How to automate continuity tests on harnesses with up to 200 connections

Question

I have some dozens of wiring harness, and always buying more. Nowadays I need to test connection by connection through continuity test with a multimeter and checking on the documentation in order to verify if each harness were build correctly. I definitely need to find a way to make it automatically. That's why am here... Please bring me ideas how I should design a circuit to accomplish that.

A few considerations:

1. Each harness can have between 40-200 connections.
2. Each harness has one automotive connector at one end, and a few hypertac connectors at the other end.
3. At one end, each harness has only one automotive connector w to 200 pins each (rarely fully used)
4. At the other end, each harness has a few hypertac connectors w 90 pins each (sometimes fully used)
5. I do not have many resources, that means the solution should as cheap as possible.

Doing this manually, I check on the mapping doc then I test continuity b/w the two pins, but to do it automatically the hardware must have to test each pin at one end w all pins at the other end. I think it should be like a switchable loopback between several pins.

Comes in my mind to using 90+200 = 290 relays and control them w I2C, but it does not look a good nor elegant idea to have this rude amount of relays operating.

Answer 1

You don't need relays (unless you want to test the cables at full voltage) - you can hook the logic signals up to the cables directly. I would go with a bunch of I/O expanders (or shift registers, which can be used as I/O expanders) and a program like this:

1. Set all I/O ports to input with weak pull-up (or build the pull-ups into the circuit)
2. Set one I/O port to output low
3. Read all of the I/O ports and verify the connected ones are all low and the unconnected ones are all high.
4. Repeat steps 1-3 with each different pin as the output.

I suggest making a tester with 290 ports, so it has enough ports for all your types of cables. Then, make an adapter which plugs into the tester and the cable. That way, you can test different types of cable with the same tester with different adapters.

Don't forget ESD protection.

Answer 2

So you definitely need to connect all wires to connectors, some manual labor is required. But other than that it's a relatively simple board design project.

You would probably need something like a matrix of switches to address each wire, then apply voltage on one end and scan the other end. You would get a table matching both ends. Everything should be controlled by a microcontroller, or maybe by a PC, whatever is easy for you to code.

I think, that you should not do it by yourself. Find a contractor that is capable, they can do it quicker and cheaper then you will.