Hi. I am doing a ground up resto of a 74F250 4wd; I have spent 11yrs working on this project off and on. I have rebuilt, replaced, or fabricated every component and system on this truck. Right now I am rewiring with a Ron Francis Street Rod wiring kit. My problem is to intigrate the original dash into the harness I cut the wires coming from the 18pin connector that power the dash lights, turn signal lights, & dash gauges ect. unfortunatly one of the wires I cut, the one that provides the power to the gauges reads "resistor do not cut or splice". I guess it is a resistor wire that drops the voltage for the gauges to the correct amount. I don't have the rest of the harness any more, like an idiot I cut off all the connectors I thought I might need and tossed the rest. I have no idea how long this wire was supposed to be or the correct voltage for the gauges, 3 volts? I don't know I am just guessing I noticed while looking at the schematics for the 75 and later trucks that they used an item called a "constant voltage supply" to provide power to the gauges; would this work on my gauges? I called Ron Francis, they weren't much help. Looks like I will have to go junk yarding again... I have also considered going to an electronics supply house and trying to come up with some kind of device, circuit, or component that would drop the voltage to the correct amount but I am not sure what that would be, any one know? What amperage should I plan for? Less than an amp is my guess. I realize most of the posts here are more of a nuts & bolts nature but any suggestions would be appreciated.

 

I recently had the resistor wire for the ignition circuit burn up on my 73 F250. What a mess, it burnt up a large chunk of wire harness behind the dash. Anyway what I did was repair/replace all the burnt wiring. Then I removed all the resistor wire and replaced it with a proper sized ballast resistor to drop the voltage down to the required amount.
You could do the same for your dash guages, if you can find out what size you need. The way I did mine was to get a wiring schematic for the truck and it showed the resistance value of the resistor wire. Then armed with this knowledge I found a ballast resitor of the correct size at the local parts store.
Oh if you decide to go this route mount the resistor where it can get rid of the heat it produces, dont hide it in a wire bundle. I mounted mine under the hood on the drivers side fender.
Hope this helps out.

 

Hey Jeff.
The wire you cut has nothing to do with the gauges in the dash. that voltage is regulated by the C.V.R or constant voltage regulator. It snaps to the printed circut strip on the panel back like a nine volt battey The wire you mention is the ignition coil resistor wire. It is a premeasured length of wire having a calibrated resistance. It drops 12 volt to six volt to keep from burning up the coil. This wire is almost like rubber in texture and approx 60 (thats right) sixty inches long, and is spliced between the ign switch & coil lead. Email me if you need more info.

 

D. Bellis is right, I have had problems with the
resistor wire befor and have pulled them from
wireing harnesses at the salvage yard. Any 70s
ford with Dura Spark will have what you need.

Good luck with your truck!!

Bill F.

 

Thanks for the advice but why is this wire coming from the rear of my dash if it feeds the coil? It would make sense if it went from the ign swtch to the coil... Also when i follow the printed circuit tape on the back of the dash it leads to the gauges and when I power this wire with 12volts and ground the sending unitwires the gauges operate albet they peg themselves though...

Another question I converted from points to the ford duraspark ignition do I need to use a resistor on the coil or not? I am at the moment and it seems to run just fine but I have been told it was only needed on points systems to keep from burning up the points.. I thought it was to protect the coil. Thanks for the help.

 

Thanks for the info it seems kinda odd that this wire exits the rear of my dash if it feeds the coil... wish I had kept my old harness so I could have chased it down oh well back to the junkyard and I thout I was past that stage of this project....

 

You have to have that resistor wire whether you have points, or duraspark, period. elimination of that wire will mean eventual elimination of the stock ford coil(about 100 miles or less)! As to the gauge problem I'm not there to see exactly what's going on, but I know for sure that the only "pink" wire that is marked "resistor wire do not cut", is for the circut going to the positive, or "batt" terminal on that coil. On the gauges you should have 12 volts to the instrument voltage regulator. From there the voltage will sort of "pulse" off and on to the gauges. If you will hook a 12 volt test light to the output side of the I.V.R. you will see this. It won't be very bright either, as this voltage drop is done so as not to burn out the stock Ford gauges, and from the gauges to ground, via the various sending units. Ever wonder why they are slow to respond, this is why. That I.V.R. is what runs the gauges. If you have any questions email.