mentions? He says they work better and are $2 from Radio Shack.

 

Yeah, digital multimeters average out the readings for the display. You need something with a needle for display.

 

This is an interesting subject. I checked out a few things and found that you can make a regulator to convert 12v to 5v using the 7805 chip and 2 capacitors from between 100 to 1000 micro farads. At radio shack that is about $2 each so $6 and a few wires/solder and a 5v regulator. Here is a link to the step by step Building the Regulator - How Electronic Gates Work
Now who will try it?