Jim, the module in question is the EA/CC/ISC (pin 7, E-GAS module) on an M119.974, 1994 vintage. I've been using the impulse count method but as you can see in that attached photo, there are 14 different possibilities for impulse code 2, and I want to narrow that down to one of the 6 codes the HHT would display.

I'm purchasing a used Trisco Palm Scanner, which should arrive in 3-4 days. But someone else who owns one told me it won't show the 3-digit codes like the HHT, only the impulse count code (i.e., only showing code "2", same as my LED blinker box). But I really don't know which is correct.

I'd love to buy a real HHT but I have no idea where to find one used, or how much they cost (new OR used). I've never even seen one!