850 auto, starter engages whenever R is selected!

will-sussex-uk · Post by **will-sussex-uk** » 28 Mar 2011, 15:28

Hi all

hoping you can help.

Just bought a 1996 850 2.0 auto with 219,000 miles on it from some people who were going to scrap it, the garage told them it needed a new transmission because of a loud grating noise whenever you put it in reverse, so I bought it to break for parts but I found out the real problem is the starter is switching on everytime you go into reverse!

I thought this would be an internal fault in the inhibitor/reversing light switch so I removed the battery, airbox etc and took this off the trans and took it apart expecting to see bits of copper all over the place bridging two of the tracks but all looks good and having tried connecting only the reversing light contacts in the switch, the starter still kicks in meaning probably the fault must lie outside this switch. Switch appears to be part of a small loom which goes into a multiplug with metal retaining lever.

Anyone had this fault or know what all the wire colours or pin numbers are for this plug to help me trace the fault? If I knew which was the reversing lamps switch part I could maybe cut it to solve the problem if it becomes a case of scrap the car or live with no reversing lamps, that is unless I can find the short.

Presumably the other tracks in the switch tell the trans brain to keep car in low gear etc, and the mechanical connection to the gearbox only does reverse, drive neutral and park?

If anyone has heard of this fault and what the problem might be please reply. I have searched the net and found no reference to it.
Thanks
Will

Post by **precopster** » 28 Mar 2011, 15:36

The starter switch (part 9447803) itself is a source of many weird and wonderful problems. Our sponsors FCP Groton list them at about $50 but try a used one (even if it's worn it shouldn't have the same problem) Usually they cause no indicators, no dash lights and many other problems.

Backup light switch number is 9442728 ($15 from FCP)

will-sussex-uk · Post by **will-sussex-uk** » 28 Mar 2011, 15:45

thankyou but the ignition switch itself seems highly unlikely to be the culprit because how would it know I had put the car in reverse, there would be no connection from the reversing lamp circuit to that switch .

And the part number you have given for a reversing switch seems to be a normal switch like you would get on a manual transmission.

Thankyou for trying though.

Post by **precopster** » 28 Mar 2011, 16:03

All wiring diagrams are available from the Database-just hover your mouse over Repair Database.

"highly unlikely" is why you should try it as the other faults it creates come under the same category. There are around 8 terminals on this switch. Only four or five are needed for conventional ignition switches

Let us know how you go.

Post by **JDS60R** » 28 Mar 2011, 16:16

Disconnect starter trigger wire from ignition switch before putting in reverse. Monitor for voltage on trigger wire. Putting the trans in reverse causes two conditions. First as you stated the switch activates the backup lights. Second the engine/trans physically move ( due to engine running and toque being applied) . This second condition can cause the harness to move and can connect an otherwise un-found short.

By disconnecting the trigger wire at the ign switch , after car is started, you can determine if signal is coming through the ign switch or if there is a sort in the harness. Most of these that I have fixed come down to a bad car auto starter, a short in the harness or a bad ignition switch itself .

Wish I was there to help - these are my favorite types of problems.

will-sussex-uk · Post by **will-sussex-uk** » 28 Mar 2011, 16:28

I appreciate the speedy replies so far folks as I am working on the car right now and keep popping back in to check the forum.

Thankyou yes I'm normally pretty good at electrical gremlins myself, I've done EFI engine installs in custom cars etc.

This is why I've narrowed it down to a short between reversing lamps and starter. To be more specific it must be the output of the reversing lamps (to the lamps themselves) and the output of the inhibitor to starter circuit because the starter shouldn't even be allowed to come on in reverse with the key, let alone without even touching the key.

Its not a vibration issue because it does it even if engine not running. Short appears to be permenant, i've tried shaking various bits of harness then trying again.

I was going to disconnect starter solenoid wire and connect it to a bulb instead and go around tugging bits of harness to see if I get it to flicker or go out but the starter looks like a right mission to get to on this car.

Just downloaded diagram, Fantastic that you have the diagrams here!

Edit: Ok this is what I have tried just now.. disconnected range switch (inhibitor/reversing lamp sector switch on top of transmission) Removed back of plug to expose pins. Tested for reversing lamp power and starter trigger, all correct. but if I get a piece of wire and bridge the reversing light terminals simulating the reversing light portion of the switch operating,
( reversing input Blue Grey pin 9 and output Blue pin 5, the stater operates.
This completely eliminates this switch range from suspicion.

Going back out for another look.

will-sussex-uk · Post by **will-sussex-uk** » 28 Mar 2011, 19:28

Ok i think i have found it. Plastic conduit between radiator and starter motor, where looms merge, I just took the lid off, its quite oily so will clean it tomorrow and have a proper look but I think two wires have chafed through and are touching in there.

will-sussex-uk · Post by **will-sussex-uk** » 29 Mar 2011, 07:25

wires separated , fault cured.

hope this thread hopes someone else in future.