You need to look at the grounds at one of the rear sockets. Resistance at the grounds is putting the 2 lamps in series from the other bulbs giving you the half voltage causing the low current sensitivity of the LEDs to light up. 

Dennis

-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of Stuart MacMillan
Sent: Monday, April 10, 2017 9:09 PM
To: vanagon@GERRY.VANAGON.COM
Subject: Backup light puzzle anyone?

I got a pair of LED back up "bulbs" along with the other LEDs for my '85 automatic transmission Vanagon, and they are on all the time when ignition is on (other bulbs work fine). The switch on the selector is brand new (both parts), but there is a constant 5v at the backup lights and at the switched contact on the selector switch, and the proper 12 volts on the power side.
5v is enough to illuminate the LEDs.

There has to be some kind of short in the wiring between the switch and the lights, but where would that wire pick up 5 volts?  The rear taillight light assemblies are in excellent condition and I've re-done the ground at the left taillight.

I've had to go back to the filament bulbs until I can figure this one out.
Or maybe just forget about the LEDs because the short is probably buried somewhere in the wrapped harness under the van.

No end to the fun!

Stuart