reversing lights

[porschedavid]

1986 porsche 928 s2
reversing lights dont come on when put in reverse (Auto gearbox)
fuse ok relay ok.
if i bypass relay they come on but stay on.

[harborman]

Did you check the back up light switch on the transmission?

[porschedavid]

dont seem to get a live going to auto box,when i bypass relay reverse lights come on

[harborman]

Originally Posted by porschedavid

dont seem to get a live going to auto box,when i bypass relay reverse lights come on

Is the relay coil getting power? Trace connections from relay coil to Trans switch. I am guessing since I have not looked at a schematic. What if you jumper the trans switch with relay in place?

[porschedavid]

ive got no power to any of the wires in that are spare tyre well.changed relay made no differents.

[harborman]

Originally Posted by porschedavid

ive got no power to any of the wires in that are spare tyre well.changed relay made no differents.

Back up relay is XXII
Pin 85 is ground
Pin 86 Goes to Starter lock out/ back up SW
Pin 87 to back up lamp SW then to back up lights
Pin 30 to Fuse

I hope this is correct, evidently two switches involved.

[porschedavid]

hi
if i join pin 30 to pin87 with a bit of wire lights come on, were does pin 86 go .does it go to rear spare wheel well,because i have no live on any wires there,so there for no live to switch on auto box i assume.Thanks for your help.

[harborman]

Originally Posted by porschedavid

hi
if i join pin 30 to pin87 with a bit of wire lights come on, were does pin 86 go .does it go to rear spare wheel well,because i have no live on any wires there,so there for no live to switch on auto box i assume.Thanks for your help.

Pin 86 goes to the lock out switch.

https://rennlist.com/forums/928-forum/963712-auto-trans-lockout-switch-differences.html

[porschedavid]

hi again
if pin 86 goes to switch on gearbox would i not have a live on one of the wires in spare wheel well,otherwise where does switch get its live from.thanks

[porschedavid]

when relay is in is pin 86 live to box,because mine is not

[harborman]

Originally Posted by porschedavid

when relay is in is pin 86 live to box,because mine is not

It appears the relay is getting it's power through the starter/lock out switch. The switch does other functions one of which is the back up lights. You will have to check that switch and see if it operating properly. When in the back up position it should provide power to the back up relay coil.

[harborman]

Originally Posted by porschedavid

when relay is in is pin 86 live to box,because mine is not

Pin 86 will only have power on it when the start/back up switch is in the back up position. If you have no power in that position, then the start/back up switch might be defective or it is not getting power to provide to the relay coil. Since you did jumper the relay and the back up lights came on, your problem is the relay, not getting power to the coil from the start/back up switch. So you need to investigate that switch.

[porschedavid]

hi
where does switch on box gets its power from to go back to relay.should i not have live in rear well going to switch on box,because all wires are not live there .I thought you should have live going to switch and from switch back to relay live if switch works ok course

[harborman]

Originally Posted by porschedavid

hi
where does switch on box gets its power from to go back to relay.should i not have live in rear well going to switch on box,because all wires are not live there .I thought you should have live going to switch and from switch back to relay live if switch works ok course

Did you check the leads on the starter/lock out switch? Are any hot?

[harborman]

Lets see if this helps and my drawings match your car.

Looks like a 9 pin connector goes to the starter/lock out switch.

5 of the pins go to your gear indicators P,N,D,3,2

2 pins are switched for backup lights. (switches power to pin 86 of the relay coil)
Looks like one wire is grey/yellow going to pin 86 or the backup light relay
The other lead is yellow/red which might be the hot lead to this switch & Gear indicators.

2 pins are for another switch. (lock out for starter)

So do your gear indicator lights work as this look like the same power lead going to the switch for the back up relay.

[porschedavid]

No hot wires on switch on gearbox.indicator lights all work apart from P and R i assume bulb blown.Cant work out why no hot wire to switch on gearbox

[harborman]

Originally Posted by porschedavid

No hot wires on switch on gearbox.indicator lights all work apart from P and R i assume bulb blown.Cant work out why no hot wire to switch on gearbox

From the diagram I have, the gear light indicators power is applied with the switch. I suspect your starter/lock out switch has a detective switch inside. What I am saying is, the same wire that provides power to the gear indicators also provides it to the backup light switch inside the Starter/lock out assembly. Check that yellow/red wire for power. Pins 5 & 6 switch the back up light relay. Pin 5 should have power on it. Putting a jumper on pin 5 to 6 should operate your back up light relay XXII.

[porschedavid]

Do you know which pins are 5 and 6

[harborman]

Originally Posted by porschedavid

Do you know which pins are 5 and 6

Sorry, I can't help you on that. Find the yellow/red wire in the cable, that should be pin 5.

[porschedavid]

HI
I think switch is the problem.Any ideas on change it.i know it just an bolts but more worryed about setting it up in right place.Thanks for all your helP last few days.
(YOU ARE A TOP GUY)