Factory Tac and fuel gauge not working

[vintageman]

Good evening everyone, I started my car today for a maiden drive and found that the factory tac was not working. I am running a Duralast distributor with points and coil from a local auto parts store. I only have the distributor and gauge harness connected to the coil. Also noticed that the fuel gauge was in-op as well. I have about 10 gallons of fuel in the tank. My center stack gauges (oil, alternator and temp) all work. Did not take it for the drive, so not sure about the speedometer yet. Any thoughts and assistance is greatly appreciated. Thanks.

Tom

 

[Don C]

Is this the first time you have started the engine? If not, did the tachometer work the last time you had it running? Did you change any of the wiring when you installed the new distributor? Does the wire that runs from the ignition switch to the coil appear to be the original wire (red with light green stripe)?

 

[vintageman]

Thanks for the response Don. Yes, first time starting the engine in the car. Other times were on a run stand. I did not have a gauge harness with the engine harness, so I purchased one from NPD last year. No other changes to harness. Thanks.

Tom

 

[Hemikiller]

Smack the top of the dash a couple times. I've had the factory tachs stick after sitting.

For the fuel gauge, pull the connector off the tank sender and jump the two wires together. The gauge should go to full. If not, check continuity to ground on the black, and voltage on the yellow with white.

 

[vintageman]

Thanks Hemi, will give it a try when I get home tonight to work on it. May have to wait till the sun goes down, it's like 90+ degrees outside here now. More to follow.

Tom

 

[vintageman]

Thanks again for the advice. I did not get a chance last night to look at the car, got home from work later than normal but will be able to look at it tonight and report back with any findings. More to follow.

Tom

 

[vintageman]

Did not try to start it tonight, I wanted to check the fuel gauge issue as HemiKiller suggested, I jumped the two pins and checked the gauge, no change, fuel gauge stayed at empty. I tested for voltage at the yellow and white wire, nothing. Disconnected the harness at the door sill from the other harness and tested for voltage at the plug, nothing. Checked all fuses and they are good. Any ideas and thoughts for what to check next? How much voltage should I get at the the sender unit, can I run a switched wire back there to test the sender and gauge? Thanks for any and all advice.

Tom

 

[JJU9507]

Check continuity front to back for sending wires I believe there is a connector hiding behind driver lower kick panel.

 

[vintageman]

Thanks JJU, you may have missed my earlier post, I am not getting power coming from the plug at the kick panel coming into the rear harness. Any thoughts on what to check? Thanks.

Tom

 

[Hemikiller]

You should be getting 5V at the fuel sender wire, but it will pulse. Some meters may not pick it up. Use a test light and see if the bulb illuminates. If not, then I'd start looking at the instrument voltage regulator on the back of the cluster, Could be a bad connection at the dash harness plug, a failed PC board, or a bad IVR.

 

[vintageman]

Thanks Hemi, I will try a different meter and if nothing, try a test light. More to follow.

Tom

 

[Don C]

Because the rest of your gauges function the instrument voltage regulator is not at fault and is functioning. I would start checking the yellow/white wire as close to the instrument panel that you can. If you don't have any voltage on that wire there, you will likely have to pull the gauge cluster, the problem will then likely be at the printed circuit board connector, or in the circuit board. Make sure you're getting a good ground with the negative lead on your test meter or test light. You can use a needle to penetrate the insulation on the wire and then connect the meter to the needle. Even though it is inside I still put a dot of liquid tape on the hole to keep the insulation intact and the copper sealed from the elements.

 

[vintageman]

Thanks for your advice Don, hopefully I can figure this out without removing anything else but will if I have to. My cluster is hardwired and does not use the printed circuit board so barring a bad connection there, hopefully a different multimeter will show the fluctuating voltages. I will be checking these things again tonight when I get out to the car.

Tom

 

[vintageman]

Guess I will be pulling the cluster to test everything. I used four different brands of multimeters tonight and a test light and did not get any power coming from the kick panel plug or at the sending unit. Is there a way to bench test both the tac and the fuel gauge once I pull the cluster out? I guess I will use this time for installing LEDs in my cluster as well. Thanks everyone for your help and advice.

Tom

 

[midlife]

There's a handy gauge tester now available:
https://desertclassicparts.com/product-category/gauge-testers/

 

[vintageman]

Thanks everyone for your input and advice, I got the fuel gauge working tonight. I went by a mustang friends house this afternoon and while going through his storage units, I noticed he had an instrument cluster for a 71-73 mustang. It had the speedometer and the fuel gauge in it, so I asked if I could have it. He gave it to me and I checked with my ohmmeter when I got home and it read about 14 ohms so I installed it and put some gas in the tank (It had run down to empty while tuning it), 5 gallons Gave me just under 1/4 tank and another 5 gave me just over 1/2 tank. Close enough for right now, Once I get it fully timed in after replacing the intake and carb over the next week, I will pull the new sender and bend the arm to get a little closer to accurate readings.

Btw,, I picked up an edelbrock 2 to 4v Performer intake (I think 2150) and a Summit 750 carb. The current Holley 500 com carb ia not cutting it. Hopefully a "first drive" video will be coming soon. More to follow.

Tom

 

[vintageman]

So now that my fuel gauge is working correctly, does anyone have any advice for the inop tac? When I had the cluster out, I verified that the black cable going to the tac has continuity from one pin to another and the mating connector has 12 volts when the key is turned on. I have tried the slapping the dash technique and it did not work (tried multiple times). Any further checks? If necessary, is there a plug and play aftermarket tac gauge available that looks OEM or close and fits the cluster correctly? Can the original be repaired? Thanks.

Tom

 

[midlife]

The original can be repaired, but finding people willing to do so are few and far between. If you have continuity between the two pins, that means that the input transformer is still good, but the guts of the gauge are bad. This failure allows you to continue running the engine with an inop tach; the reverse damage won't allow the car to run unless you bypass the tach.

Rocketman (RCCI) is a sponsor here who can replace your tach with an aftermarket look-alike but that does require some minor re-wiring.

 

[rackerm]

So now that my fuel gauge is working correctly, does anyone have any advice for the inop tac? When I had the cluster out, I verified that the black cable going to the tac has continuity from one pin to another and the mating connector has 12 volts when the key is turned on. I have tried the slapping the dash technique and it did not work (tried multiple times). Any further checks? If necessary, is there a plug and play aftermarket tac gauge available that looks OEM or close and fits the cluster correctly? Can the original be repaired? Thanks.

Tom

I am not familiar with your Duralast distributor, but the Ford factory tach uses current and not voltage to operate. Is the tach still connected to the factory tach wires from the coil to the tach? Typically installing aftermarket distributors and coils requires bypassing resistor wire in the factory wire harness to provide the distributor and coil with 12v. GM and most aftermarket tachs use voltage. Rocketman can help you convert your tach to use voltage or repair it.

Here is an excerpt from a magazine article on this topic.

A Ford tach's peculiar problem: The preceding are common generic issues across all manufacturers. However, there's an added wrinkle with legacy Fords. On most factory and aftermarket tachometers, the signal wire connects to the negative (-) side of the ignition coil. But most Fords with points-triggered ignition systems have a two-wire inductive tach that connects to the coil's positive (+) terminal, piggybacking onto the ignition "run" circuit from the ignition switch to coil (+). Remember, on a points system that circuit incorporates a ballast resistance wire. Upgrading to a modern ignition requiring full-time 12 volts requires getting rid of the resistance wire. Without resistance in the circuit, that old Ford tach won't work!

Built for failure: This Ford design is still problematic even if the ignition system is still stock, particularly as originally designed back in the 1960s: The OE Ford tach wire is inline (in-series) with the ignition "run" circuit. In other words, the ignition switch's "run" wire passes through the tach and then on to coil (+). If the original tach ever shorts out, the car won't start. Total electrical failure. By 1973, Ford marginally improved this circuit, with the tach now wired in parallel (not directly in-line, there's an added "bypass" wire around the tach). At least in theory the car should at still run if the tach shorts out. Wanna bet your engine on it?
Incidentally, if you ever connect the stock Ford two-wire tach to coil (-) by mistake, that error will fry the tach for sure. Any way you slice it, updating the Ford design is a critical reliability and safety fix.

https://www.motortrend.com/how-to/update-ford-tach-and-turn-ammeter-into-voltmeter/

 

[vintageman]

Thanks for the replies. The distributor is a “plain jane” duralast brand from autozone. Still uses the point style ignition and rotor and regular small cap. I have the wire from the gauge harness plugged into the coil, not sure if positive or negative right this moment (i’m at work but will check tonight). Which side is correct for the stock tac?
Also, when I bought my gauge harness, I got the one for center gauges since I have those. Is there a difference in the gauge harnesses that would make a difference, maybe they sent the wrong one? Thanks.

Tom