1995 Saturn SL1 reverse/back-up lights & switch - resolved thanks

Thanks Bob & Folks

My problem with the reverse/back-up lights switch is resolved. I was
examining the wrong switch to be honest. There are two sensors that
appear similar on my manual transaxle case. One sensor (2 wire) is near
the back, which I saw when looking from underneath the car. The other
sensor (also 2 wire) I noticed later is on the top of the transaxle near
the dip stick, but somewhat hidden from view by the components over it.
The tests I mentioned below in previous posts were on the lower sensor
underneath the car. Saturn tells me that this is actually a speed
sensor..... I found the other sensor later and it is indeed the backup
lamp switch. I repeated the tests on it and everything measured as
expected. Also shorting this switch did keep the lamps on with the
ignition on. I see no parking/neutral safety interlock switch though.

I did buy a replacement backup lamp switch from Saturn ($14) and
replaced it myself.... bingo.... backup lamps work correctly now.

Cheers, Roger




1995 Saturn SL1 reverse/back-up lights & switch

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

Thanks very much for your assistance, much appreciated.
Cheers, Roger


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....

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



Author: Bob Shuman
Date: Sep 3, 2008 08:11
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,

Congratulations on the fix and saving yourself a lot of $ by diagnosing and
fixing it yourself! Thanks for closing out the thread and letting us know
how it worked out.

Bob