Shielded cables and saving pins on an AS connector

Given the following sensors:

* 2-pin knock sensor

* 3-pin cam angle sensor (hall effect)

* 3-pin crank angle sensor (hall effect)

Just how many pins do you REALLY need at the firewall bulkhead connector?

1) All three use a signal ground, which is merged at the ECU. Would it work to merge them in the engine harness instead, saving 2 pins?

2) All three use shielded cables. Would it be okay to combine them all into a single (shielded) cable, reducing harness girth?

3) Do all three shields need separate pins, or can they be combined then broken back out on the other side of the bulkhead connector?

4) Does the common +8V source between the cam/crank angle sensors need to be shielded at all?

Worst case scenario: 11 pins

* Knock shield

* Knock signal +

* Knock signal -

* Cam shield

* Cam +8V

* Cam signal +

* Cam signal -

* Crank shield

* Crank +8V

* Crank signal +

* Crank signal -

Best case scenario: 6 pins

* Common shield

* Common +8V

* Common signal -

* Knock signal +

* Cam signal +

* Crank signal +

A savings of 5 pins is significant - it means a whole shell size for an AS connector, not to mention potentially the ability to use a single 4-wire shielded cable instead of 1x 2-wire and 2x 3-wire. But is this realistic? Will the signals interfere with each other inside the shielded cable, or will the drain function to collect that interference as well as outside interference? (eg, is crosstalk something to worry about?)

How far between the ECU and the firewall connector/ If it just a couple of feet, you can have a single shared ground for the shielding. But if you intend to continue running shielded wiring from the bulkhead to the ECU, then I would have 1 pin for each shielded cable.

I would not tightly combine multiple high-speed signals within the same shielding. If you are going to the trouble to use shielded wire, then respect the shielding.

Do you have something against big shell sizes? It takes what it takes -- don't compromise all the extra effort your doing just to save pins.

Great question, I was wondering the same thing. It sounds like using a 4-wire cable with 4 signal wires within that cable isn't a good idea. How about 4 individual shielded cables sharing a common ground lead through the AS connector?

I typically share a common +8V. Is it ok to share a common signal (-) as well?