Firstly the rear light clusters do not have a wired ground to the rear
number plate bolts (or anything else) on any year, they rely on the physical
fixings. Secondly if this is bad the tail light will 'see' the ground on
the other light unit via the two stop light filaments and the ground to the
front indicators via the two turn signal filaments. This means that any
single light will work satisfactorily, although possibly a little dimly, but
when you start using combinations of lights things start going out and
lighting up all over the place. Also if both tail lights are going out you
can forget the light units themselves because of the individual grounds. A
76 has a 4-way fusebox and the top two fuses power the parking lights, one
per side. because of this there are separate wires and connectors from the
fusebox to each corner of the car, so if both sides are going out you can
forget these as well. For both sides to go out it must he common, so the
problem must be from the red/green from the fusebox back towards the main
lighting switch. This would affect the front parking lights as well, but as
these are inside the headlights you won't know they have failed if the
headlights are on. So the first thing is to firmly establish exactly which
lights aren't on and confirm that both sides at the rear really are failing,
by getting out and having a look, not relying on random reflections. After
that intermittent failures are problematic, you just have to wait until the
fault is present before a voltmeter will tell you much.
Another point to bear in mind that with the original turn flasher fitted if
one turn light has failed the flashers that side will only light, they won't
flash, and this is clearly visible on the dash tell-tales and audibly. Even
if a proper aftermarket flasher has been fitted a failed bulb will result in
flashing at double-speed, again clear audibly and visibly. Only if a hazard
flasher, or an incorrect aftermarket turn flasher has been fitted, will the
turn flashers flash at a constant speed even with one corner out, and this
is very dangerous.
PaulH.
----- Original Message -----
From: "Scott Regel" <Scott.Regel@dpra.com>
To: <mgs@autox.team.net>
Sent: Tuesday, December 23, 2003 3:02 PM
Subject: Rear tail lights not working again/wiring 101
> ... I have
> a 76 B that seems to suffer from chronic lack of rear lights. The brake
> lights work, headlights work...I'm not sure about the rear turn signal.
> But this seems to happen all the time. I've cleaned the connectors,
> fuse box, giggled and wiggled wires too. It will sometimes just start
> working again and then stop.
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