View Full Version : Speedometer cable

06-02-2014, 01:52 PM
I worked on the ranchero over the weekend and got the new rear leaf shackles and bushings in but now I notice the speedometer has quit working. It appears that the end has come off and the cable is broken somewhere in the line.

How difficult is it to put a new one in and are there any things to watch out for? It is a 4 speed V8.

06-02-2014, 10:31 PM
Speedo cable is pretty easy. Just have small hands and be a contorsionist. The hardest part is reaching up under the dash to screw or un screw it from the gauge cluster. The trans end should have a small clip with one bolt holding it on. Undo that and pull straight out and it should come right out.
Go for it, you should have no troubles.

06-02-2014, 11:04 PM
Hey, thanks so much for the info.

I bought a new cable and C-clip; the cable has an attached kind of holder with a hole in it and 4"cushion piece around the cable. The end for the dash has a round nut and the tranny end has a push-in fitting with an 'O' do they come pre-lubed or should I add some?

06-02-2014, 11:27 PM
Wouldn't hurt to put a touch if gear lube on the "o" ring. If it was an auto use trans fluid.

06-03-2014, 09:26 AM
Speedo Cables, if new, are probably pre-lubed, but it never hurts to pull the cable out of the housing and check. Cables are lubed with a special grafite-based lubricant that you can find at most good auto stores, or online. In a pinch you can use Lock-ease, which is graphite based spray to help carry the lube down the housing. And as Steve said, a light film of oil on the o-ring.

06-04-2014, 03:06 PM
Thank you so much for your info, I really like this forum

Tom :)

06-05-2014, 09:02 PM
I just replaced my speedo cable yesterday. The actual installation of the cable is a snap. Mine is pretty difficult because the cross member on the frame is right adjacent to the outlet on the Tremec transmission for the cable. The cable routes through the frame for a distance and exits through the bottom of the frame.

I originally ground out a section of the frame and thought is was okay, but I noticed a small leak around the speedo at the tranny and saw that when I lowered the tranny onto the support it bent the speedo housing and was causing it to leak around the o'ring.

I replaced the cable, ground out the hole quite a bit larger and it clears now. Don't let that scare you about installing a new cable. The actual cable install only takes 20 or so minutes. Larry

06-09-2014, 02:50 PM
My plan was to replace the speedometer cable but in the course of several days here is what happened.

I stopped at the store and when I started up again I noticed that the temp. gauge was not working nor the fuel gage. Went online and ordered the newer style constant voltage regulator. I thought I'd just put that in along with the speedometer cable and just get into the dash once, also bought some new dash lights. Well, before the part came in the turn signals went out, meaning no blinking dash lights or blinkers outside.

So today I put in new speedo cable, all new dash lights, cv regulator and a new flasher.

Guess what the fuel and temp still don't work nor do the turn signals!?

Here's what seems odd-
Headlights work, stop lights/tail lights work, dash lights work and dim, horn works, gen and oil lights work.

:doh: What is going on here?

06-09-2014, 03:03 PM
GROUNDS. Check all your grounds. Your fuel tank actually ground from being mounted to the frame. I usually run a second wire from the tank to the frame and ground it that way. As far as your temp, make sure the connection on the intake is good. Also check the ohms reading, it may have just gone bad. Mine just did so new sensor fixed mine. [thumb]

06-09-2014, 04:03 PM
I did a quick scour of the wiring diagram to see if there is a common source for these failures, and not really finding one. The headlight switch on this car is the source of power to many things because the fuses are built onto it. Some power comes from within the switch, where a couple others get their +12 volt feed sent to and then out of the switch harness, but are not sourced from within the switch. For instance the flasher +12 volts is fed from the headlight switch, whereas one of the Black w/Green feeds from the IGN switch goes to the headlight switch (to power the switch) but also connects through a fuse to the Heater brown wire.

For now, key on, check the fuses on the headlight switch for 12 volts on each side of the fuses. Check +12 volts to the Black w/Green wire on the CV regulator. Check +12 volts to Yellow/Black on flasher.

I tend to think along the line with Steve these may be coincidental failures, but I sure can't see a single ground causing all of them, nor a single source of power failure either. Each are on a separate source.

All of this, of course, assumes nobody in the past 50 years as messed with any of the factory wiring. :ROTFLMAO:

06-09-2014, 07:18 PM
Thank you both for the replies-

I don't believe both are related either just that both happened so close together. I think I will work on the last that occurred and it may be solved at the switch with fuses (I hope).

I was figuring that the fuel and temp gauges would be solved with the new (they say improved transistor type) constant voltage regulator from Falcon Parts though. It's a real pain trying to do any kind of work on the dash and related wiring.

Any other thoughts or ideas would be appreciated,


06-09-2014, 09:58 PM
There's a pretty decent test document on FalconParts.com for testing the dash gauges just to see if it's the sensors or not. It's on this page, which I'm posting the entire page rather than just the link to the page, since there may be other links you or others may not have seen before on this page:


Good luck!

06-10-2014, 12:13 PM
I decided to take a ride this morning and do some errands and maybe work on the car later. Made my first stop and after I started up the fuel and temp. gauges started working as usual. Made several more stops and things seemed just fine, the 2 gauges were working like usual.

I decided to try the turn signals and low and behold both gauges started falling to zero and not working again right before my eyes. Trying to move the turn lever around a little didn't get any response.


06-10-2014, 12:27 PM
I have thoughts, but not sure you believe in that sort of thing or not, so I'll keep those thoughts to myself. :WHATTHE:

Could be an intermittent key switch, but other accessories tied to those terminals would also be failing. So... there is nothing else you can find failing? You have tried the heater, radio, door lights, etc. etc.? I'll study the diagram again and see if I have an epiphany.

06-10-2014, 09:07 PM
Are you saying maybe some Gremlins in the Falcon? [AGREE]

Sure seems to be something shorting that connection when I turn the blinkers on!

I really thought maybe it would just be a fuse for the blinkers though.
It does kind of eliminate a lot of things though- CVR, Fuse, Bad Gauges and sending units.

It's beginning to sound more like a short, rubbed wire etc. but I don't understand the connection between two seemingly unrelated circuits?

I really appreciate you trying to help me solve this,

06-10-2014, 10:23 PM
I've been talking this through in my head for about an hour now and yes they do have a common circuit. Turn signal goes on and sends power up to the gauge cluster to activate the turn signal indicator, could a bad GROUND be our common denominator? If the ground for the gauge cluster is not very good it might work a bit till it gets loaded up with several things being on and stop working?
Like I said I've been talking in my head so this might still be in my head and I'm not really typing this???:D

06-11-2014, 09:00 AM
So you're thinking the ground for the cluster? Is there a separate one or is it just the screws holding it to the dash it self?

Dash lights work, oil and gen lights work, headlights work, taillights work but turn lights do not come on in dash or at corner lights at all.

When the fuel and temp. gauges worked yesterday nothing else was on but as soon as I moved the turn signal lever both gauges started for zero immediately. I turned the car off and restarted several times yesterday and the gauges worked fine every time but never tried the turn signals til I was idling in the drive way at the end!

06-11-2014, 02:03 PM
I've been staring at the diagram (see attached) and there is only one thing common. I'm beginning to lean heavily to it being a voltage drop coming from a failure at the ignition switch.

From the ignition switch there are two sources to feed things - IGN and ACC. There is a feed directly from the battery (solenoid) BLK-YEL to the headlight switch, but it seems to power headlights, door lights, and the stop light switch (all of these are key-off ready).

If you look at the diagram the headlight switch gets a feed from the BLK-GRN from the center ACC switch terminal. This also provides power to the other fuse on the headlight switch to feed the ORG-YEL (turn signal flasher) and BLK-RED (backup light).

The CVR also gets its power (unfused) from the ACC terminal of the IGN switch.

So here we have the only common connection between the BLK-GRN to the CVR and the BLK-GRN that feeds the headlight switch, and through the fuse to the ORG-YEL to feed the +12v to the flasher. I think when you use your turn signals there is a voltage drop to the CVR and the gauges no longer can function.

So check the tightness of the nut on that center terminal of the switch, and failing that being loose, I think it is the IGN switch internally.

06-11-2014, 02:32 PM
Also, for what it's worth, I've used the new CVR's and they work fine. The gauges run on about 5-6 volts and the way they did this in the olden days was to use a bimetallic regulator sort of thing. There was a wire wound around a bimetallic spring inside these and when 12 volts was supplied to that winding (cold) it would heat the thing up. It would quickly heat the spring, bend it, and the current feed would then get broken. Then the spring would cool, close the switch, and heat up again. Rinse and repeat.

The dwell time between the on and off (this was adjusted at time of manufacture by increasing or decreasing pressure against the spring contacts, then "glued in place" with some sort of fingernail polish) created an appearance of there being about 5 volts (0-10v swing).

The new units use a true 5-6 volt regulator. I discussed this in a thread sometime last year and even bought parts to make some of these myself. I have not got aroundtuit, but have enough cans and parts to make about a dozen of them. Real Soon Now.

06-11-2014, 03:40 PM
You know I thought about the ignition switch but I also thought once I turned the turn signal off the gauges should have worked again but got nothing.

I also tried turning the key to the ACC side to see if they would power up but still nothing. :doh:

It may take some time to figure this one out and may have to wait til I come back from vacation.

I'll keep you all posted and try to look into the ignition switch.

If you can think of any thing please let me know,


06-12-2014, 10:11 AM
Other than to check voltages at the time of failure, this is all I can come up with.

I've created every wiring harness, from scratch, for almost ever car I've built (which is hardly Painless :D ). There is not a lot of magic here, but it does cause a lot of people a lot of anguish. I have 4 tubs of wiring harness bits and pieces just for that reason.


Bottom-line is you just got to get out the old voltmeter and see what is, at the time it isn't, and know where to look. If voltage isn't at the time it isn't, where isn't it coming from where it should be coming from?

I'm sure that made total sense.


06-27-2014, 04:48 PM
Been on vacation for a couple of weeks, just got back and thought I'd start trying to find the source of the electrical problem. Went out and put the key in the ignition turned the key to on and the fuel and temp gauge worked just fine!

Turned the turn signal on and the fuel gage started for zero, tuned the signal off and nothing, turned the ignition off and back on--the gauges came alive again. Did this a couple of times and now both gauges don't work again.

I took off the steering wheel and checked turn signal connections and all seems fine but the gauges still don't work. I guess I'll dig into the dash wiring next!

After checking a little more though I have head lights, horn, running lights in rear and stop lights, all dash lights, oil and gen lights but-- no parking lights in front, no turn signals front or rear and no turn indicator lights in dash.(and the temp and fuel don't work)

If anyone has any miraculous thoughts or epiphanies please let me know, otherwise it may be a long summer.

06-30-2014, 05:31 PM
[yay]This seems like a good news and bad situation, on one side it seems I have found the area causing the problem but I not sure how to handle it now!

I spent most of the day today trying to locate the problem with my turn signals and have narrowed it to the ignition switch.

There are 2 wires(from a previous owner) connected to the screw in the center of the back of the ignition switch. The wires are not connected to anything else but are connected to this screw so they must have gone to something somewhere along the line. When I move either one of these wires the fuel and temp gages go to zero. If I move them around again the gages come to life. One of wires is substantial size and the other has one side of a fused connection on it.

My questions are-
Is this screw hot or is there something else going on behind the wiring cover?

How is this effecting the turn signals?

Should I just order a new switch and wiring cover?


06-30-2014, 06:30 PM
Switch post should only be hot with key on.

My guess there is a short in the ignition switch pig tail.
You can replace (or used to) the pig tail, but it means cutting and splicing wires. Not a problem, if you know how to do it correctly. Crimp and butt connectors could cause problems in future.

Option 2 replace under dash wiring harness..

06-30-2014, 08:57 PM
That explains a lot about the post and the wires. I was thinking just replace the pigtail and the switch but, do you think it's worth removing the wires from the post and see if things clear up?

Why do you think the turn signals are involved though and now I noticed that in trying out other scenarios when I turn the heater fan switch on the fuel and temp gauges act the same as when you turn the turn signals on!?

06-30-2014, 10:20 PM
That center screw is the aforementioned ACC (accessory) terminal (see my post above, #18). This terminal goes hot when in the run position and feeds everything you are mentioning failing. It is also the terminal others hook things to as they add... accessories.

This was the terminal I suggested to focus on, but if these 'extra wires' really go nowhere, and are left-overs from some previous 8-track player or something, disconnect the negative BAT terminal under the hood, remove the nut on this center terminal - and yank the unused wires. If these wires are grounding out, and they are hot - they will possible become an unwelcome light bulb. You may also simply find this center nut is loose, which would be causing the problem as well.

You're close...

06-30-2014, 10:25 PM
Why do you think the turn signals are involved though and now I noticed that in trying out other scenarios when I turn the heater fan switch on the fuel and temp gauges act the same as when you turn the turn signals on!?

These all feed off that center ACC screw. If the internal part if the switch, or just the nut on that center terminal is loose... a voltage drop due to high resistance will effect everything running off that circuit.

07-02-2014, 06:04 PM
I know it seems like it all narrows down to that center post and things attached to it.

I'll get some time to work on it tomorrow and over the long weekend. I think I will try to eliminate the obvious; not needed wires and tighten things up first.

Worst scenario is a new ignition and pigtail it seems. It is such a pain working behind and under the dash, no room and dim lights!

Thanks to all, the end seems in sight. [thumb]

07-02-2014, 07:31 PM
Though it seems like a pain, if I've got more than an hour or two worth of work under the dash I take 5 minutes to remove the seat. Mines a bench so I call the neighbor to help but only 4 nuts to remove and you've got a comfy spot to lay on your back and work.

My back starts to growl if I cram myself between the seat and steering wheel for too long! :mad:

07-02-2014, 09:42 PM

working under the dash isn't that bad when laying on your back on the floor..
Just wear safety glasses.. there's years of crap up under them dashes.

07-09-2014, 02:28 PM
:banana:Success finally!

All of the trouble centered around that darn center post. I took the wires off that didn't really seem to go anywhere and put the nut on but things still didn't seem to work. Then I remembered I was told to tighten the center nut tight so I went back in and tightened it up. Put the cables back on and everything works perfectly, gauges and signals.

Thank you all so much for walking me through the process.