I have never seen a Mustang with any kind of "resistant" wire before the CVR. The only "resistant" wire is the so-called Pink wire that runs from the ignition switch to the firewall connector to reduce the power going to the coil with the key in the ON position.

Yea it's there in the 71/73 harnesses that I have in the archives, (if it had the gauge package) . It's black insulated with one strand of silver wire. It has some #'s on It. I'm sure there's a name for it besides resister wire. So what I guess I'm asking, is anyone sure there CVR gets full voltage on the input side (loaded). It's disturbing as if one of any one gauge reads more [gas/temp or oil, the others will  lose some. The CVR can't make voltage if none is available, but I don't know what the limit is... 

Maybe the best plan is to just leave it alone like I tried the last 25yrs,  but on the other hand, I can't remember my original 72 mach doing that.

Last edited by red351 (4/29/2021 5:31 PM)

Rich, is it possible that the 71-73 NEVER had a CRV...just the fixed 5-6 volt resistor wire.  No appreciable load on instruments so once the engine is running the voltage across that wire should be fairly constant.  Personally...I would scrap it and go to adjustable solid state CVRs for each instrument.  That way, as Ron said, you can dial in each gauge.  As for the fuel gauge you may never get it to read F at full and E at empty.  They were never exceedingly linear and it you have an aftermarket sender.....well.....
If you want my method pm you email addy and I'll send some PDF's.  I just bought a dozen Won Hung Lo CVRs for like $11.00 on Azamon.

BB1
 

I thought about adding a relay controller as well to my insterment cluster this way I could add a dummy low Fuel Light. 

red351 wrote:

   Working under & inside a dashboard has never been my favorite pastime.
 
 

Nor mine...that's why I try to DIODIR.  I forgot about those "modern" mustangs having PC boards...fits right in today's political environment...and such.  I would do as you are thinking.  Connect the adjustable CVR from a 12v source (you could "cap off" the RX wire and just leave it).  I would pre-adjust the CVR to 5 or 6 volts before connecting it to the cluster as you don't know where that thing is set from the factory and you don't want to apply 12v directly to the instruments.  Then connect it, power it up and adjust it so the gas gauge is where you want it.  If possible you can use a separate CVR for each gauge which allows you to set them where you want when at normal temp running.  I like to adj. the gas gauge to be on the E mark with a couple of gallons remaining which may not let it go to the F when full...mine gets to about 7/8.
If you mount the CVR (s) on a small plastic panel off the bottom edge of the dash it takes a little more time but makes adjustment a lot easier. 
 

BobE wrote:

Suggest getting a wiring diagram for your year Mustang.  This should show this resistor wire, and/or the CVR unit.

No Bob it doesn't show or mention anything about that. That what kept messing me up. I would get a 12v at the input side of the CVR  till I connected all the gauges. It would drop to about 5v in & out.. I found the RW by accident opening up an old harness some time ago. I'm just getting around to maybe fix the problem.
 

Last edited by red351 (4/30/2021 10:26 AM)