Author Topic: Tach in not working  (Read 2270 times)

dab67

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Tach in not working
« on: February 23, 2007, 02:57:58 PM »
Help!!!!!!!!

I just replaced the underdash harness in my 67 Camaro and now I can not get the in dash tachometer to work.

What side of the coil does the yellow and black wires that are together and the single black wire go on. Does the two go to the positive side or to the negative side? Does anyone have diagram for the coil wiring? Also which vacumn port on the carb goes to the Distributor Advance?

dab67


rich69rs

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Re: Tach in not working
« Reply #1 on: February 23, 2007, 06:20:18 PM »
The two primary circuit wires from the ignition switch connect to the + terminal of the coil.  Both the wire to the distributor and your tach lead connect to the negative terminal.

When the ignition switch is in the start position, the ballast resistance (or resistance wire) is not in the circuit, and a full 12 volts is applied to the primary winding of the coil for starting.  After the engine starts and the ignition switch is in the "on" position, the ballast resistance wire is now in the circuit and the other wire is not.  The ballast resistance drops the voltage from 12 to somewhere around 7-9 volts, enough for running while saving wear and tear on the points in the distributor. 

Attached pic is typical.  It shows a ballast resistor in the "start" circuit.  Sometimes GM used a ballast resistor and in other applications GM used a special resistance wire of a given length to create the required resistance to drop the voltage from 12 to 9 or so.  Not sure of other years, but my '69 has the resistance wire which is easily identified by the cloth like material that covers the OD of the wire.

Port on the carb for the vacuum advance is generally just above the throttle plate.   That being said, check out the previous discussion and especially JohnZ's comments.  http://www.camaros.org/forum/index.php?topic=64.0
« Last Edit: February 23, 2007, 06:29:43 PM by rich69rs »
Richard Thomas
1969 RS

dab67

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Re: Tach in not working
« Reply #2 on: February 23, 2007, 06:32:52 PM »
Once again whether it is you Rich or John, one of you two always comes through.!!!!!!!!

I think I need to start paying you two!!!!!!!!!!!!!!!!!!

dab67

dab67

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Re: Tach in not working
« Reply #3 on: February 23, 2007, 11:00:54 PM »
OK let me add a little more mystery to my problem. And see if I explain this correctly. My clusters mounted in the dash has the Speedometer on the left and the Tach  (5500)on the right (not trying to be funny just trying to explain) I have a center console (Auto) with gauges, fuel, oil pressure, temp etc.
I purchased a new V8 underdash harness for auto console and factory gauges, hooked everything up and the tach and right turn signal in the dash do not work. Now I only have one terminal connection to the back of the dash cluster that I am figuring powers the whole cluster. So what am I missing??? Did I blow something out in the connection between the two clusters or what? Or am I completly losing it? Is there a seperate harness just for the In dash Tach? I see there is one for the 69 but it is for cars without the console gauges. All the wires to the coil are hooked up correctly so I have no clue what is wrong.

dab67