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1970mcss

Need help with a Tachometer problem

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I need with my tach, I drove my Monte to work this morning. First time this year and after I had the dash cluster out to replace bulbs and clock. On the way to work the tach worked fine. When I started the car to come home the tach wasn't moving. I checked the wires at the coil and they are all connected. Is there a fuse or something to check in side the car?? Or any hints on what to look for???

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I'm going to step out on a limb here, going from old memory. I'm going to assume you drove the car home fine just with no Tach. My guess is its mechanical (gauge) because I don't think the car would run/be drivable if you had a bad wire/electrical issue. I'm sure someone will correct me and or give more info on troubleshooting. 

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It did start and run fine but I think the tach runs off the coil. All the wires on the coil were in tact. I can't remember if the tach runs off the printed circuit or directly wired. I'm hoping that someone has some info...

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The wire coming from the coil goes into the 12 pin cluster plug. The tach has two nuts and two washers that go on the studs on the tach. The PCB slides over the studs and then a washer and nut on each stud to drive the tach. Could be the PCB at the stud has a tear in the copper line or the nut has come lose.

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I will check the back of the tach, I'm guessing I can get at if from the top with the dash pad taken off??? 

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Make sure you disconnect the battery. You might find it easier to reach coming from the steering column area. Coming from the top you have the wire harness to deal with and the PCB can get damaged.

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Good point, and I would much rather not have to remove the dash pad again, I will report back.

Thanks

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Ok while Paul is trouble shooting educate me. Back in my blue oval days if there was a wire/voltage/connection issue with the Tach the car would turn over/crank with the key in the Start position but would die when the key was returned to the On position, are the bow tie's different? 

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2 hours ago, DragCat said:

Ok while Paul is trouble shooting educate me. Back in my blue oval days if there was a wire/voltage/connection issue with the Tach the car would turn over/crank with the key in the Start position but would die when the key was returned to the On position, are the bow tie's different? 

I have never heard anything like that.  To me, a Tach is nothing more than a meter that measures RPM's just like any gauge taking a reading.  Not sure why Ferds would be any different.

rob

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Thanks for the info, I didn't want to steal the thread but needed an education. Don't ask me why the blue oval people did some of the things they did, I just remembered this from my younger days lol You had to jumper the +side of the battery to the +side of the coil to troubleshoot and bypass the ignition circuitry when testing. 

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Paul, I may have missed this but is this a factory OEM tach / gauge package or aftermarket?

My 71 has the gauge package I took from another 71 350 (NON SS) car. Perhaps 70 to 71 they changed the wire layout but my tach runs off a single brn wire that has it's own hole in the firewall. (picture)

I am going by memory so I could be wrong, sorry... I'm looking for more pictures but no luck yet.

Bruce

 

IMG_0359.JPG

IMG_0309.JPG

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Thanks Bruce, the car has factory gauges.  I will take a look. I had the cluster out over the winter and was very careful to put it all back together. I will look for the single wire. I will keep you posted

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I checked all wires and everything was tight and right. I wiggled the ground wire and off course the tach is now working. But still to questions. Where can a guy or gal get the flex hose from the heater box to the lap cooler? And now i notice a ticking noise in the radio, do i need somekind of noise surrpressor. Not sure if my decription is good but let me know.

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Ticking noise in radio, does it change with the engine speed?

Solid copper spark plug wires I believe can cause this. There is some small round thing attached to the ign coil that looks like a condenser but it's a ? noise suppressor.

 

 

Back to the tach, the ground is critical to the dash. I posted a picture or two of my 71 NO A/C Monte if it helps.

I think these are two different grounds, sorry I don't remember for sure but I don't think the IP ground (left pic) attaches to the screw on the parking brake (right pic). I think the IP ground attaches to the steel frame of the dash assembly and another wire from the steel frame to the parking brake screw, I think! It's been a while.....

Bruce

 

IMG_0314.JPG

IMG_0321.JPG

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I will check the plug wires although they are new. I looked at the brown wire at the fire wall and noticed that the grommet was pushed in, I'm going to take a close look at the wire and make sure it didn't rub threw. I have to try to push the grommet back into the hole so it stays put. I will look into a radio suppressor. Thanks

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