Autonerdz forums

Hello, fellow nerdz. I do a lot of harness repair and something just hit me - I see improper back probing every time, and I see it is all publications /videos/conferences that are held by pro auto techs. Most people back probe in a way that damages the weather seal of connectors. If you have never taken apart a connector, you will do something that seems logical but will end up damaging weather seals.

The improper way (but what SEEMS logical) is to back probe into the same hole the wire enters the weather seal. If you do this, you will get a connection, but you will puncture the weather seal and it will slowly tear itself all round as it heats and cools in the engine bay.

Sometimes when you insert your back probe, you feel the pin stick and get caught. Most techs force the pin inside when they feel this, and what you will feel is the pin will resist then proceed on as normal. NEVER do this. The reason it gets caught is that the pinhead has entered the crimp area. If you force it in, the pin will open the crimp area and proceed to go in. The unfortunate thing is this will feel very tight and you will get a connection but you have damaged your crimp.

If you want a good connection, you can do one of two things. Either remove the probe and just go opposite that point of entry (recommended) or push the probe forward (not recommended). If you choose to push the probe forward, you will get a connection at the pinhead itself like so....

Finally, some car manufacturers use a very funny type of weather seal that becomes hard like contact cement (I'm looking at you Citroen, Peugeot, you bloody weasels). If you try and rape the connector you will destroy a lot of probes, and if you have a probe strong enough and loaded with viagra, what you will find is after it wins the entry, it will come out with the entire pinhead. In a case like this, save yourself the hassle and just pierce the wire.

fisher wrote on Jul 21^st, 2019 at 10:34pm:


Fisher, do you think that a bit of lubrication helps you get it in?

Agreed nice work!   

Logic wrote on Jul 22^nd, 2019 at 5:05am:


Please point me to the post or page of what you make.

By the way sometimes I do not make break out leads, rather I make extension leads with a marked zone in the middle where I will use insulating piercing probes.

I do that so as to not waste construction components on a lead that I may not use that often.

In the event that I use it frequently I can complete it with 4mm banana jacks to a complete lead.


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Logic wrote on Jul 22^nd, 2019 at 2:45am:

I wish I had a picture of the PCM breakout box for Maserati. It is probably 2' wide. Maserati definitely took Picoscope diagnostics seriously.

Logic wrote on Jul 24^th, 2019 at 6:44pm:


That's the one! I'd love to have something like that for Land Rover (Bosch PCM).

Steven McGrew wrote on Jul 27^th, 2019 at 12:30pm:


I could use one to respond to your post!   

Logic wrote on Jul 27^th, 2019 at 2:41pm:


I have seen pictures of Ian's breakout leads. They are second to none!

K-Mech wrote on Jul 21^st, 2019 at 9:59pm:

Thank you K-Mech! I am one of the ones who was doing this incorrectly, but not anymore!