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Discussion Starter #1
Here is my situation:

I just completed the removal and replacement of the dash in my 74 gtv.
Purchased new dash from Centerline. Looks and fits perfectly.
Okay now for the problem:

I reinstalled the clster hooked all wires up I believe. Car starts and everything works except for the coolant temp gauge, and the speedo is acting erratic. Needle shakes until it hits 40 mph. then it calms down. But i do not believe it is accurate. Before I take it apart is there something I should be looking for? Any help would be appreciated.
 

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Here is my situation:

I just completed the removal and replacement of the dash in my 74 gtv.
Purchased new dash from Centerline. Looks and fits perfectly.
Okay now for the problem:

I reinstalled the clster hooked all wires up I believe. Car starts and everything works except for the coolant temp gauge, and the speedo is acting erratic. Needle shakes until it hits 40 mph. then it calms down. But i do not believe it is accurate. Before I take it apart is there something I should be looking for? Any help would be appreciated.
I assume it's the same temperature sender and same gauge that you had before the dash replacement, right? Not sure how this works in a '74, but I know that I had some issues when putting my dash back in with ground to the gauges...I would check that.

As for the speedo, I would probably grease the speedo cable first, and see if that helps
 

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To check if the gauge itself is working, turn on the ignition and ground the temp gauge sending unit wire to the engine or body. If the gauge goes to full hot, it's working. If it does nothing, you need to search for the problem.

So the gas gauge and oil pressure gauges work? They're all on one electrical circuit together. On my 72 Berlina, it's fuse 6 I believe, but you should check a wiring diagram. If the other two electrical gauges work and the just the temp gauge doesn't, it's specific to that gauge, and could be ground, power wire, or the gauge itself.

Andrew
 

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Discussion Starter #5
Process of elimination

Andrew

thanks for info.

I did as you recommended pulled power wire from sending unit and grounded to engine.

Gauge did not register when ignition key turned on.

All other gauges worked fine.

Fuses seem okay.

So I should be checking for proper ground wire, Would that ground be attached to where the dash is bolted to. There are a few wires there that I noticed. Then I check the power wire. How do i check that? If all else is okay, then the gauge may be faulty?

Thanks again
 

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Generally, older Alfa gauges have a "jumpered" ground that runs from one gauge to the next, then attaches to ground on the chassis at one point. Your specific car may be different. Are you sure you're getting power to the gauge? Also, certainly gauges do go bad too, so that's possible.

Andrew
 

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Discussion Starter #7
Stumped

Andrew

not sure if I am getting power to the gauge.

Dumb question, how do I check if that is the case?

I checked all the grounds all other gauges are working fine.

I do have an interesting item, I replaced the hazard button when I replaced the dash. The first way I wired it I blew the 3 fuse. I replaced the fuse and the way it is wired know only the right passenger rear and front lights flash on and off. This is probably not related to the temp gauge correct?

I will save that question for another posting.

Thanks
 

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Isn't there a jumpered/common hot wire to the gauges? With the key on, I would see that you're getting power to the other gauges, then trace why you're not getting power to this one. I'd use a small probe-type test light to touch the hot terminal.

I'm not working from a wiring diagram, but from memory. But there must be a (1) gauge power wire, (2) sending unit wire, (3) gauge light wire, and (4) ground wire to each gauge, shouldn't there? Someone with a diagram handy can correct me if that's wrong.

Andrew
 

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There are three wires going to the gauge: hot, ground and signal. Hot is pink; ground is black and signal is possibly brown. Connect a volt meter between black and pink. You should see about 12 volts. Disconnect the brown? wire from the meter and measure the resistance between it and ground. It should be about 1000 ohms, depends on the temperature. If it is 10K ohms or higher then you have either an open circuit sender or a broken wire to the sender. If you don't have 12 volts between black and pink then you have a wire off on the guages that should be easy to identify.

If it looks like your sender is bad, disconnect the wire at the sender and measure the resistance between the sensor terminal and ground. It should be around 100 ohms.

If you jump between pink and brown?, the gauge should read maximum temperature. If you have a 10K pot, connect it between pink and brown. You should be able to make the gauge read between cold and hot by varying the resistance. The sender is resistor that changes with temperature. Higher temperature = lower resistance.

Reply if you need help interpreting your data.
Ed Prytherch
 

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Discussion Starter #10
Update;

Ed, Andrew

sorry for the delay in responding. I left for Europe on July 18th and got back mid august.

So, I finally was able to get into this problem. Ed I followed everything you said in your post all checked out.

So after beating my brains:confused: I came up with the idea maybe the needle is stuck inside the cluster. I removed the cluster and removed the back instrument panel, and believe it or not that was the problem.

Somehow when I originally removed my dash and instrument cluster, I disasembled all for a cleaning and bulb replacement. I guess when I reassembled the cluster the instrument needle on the temp. gauge got pinched.

So in closing I wish to thank both you guys for your assistance. I learned a bit about wiring.:)

Thanks

Tony
 

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I am going through this right now and am going to get my trusty Ohm meter out to check continuity. The sender seems to work, so its either the wiring to the gauge, or the gauge itself. Who knows where to get a gauge repaired, or a refurb or new one?
Thanks,
Jim
 

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There are three wires going to the gauge: hot, ground and signal. Hot is pink; ground is black and signal is possibly brown. Connect a volt meter between black and pink. You should see about 12 volts. Disconnect the brown? wire from the meter and measure the resistance between it and ground. It should be about 1000 ohms, depends on the temperature. If it is 10K ohms or higher then you have either an open circuit sender or a broken wire to the sender. If you don't have 12 volts between black and pink then you have a wire off on the guages that should be easy to identify.

If it looks like your sender is bad, disconnect the wire at the sender and measure the resistance between the sensor terminal and ground. It should be around 100 ohms.

If you jump between pink and brown?, the gauge should read maximum temperature. If you have a 10K pot, connect it between pink and brown. You should be able to make the gauge read between cold and hot by varying the resistance. The sender is resistor that changes with temperature. Higher temperature = lower resistance.

Reply if you need help interpreting your data.
Ed Prytherch
I’m having an issue with my temp gauge reading low. It goes to max when brown wire s grounded.

my findings have been, all cold engine,

at gauge red-ground 11.98v
Brown-ground 2850 ohms, alternative new wire from sender to gauge same reading,
Brand new Sender-ground (on engine) 2840 ohms
Old sender with the thread on engine, grounded to engine 2300 ohms
Old sender tip-paddle terminal 2700 ohms

so by your above explanation it would seem my old and new senders have too much resistance, the wire is good. That would make sense with the low reading gauge. But I then have the old and the new senders both faulty?

I got the new sender from classic Alfa, new, is there an alternative sender for a 1750 gtv, or could it be another issue? Ie. engine ground

thanks
 
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