How many, and which, pins does the code scanner actually use? For OBD1, would it just use the data stream pin or pins? I've made up some jumpers so I can "reconfigure" the connections between the ALDL and the scan tool.
From the ECM, does the actual data stream/streams have voltage on it? It's seems it would have to have voltage but I'm not sure.
The Bosch manual doesn't actually get down to this level. I'm wondering if maybe it is just looking for the data stream on a different pin than what the truck is actually using, because it sounds like there could be a few variations.
Last question (for now)...where exactly is the CEL located on the instrument panel? The only 2 indicators that are doing anything are in the bottom right. All the gauges work, and the back lighting works as well.