Importance of Voltage Drop Test!

My Mountaineer master and passenger door locks didn't work in the lock position, only in the unlock. After a couple of checks it led me to a four wire splice which was under the left rear door jamb. A couple of thing had to removed to get to the harness.

I take voltage reading after the splice on the wire that goes to the left door switch. I have system voltage so you assume the problem is further up the harness right?

But look what happens when I loaded the circuit by pressing the lock button...I did the same on the wire going to passenger lock switch with same results.

To verify I used another wire probe as a jumper before the splice and after. Now the door locks. Splice has to be the culprit.

I sliced opened the heat shrink.

Imagine if I wasn't aware of the loaded circuit test. Door trims ripped out, new switches installed and for what, I would,t fix the problem.

We should call it the green crusty test

Andy.MacFadyen wrote: We should call it the green crusty test

Agreed. Should be the new name for these forums.

Thanks for sharing, pictures and everything! Someone was just asking about using the Power Probe test leads with their meter. If I can find that thread I'll put a link to this one in there.

This is so true! Last night i was troubleshooting a machine with a solenoid malfunction, with a multitude of junction blocks, switches and exposed connectors. Using what i’ve learned i checked the circuit from point to point and found a 3,5v drop in an 18" long wire UNDER LOAD that was probably compromised from bending and aging (sounds like myself!).
If i had been just looking for heat or corrosion or any visual clues i’d still be working on this machine...

Hmmm. Well humans do conduct electricity. I'm feeling a little creaky these days, wonder what MY voltage drop is after a lifetime of bending and aging. Probably best not to do that test.