Series 2 rear light mystery

Lucas has struck again ...... I seem to have a short between the running light circuit and the reverse lights...... If I shift into reverse with no lights on, getting back up (white) and tail lights on...... or if dash toggle set to running lights, then back up lights also come on along with tails...... turn signals working fine....brake lights working when the pressure switch feels like it (see other post)... I suspect short between the reverse & rear tail +12V lines.... or perhaps some weird floating ground creating some strange current loop .......... Any debug ideas?

Was thinking to unhook the back lights and reconnect one at a time (both back up, both tail lights), also to volt meter the open leads and inspect / clean the ground connections....... I dont think it is dash toggle as that has nothing to do with the reverse lights (or it shouldn't).

Any one else seen this or have recommended debug ideas?
Thanks!
Cali Bugeye

I would look at the earths 1st.

If you remove the bulb from reverse for instance and put in reverse and recheck:
fault on tail, still there its probably a short on the feed
no fault, probably bad earth.

If the brake lights dont make the reverse light come on then I would have though it more likely a feed short somewhere.

Hi - does looks to be a feed short some where - spent this afternoon shinning up and cleaning the various contacts and ground barrel connections. Error still occurring. Reverse gear will light white and all running lights...... And turning on the running lights lights the four running lights and the two back up lights..... I peeked behind the dash, and I dont think it can be there as the back up lead should start from the gear box switch and head back per schematic. I found a rats nest of wires and a gunk'ed up barrier strip in the back wheel well (right side) which tees the cables from the main harness to both sides lamp area..... I suspect a short in there between the Back Up and Tail circuits on the +12 line....... More to debug there next........ I will post my progress. For now,. removed the back up bulbs.

Other progress today, installed a new washer hose - the spray works again!
Thanks for the advise......