Discussion and questions related to the course Practical Harness Construction - Club Level
I'm in the middle of planning a harness design.
Planned ECU is Link G4+ Thunder.
Engine is 13B turbo installed in series 3 RX-7.
I am putting two thermocouples in the exhaust/turbo manifold to measure EGT for each rotor.
The Link Thunder has provision for direct input for two thermocouple sensors, removing the need for an amplified/analog signal converter.
So far so good.
I have two questions however:
Firstly, the thermocouple inputs are in the 'D' loom connector which is a 26 pin AMP Superseal connector. I have found contacts suitable for thermocouples for Deutsch and Autosport connectors, but not AMP Superseal.
Is anyone aware of a source for contacts suitable for this purpose?
Presumably they exist, otherwise the direct thermocouple inputs would be useless. Yet I haven't found any further info in the wiring manual in PC Link or on the Link forum.
The second question is relates to harness design for the thermocouples.
The wiring harness will enter the engine bay on the left (passenger for RHD) side while the themocouples will be on the right (driver's side for RHD). If I was using a thermocouple amplifier, I would most likely separately route the thermocouples to enter via the RHD/driver's side of the engine, then mount the amplifier somewhere near the ECU and plug the thermocouple leads into that. This is neater and improve serviceability, so I could easily replace the thermocouples if they failed (foreseeable possibility on a turbo rotary).
The direct input would mean it makes more sense to bundle the thermocouple wires with the rest of the wiring harness. Would it therefore make sense to terminate those wires on the engine side with female thermocouple connectors (the two-prong style plugs where you screw in the wires) and then have a sub-harness for the thermocouples with male connectors on the sensor side? Having a subharness for the thermocouples would allow easy replacement without taking apart the whole loom and perhaps make it easier to route the harness (without having angled thermocouples hanging off the end). I image the connection point would need to be located a distance away from the exhaust itself, with perhaps the thermocouples have a good 80-100cm of wire to the male sub-harness connectors.
Am I on the right track with the design on this point or are there any tips to improve it?
Any help much appreciated!
You can just use normal superseal pins for the TC cable connection to the ECU since it is the measuring device and has cold junction compensation built in. All other connections in the TC circuit external to the ECU need to be of the correct metal.
Im not quite sure I understand your question about the routing, but will give some comments that may be relevant: It is fine to bundle the TC wires in the main harness, many choose to use shielded TC wire for this since they are such low voltage signals but I have also seen many successful installs using un-shielded TC cable bundled in the main loom too so I dont have enough personal experience to confidently say you need it or not.
Typically rather than a subloom you would just have one connection point per TC somewhere that the TC's lead/pigtail can reach. That connection point can either use the mini TC connectors (cheap) or DTM or AS with the correct pins ($$$). Another common option you see in drag cars is the mini "panel mount" TC connectors somewhere in the firewall - have a look at Omega RMJ or MPJ for examples of this option.
That's extremely helpful. The fact it can use conventional pins on the ECU makes things much simpler.
I think you understood me well about the routing. Since the TCs connect directly to the ECU, it makes sense to have them routed with the main engine harness. The downside this introduces, however, is that if you ever needed to replace the TC, you'd need to take apart the whole loom, hence having a connection point for the TC leads to reach. Here I'd likely use two 2-pin DTM connectors with the appropriate K-type contacts.
I have attached a basic diagram to illustrate what I mean. I think it matches the typical setup you described.
Those Omega firewall panel connectors would be perfect for a conventional setup with amplifier module somewhere in the cabin and might work well for my purposes too, although it would require a connector on the ECU side of the engine harness for TC wire to run to the cabin side of the connector panel.
FWIW, the experience I've had with the Deutsch TC contacts has been less than positive. They fail after a couple of cycles, it seems the material is just too soft to last. I would recommend sticking with the typical mini TC blade connectors, it will save you time/money/frustration down the road.