The EGT and CHT wires together will be fine but I would not run them next to (or even near to) spark plug wires. I had a problem with jumpy EGT readings at first and fixed it by getting farther away from a plug wire.
 
With good-quality filtered differential signal conditioning for the thermocouples it probably won't be a problem, but best practice is to minimize routing them parallel to the plug wires.
 
You can bundle engine sense wires together. Probably not a good idea to route these wires with higher power items, like main bus feed, master or start wires, or any large wires that carry a lot of current. I have only two firewall penetrations in my firewall that carry wires.
 
N96TJ said:
I had a problem with jumpy EGT readings at first and fixed it by getting farther away from a plug wire.
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Thank you Tom. I was puzzled recently by a synchronous deviation of CHT and EGT proximity to a harness explains it.
 
I have a Dynon engine monitoring system and there was a slight fluctuation of EGT when the wires were run next to the spark plug wires.
 
but don't route them with the com antenna leads like I did. they spike with every broadcast.
 
The instructions that came with my EDM-350 stated to route them separately from the spark plug wires.

So I did.
 
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