back probe/ newb question

I'm testing sensors and reading manual but what does it mean to back probe?

am I supposed to pierce insulation?

Unfold a paper clip and slide it into the back of the connector where the wire goes in until it makes contact with metal. Then clip on your leads from you meter and you will be able to measure the values at each wire.

Correct. You can use a straightened paper clip, small straight pin, or a dedicated "backprobe pin" like Fluke makes to slip in to the backside of the connector.

If your DMM uses "shrouded banana plugs" to connect the test leads, you might want to look into the Fluke "sure grip" leads - which have the shrouded banana plugs on both ends (one straight, on 90*) and you can get a number of probe tips for different applications. Also, you can get (for $30 or so) a set of test leads with "five-way telecom test clips" on the ends, which are EXCELLENT for general automotive use (they have a bed of nails and a pressure pad in the clip, which works well for getting into connected wiring quickly.)

Information on all these goodies can be found at www.fluke.com (I think that's correct - I usually use Google to find things...)

5-90

It means with the connector connected and to go in the back of the connector to get a reading. You can use the paper clip methode, but I've had iffy results with this. I usually remove the silicon/rubber gasket (grommet) around the wire in the rear of the connector, slide it down the wire some. They aren't to hard to get out most times, all it takes is a very small screwdriver or a really pointy punch (awl). Then stick my ohm meter probe in the back of the connector, I usually get a better contact this way. I've had trouble getting a good contact using a paper clip or piece of solid core wire on occasion.