Quote:
Originally Posted by joeydurango
So I guess that means no one knows what the brown wire should read at idle? I'll just see what I get, if anything. ZAP!
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The brown wire connects to the negative side of the coil. When the points are closed (or the transistor in the HEI module is conducting), that side of the coil is connected to ground. When the points are open (or the transistor in the HEI module is not conducting), that side of the coil is no longer grounded so there will be voltage present. So with the engine running, there will be voltage pulses present on the brown wire. The tachometer responds to the frequency of these pulses (which is directly proportional to the engine speed).
You can connect a 12V test light to the brown wire and it should glow at nearly full intensity with the engine idling. And should get dimmer as the engine speed is increased. With a voltmeter connected to the brown wire (and set to DC Volts), I believe you should see a reading of 10V or higher if the connections are okay.
Quote:
Originally Posted by HO455
All the symptoms of a bad solder join inside or a bad connection/broken trace on the printed circuit component on the back of the guage panel.
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Quote:
Originally Posted by custom10nut
The tach operates separate from the printed circuit. I had similar issues with my original tach, and after tracing wires, I found that the printed circuit doesn't contact the electrics of the tach
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True, the tach does operate separate from the printed circuit on the back of the gauge panel. However, there is a small printed circuit board (with soldered-on components) that is part of the tachometer assembly (located right behind the tach face). And if all the external connections check out okay, the symptoms sure do sound like there is a bad solder joint on the tach board.