Car: 1995 Saturn SL1 SOHC.

Symptom: Both reverse/back-up lights do not turn on when in reverse gear.


My troubleshooting: From reading my Haynes manual.... I located the
Back-up Light Switch on top of the manual transaxle.
1. The Back-up Light fuse is good.
2. Bulbs test fine.
3. There is circuit continuity between Back-up Light fuse (at front
engine fuse box) and lamps and also from the Back-up Light fuse and the
right contact of the switch plug (view w/ clip @ top).
4. With ignition ON (engine not running) I read 12.7V at the right
terminal of the Back-up Light fuse. In this state I read only 60mV at
the right contact of the switch plug and the lamp terminal with the bulb
removed.
5. Wires and Wire-harness look in good shape.

From the circuit diagram I should be reading Voltage on the battery
side of the switch connector, then also on the ground side of the switch
when in reverse if the switch is good. Right now it seems that I cannot
conclude that the switch is bad by testing it properly. This looks to be
a simple bulb circuit, power is switched ON/OFF by the transmission
(manual) Backup switch alone.... am I correct?


*from a suggestion on another forum....
Is this a feasible way to troubleshoot this circuit? Because I'm getting
no light but have continuity, I wonder there is some other component in
the circuit.....
With ignition key OFF, I unplugged the 2-wire connector from the switch,
closed (short w/ wire) the circuit on both terminals of the
connector.... turned ON ignition key.... still no light, also ran
engine.... still no light.

The bulbs are type 1157. These have two filaments/terminals, but I
notice that the sockets only have one positive terminal, I assume ground
is in a connection to the base body. The sockets are keyed, nothing
looks physically broken.

It looks that if I'd replace the switch the problem would not be solved.


Any thoughts? Thanks very much for your assistance, much appreciated.
Cheers, Roger

Roger,

I have never had a problem with that circuit, but your troubleshooting logic
seems sound and the single wire to the bulbs infers a chassis ground to
complete the circuit (make sure the grounds are good and not rusted). That
said, I do have some questions though that may help shed some light here:

Are you sure you have the correct fuse? (IMO Haynes is not a very good
source to guarantee this is the correct one).

How are you measuring connectivity from the top of the reverse light switch
to the "top" of the fuse?

When you measure 12.7V at the "right" terminal of the back up light fuse,
what do you read on the left terminal (this assumes the fuse is in the
circuit)?

Are there two gear selector driven electrical switches (one for
parking/neutral safety interlock and another for the reverse lights) or just
one and if so, are you on the correct one?

Are there any other symptoms/non-working electrical systems?

Do the reverse lights flash at all, even for a brief moment when the gear
selector is moved through all the gears from park and back? (Safety first -
This takes a second person inside the vehicle to see what is actually
happening outside.)

What voltage to chassis ground do you measure on the input to the reverse
switch when the ignition is switched "on"?

Bob


"Roger E" <rogerehrl (AT) yahoo (DOT) ca> wrote

Hi Bob

Thank you very much for your reply, much appreciated. Sorry I did not
reply sooner, I had to find some time to look at the circuit again. I'll
answer your questions below....

Bob Shuman wrote:
The socket single contact looks fine, no corrosion, but I'm looking for
the 2nd contact (ground), it may be recessed in the sleeve or the 2 key
notches may act as this terminal. I looked on the net for the 1157 bulb
specs... found them but no specific details confirming the common ground
electrical connection. All the bulb sockets are lined with a cream
inside, (original).


Yes, 10A fuse, also labeled as such on the fusebox cover. Fuse is good.


I removed the switch plug/connector and inserted a 22 AWG wire into each
terminal of this plug.... one at a time .... used this as one circuit
node and the other at the terminal socket for the fuse in the fusebox
(fuse out), and checked electrical continuity.


No I had the fuse out (open circuit), the left terminal reads 0V.....
ignition ON (engine not running).

Only one switch. On the top/back end of the manual transaxle.... also
referenced in Haynes manual.


No other electrical problems/symptoms.


No flash or light at all. I opened the rear lamp case on each side,
removed the backup lamp socket, and rested it with the bulb in on the
case peeking out along the side of the car so that I could notice any
light as I watched in the mirrors when shifting to reverse.

Only about 60mV, not zero....

I examined both 1157 bulb's sockets again. They are coated with a
anti-corrosion cream on the inside. I also notice on both left and right
sockets that the ground terminal, a flat metal prong is recessed
somewhat, not touching the brass cylinder case of the bulb. It is also
situated higher up at the point where the brass cylinder case ends and
the glass of the bulb begins. There definitely is no electrical contact
here on both Lt & Rt sockets. It appears that this may have been the
design during manufacture. Strange then were exactly is the ground
terminal? I also sprayed contact cleaner into both sockets. The
terminals are free of oxidation.


Thanks, Roger

Roger,

The 1157 is a two filament, 3 conductor/contact bulb that has been around
for many, many years. It is usually used for a combined turn
indicator/brake light function. Are you sure this is the correct bulb
number and does it have 3 contacts (two soldered dimple contacts on the base
and a brass base for the common/shared ground)? I would have expected you
would have found a two contact, single filament 1156 bulb for the back up
lights. BTW, The anti-corrosion grease used in the socket is normal, but
the contacts from the socket should make good physical/electrical connection
with all 3 of the bulb's contacts. That all said, it doesn't seem likely
that both contacts in both sockets have connectivity issues and this is why
I had suggested that you make sure the grounds are there to both sockets (I
assumed they may share a common lead and physical connection to the
chassis).

I'd suggest that you measure the resistance from the ground pin of the
socket to the vehicle chassis. You should see roughly an ohm or less of
resistance from both of these contacts ion the sockets.

Also, please re-verify you are looking at the right sockets and have the
correct bulb number. Is it possible that a previous owner put in 2 of the
wrong bulbs? How many contacts are in the socket and do they match the
bulb?

I have other questions as well on the reverse light gear selector switch
too. I really would expect there to be two switches: one for the reverse
lights and another for the starter safety interlock (park/neutral) switch.
I'd expect these to both go "hot" (12V) as soon as the ignition gets
switched on. If there is truly just one switch, then I'd also expect to see
more than one output from that switch since it needs to validate that the
vehicle is in either park or neutral to start as well as light the reverse
lights when in reverse. If you can get a copy of the schematic and trace the
circuit from the fuse box where you see the 12V through to one of the
reverse bulbs that would be the best way to troubleshoot this issue.

At this point there is too much apparently conflicting information in what
you have shared thus far for me to try to troubleshoot this remotely.

Bob


"Roger E" <rogerehrl (AT) yahoo (DOT) ca> wrote