I recently replaced the factory Delco tape deck in my 1988 GMC
Suburban with a DIN-sized Sony model. The replacement tape deck works
beautifully, although installing it had the strange side-effect of
causing the parking/tail lights to stop functioning.

The brake lights, turn signals, and back-up lights work fine, but
there is no voltage at either of the tail lights or license plate
light (the bulbs are good). According to my Chilton book, the
tail/license plate lights are on the same circuit. I have verified
all fuses as good and that the brown +12V tail light wire in the light
switch has voltage when the lights are on.

The replacement stereo has no dimmer function, so the grey wire on the
original stereo wiring harness has been cut and taped off at the end.
The original wiring also included an auxillary plug with an orange and
brown wire, which seem to be +12V constant and another dimmer wire
accordingly. Again, I cut off and taped the brown dimmer wire
although I did wire the orange +12V constant wire into the replacement
unit. Disconnecting the replacement stereo does not fix the problem.

Although I find it hard to believe that GMC would make a vehicle this
way, is it at all possible that the original factory stereo was
somehow inline with the tailights, and that by my cutting the grey and
brown dimmer wires (both of which read +12V when the lights are on) I
effectively cut the taillight circuit? The only other thing I can
think of is that during the installation I might have bumped a
connector loose.

Thanks in advance for any help or suggestions,

Nick

Nick Pelis wrote:

The brake lights, turn signals, and back-up lights work fine, but
there is no voltage at either of the tail lights or license plate
light (the bulbs are good). According to my Chilton book, the
tail/license plate lights are on the same circuit. I have verified
all fuses as good and that the brown +12V tail light wire in the light
switch has voltage when the lights are on.

The replacement stereo has no dimmer function, so the grey wire on the
original stereo wiring harness has been cut and taped off at the end.
The original wiring also included an auxillary plug with an orange and
brown wire, which seem to be +12V constant and another dimmer wire
accordingly. Again, I cut off and taped the brown dimmer wire
although I did wire the orange +12V constant wire into the replacement
unit. Disconnecting the replacement stereo does not fix the problem.

Although I find it hard to believe that GMC would make a vehicle this
way, is it at all possible that the original factory stereo was
somehow inline with the tailights, and that by my cutting the grey and
brown dimmer wires (both of which read +12V when the lights are on) I
effectively cut the taillight circuit? The only other thing I can
think of is that during the installation I might have bumped a
connector loose.

No. In fact, the only thing your headunit has incommon with your tail
lights is that they are both fed voltage through lighting switch on the
dashboard. The brown wire is the dashboard illumination circuit, the
grey wire is the dimmer wire. You'll find both of these wires in the
same plug on the back of the lightswitch that the parking lights are on.

Scenario 1) The harness was pulled off of the back of the light switch,
even if only partially. This would have required the effort of several
neanderthals working in unison, some pulling at the gray and brown
wires, while others beat on the dash with the thigh bone of a wooly
mammoth. Had this been done by a professional installer, I'd say that
this is exactly what happenned. Just sqeeze your hand up under the dash
(like delivering a calve from a cow made of sharp steel scews) and push
all the plugs firmly in place (there's about three).

Scenario 2)(AKA the "please god let it be this one" scenario) You blew a
different fuse. GM thinks its freaking cute to have one fuse labelled
for one item, but actually control five or six different things
(example: "CTSY LIGHTS" also feeds the cigarette lighter and the radios
memory feed). They seem equally amused in the notion of labelling a fuse
in such a way as you'd *think* it controlled one thing, but in fact it
controls something completely unrelated (on my Pontiac, BLNKR is the
fuse for the hazard lights, and not the turn signal). It's really best
to just pull and check every damn fuse with a DMM while wiggling the
blades. These clever little buggers can sometimes blow in a hairline
fracture, so that anyone would look at it and say "yeah, it's okay", but
in fact its an open circuit. Replace any suspect fuses.

Scenario 3) Something got fried, and it ain't the chitlins. There are
actually two brown wires that go into the back of that switch - one
feeds the dashboard illumination circuit (that brown wire is part of
that), the other feeds the parking light circuit. One is a differnt
brown, and might even be confused for black in the wrong lighting. If
this wire doesn't put out, just threaten to not take it to the prom. If
that doesn't work, you can cut the parking light wire, and solder the
parking light side to the headlight output wire (which I think is
white). Or you can buy a new switch if you've got $90 burning a hole in
your checkbook.

Good luck!

--
thelizman "I didn't steal the FAQ either"

Before you ask a question, check the FAQs for this newsgroup at
http://www.mobileaudio.com/rac-faq. It contains over a decade and
a half of knowledge.

teamROCS Car Audio Forums http://www.teamrocs.com/caraudio/
teamROCS Car Audio News http://www.teamrocs.com/news/
"It's about the music, stupid"

This post is Copyright (C) 2004. Reproduction of its content anywhere
other than usenet without the express written permission of the author
is forbidden.

99% of the time someone has this problem it's either they used the dash
light wire for a ground or they accidentaly shorted it to ground blowing the
tail lamp fuse. Do the dash lights work? Do the parking lamps on the front
of the truck come on? If not, check for a blown fuse. If the dash lights
work, pull a tail lamp bulb and check for voltage with a DMM, if you have
voltage there then look for an open ground to the tail lamp harness. Could
have been a coincidence they quit then if the ground for the lamp harness
came loose.

--
Jammy Harbin
J & J Electronics, Inc.
227 S. 4th St.
Selmer, TN 38375
731-645-3311
"Nick Pelis" wrote in message
m...
I recently replaced the factory Delco tape deck in my 1988 GMC
Suburban with a DIN-sized Sony model. The replacement tape deck works
beautifully, although installing it had the strange side-effect of
causing the parking/tail lights to stop functioning.

The brake lights, turn signals, and back-up lights work fine, but
there is no voltage at either of the tail lights or license plate
light (the bulbs are good). According to my Chilton book, the
tail/license plate lights are on the same circuit. I have verified
all fuses as good and that the brown +12V tail light wire in the light
switch has voltage when the lights are on.

The replacement stereo has no dimmer function, so the grey wire on the
original stereo wiring harness has been cut and taped off at the end.
The original wiring also included an auxillary plug with an orange and
brown wire, which seem to be +12V constant and another dimmer wire
accordingly. Again, I cut off and taped the brown dimmer wire
although I did wire the orange +12V constant wire into the replacement
unit. Disconnecting the replacement stereo does not fix the problem.

Although I find it hard to believe that GMC would make a vehicle this
way, is it at all possible that the original factory stereo was
somehow inline with the tailights, and that by my cutting the grey and
brown dimmer wires (both of which read +12V when the lights are on) I
effectively cut the taillight circuit? The only other thing I can
think of is that during the installation I might have bumped a
connector loose.

Thanks in advance for any help or suggestions,

Nick

Well, I finally figured it out--thanks everyone for your help. After
pulling the "CRTSY LGHTS" fuse and wriggling the fuse blades around,
my meter was reporting intermittent connectivity. Replacing the fuse
restored both the dash lights and the buzzer that sounds when the
lights are on, but the taillights were still out.

I knew it had to be a wiring problem at this point since half of the
taillight circuit was working. After establishing that there was
power at the trailer hookup on the back but not at the actual sockets
in the tailight fixture, I removed the bulbs and checked them by
jumpering them directly across the battery terminals. The bulbs were
good, so I climbed underneath the car and discovered that the wiring
which goes from the fuel tank in the center to both taillights was
broken, and the insulation was strangely pitted and corroded. I
yanked out all of the original factory wiring and replaced it with a
roll of trailer wire I got at auto zone for $2.50, and now every
combination of brake, turn, and tail lights works wonderfully.
Strange as it seems, the only explanation I can think of is that the
age of the original factory wiring (1988) coupled with this new
corrosive chemical they've been putting on the road to melt winter
snow caused the wires to literally fall apart.

Thanks again!