Can anyone say what the form of the TD (engine speed) signal is?
Square wave? Sine wave? Pull-down to ground?
Has the TD signal been the same over a long period of time, or has it changed over the years?

Since no one has been able to give you a specific answer in nearly a week I'll offer the following.

When I was a grad student at the U. of Wisconsin Engine Research center back in the late sixties I had a 283 Chevy V-8 on a dyno that I was using for emission related research.

The setup had a magnetic pickup that detected a TDC signal as the timing notch on the crankshaft torsional damper passed by the pickup. It was a short, sharp voltage spike that was displayed on an oscilloscope along with differential pressure data across the air and fuel flow paths from low response time pressure differential transducers.

So, if you have a scope with an inductive pickup that you can connect across the TDC signal wire to the EZL you might be able to characterize the wave form of the M103 TDC signal.

Duke

The voltage generated by a reluctor, aka "magnetic pick-up" is a sine function. That sine signal is the input signal that is used by the switchgear or EZL to control the ignition.
The switchgear or EZL also creates the TD signal which is used as an input signal by the tachometer, fuel pump relay, AC compressor controller, idle speed controller, etc.
The original question is: What is the form of that TD signal which is created by the switchgear or EZL?

I scoped out the TD signal on a 87 300d. Sign wave 4 to 6 mV into the ECU and a 5 v square wave out for tach, ac etc. Never looked at an EZL.

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92 e300d2.5t
01 e320
05 cdi
85 chev c10

db:

Much appreciated. That the TD signal is a square wave is not a surprise; it could have been 5V or 12V. What is a surprise is how low the input signal is; was that at idle speed?