IRstuff,
My apologies for missing your post. I thought this had run it's course with responses.
The number of devices doesn't matter. Here's an example of what is wanted. The Ford FRPP Copperhead Control Pack PCM doesn't have a VSS (Vehicle Speed Sensor) out. Let's say the shop in question is doing a resto mod on a F150 and installing a 5.0 Coyote engine and a Tremec TKO transmission (manual). Ford, for the F150 used an electronic VSS and the output to the instrument cluster came from the PCM. The Tremec allows for both a cable\gear speed output or an electronic VSS sensor. If the proper 8,000 pulse VSS for the Tremec is used the sensor output can be directly spliced in to the original PCM VSS input and will output the information to cluster. The cluster will accept the signal with no problems. The original PCM won't discriminate against the new sensor. It won't notice any difference.
---Bear in mind the FRPP Copperhead PCM does nothing but control the engine with limited extended functions like for the effects of running AC. There is no interference between the trucks original PCM and the Copperhead. The only way any interference "may" be involved is if they try to communicate with each other. Both the OEM PCM and the Copperhead PCM use the J1850 protocol for the CAN. The difference is the Copperhead uses the newer, extended format Bus, ISO 15765-4 which didn't become the mandated US standard until 2008 although most vehicles were compliant in 2006.
(I've tried to upload an image here but I'm not sure what's going on with images or pasting to the forum. The image button does nothing. Nothing seems to work although as an attachment it might have?)
Not looking to write an essay (I've been informed not to in the past) but it is the ISO 15765-4 that I'm concerned or unsure of. I don't think there will be any issues collecting the data needed to get it to the cluster but my primary concern is protecting the Copperhead PCM. I'm thinking if I use a diode I can protect any unwanted signals trying to communicate with the Copperhead. Problem is I have no idea of what diode(s) I would need to use to test the transfer of information to the OEM PCM. I'm not even sure a diode would work for this application. Ultimately I don't think I'll have any problems with the engine signals like the oil pressure or coolant temperature from the Copperhead but I'd feel better with some insurance.
I hope I've made myself clear with this???? If not please let me know. Signal interference from multiple standards was mentioned but there really aren't multiple standards for the information I'm wanting to collect and transfer. ISO 15765-4 does allow for extended signal formats but it doesn't mandate all signals to be extended. From what I'm told it is primarily used for capabilities like traction control where information from multiple sensors are used at once.
If this is too long please let me know. EDIT: Ah, the attachment is the datalink by protocol.