I just discovered something really weird.
I have been adding some lights to my new (used) Jeep Wrangler.
The first thing I discovered is that buying small rolls of colored wiring is really expensive - it is almost $13 for a 20' roll of 14 gauge, and I wanted 4 different colors. I discovered Harbor Freight has a wiring harness for trailers that is 25' long for $13.99 and it has red, yellow, green, brown and white - 125' of wire! You can split the wires as needed - I ran the red/yellow to the rear of the Jeep and the brown/green to the front, and I pulled off the white for use on another project someday.
https://www.harborfreight.com/four-way-trailer-wiring-connection-kit-25-ft-64... I installed a Lasfit control panel that had 4 switches and a relay box. The relay box wires extended to the right front frame rail at the firewall, and I used the new wires to extend the wires to reach the front/rear bumpers. When I attached my new wires to the wires coming from the relay box I stripped and soldered the wires together - I didn't have any heat shrink tubing so I cut a 1.5" piece of rubber vacuum hose glued in place with some RTV silicone to protect the bare wire in the soldered splice. I then wrapped both splices together with electrical tape and ran the wires through the frame rail (one pair to the front and one pair to the rear).
Everything seemed just fine and I connected a set of white LED modular lights in the rear to use as backup lights. When I pushed button II on the bottom row of the switch panel the white lights came on.
A few days later I installed RED led emergency beacon lights on the rear. My intent for them is to use them in the "steady on" mode in foggy conditions, and use the "strobe" function for emergencies. When I got them installed and connected to switch IV in the bottom row - the red lights came on.......but so did the white lights! When I pushed switch II in the lower panel the white lights came on - but so did the red lights!
When the either lower switch was pushed ON - both lights would come on. The light corresponding to the switch was just a bit brighter than the other light - at first I believed I may have a ground issue. After checking the grounds and running a jumper ground wire nothing changed and that evidently was not the issue.
The upper row switches (I & IV) ran to the front of the Jeep and were not yet connected to anything. When I hooked up a volt meter I discovered that with the switches OFF there was no power to either wire (like is should be) - but when I pushed either switch to ON I got 12V to both wires! Both the front and rear wires were activating the pair when any single switch was activated - however the rear wires did not activate the front, and similarly the front switches did not activate the rear.
I decided I would go to the connections I had made at the Lasfit relay box wiring and my trailer wire extensions.......could the Harbor Freight wire insulation be faulty? I pulled out the spliced connections that were insulated with rubber vacuum tube, and I first cut off the electrical tape that was holding the splices together - and the wires worked as normal! Once the rubber vacuum tube was not touching each other the wires did not pass power across them!!!!!
It turns out the rubber vacuum tube is conductive and was passing voltage across the soldered connections! I cut off the tubing and cleaned up the soldered joint, then applied liquid rubber insulation and silicone bonding electrical tape. The wiring now works as it should. (Good thing I had wrapped the tubing splice with electrical tape or it might have passed voltage to the frame!).
So - don't use rubber vacuum line as electrical insulation.....turns out the darn stuff passes electricity nearly as well as it passes air!!!
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