Run dedicated ground wires for each light then, if you can... I've looked at
the taillights on my 960 maybe twice, and I didn't get a good look at how
the power rails were done, but it looked like it was possible from what I
can remember... A 960 wagon has the same taillights as a 740, so it should
be similar. I remember metal posts, where spade connectors could just plug
right into (had to fix the taps for our trailers wiring harness...
indicators weren't working, one lead fell off after 11 years) - you might
have to cut the common negative rail, if there is one... Check connections,
and check for appropriate signals from the positive wires first though,
could just be a bad connection. (Check for a constant 12V for the running
lights, a flashing 12V for the turn signal, a solid 12V for the brakes, when
applied, a solid 12V for the reverse, when in gear, and a solid 12V for the
fog lamp/s when on).
I wouldn't use a diode to prevent a problem like that - because it means
there is an actual problem with the wiring - Sounds like one wire is
damaged, so the current is tracking back thru another one of your lights to
find a path to "ground" (there's no real ground on a car... it's all direct
current... positive and negative... Volvo's should be chassis <ground>
"Jim Corey" <email@example.com> wrote in message
> As I posted earlier, my 86 740 GLE, which I've owned since new, (350k
> miles) was rear ended. From insurance standpoint, totaled. After much
> back and forth, got enough to repaint the car (only MAACO), and buy a
> porta-power to do the body work prior to painting. (And to cover the costs
> of replacement taillights both sides, which I had on the shelf from an
> earlier e-bay purchase). About six hours work for son-in-law and I, and we
> were done. Car is finished, and looks quite nice.
> However, the car failed state light inspection (required when
> reregistering a "totaled" car). The brake-taillights, passenger side,
> where intermittent. No problem, thinks I. Probably too hasty in my
> reinstallation following the painting. After 2 hours, I couldn't isolate
> a ghost ground. The brake lights were grounding through the taillights.
> After fighting the problem, I threw a diode in the taillight lead, and
> VIOLA!!, problem solved.
> So now Victoria, our 740, will be good for another 350k (or at least
> outlast our S80!!)>