Reverse Light Sw location E34 (Auto Trans) ('95 525i Wagon)

[HumanRoughDraft]

Anyone know where this is on the automatic transmission? My backup white lights don't work & I failed the Massachusetts Safety Inspection. I took off the shifter T knob and the wood plate and cannot find it there. Someone told me it was on the side of the tranny under the car on passenger side. I have the car on jacks now but still cannot find it.

The Fuse (F12) is has power to it. The wires in the trunk lid have 12vdc to it when reverse gear is engaged and 0vdc when taked out of reverse, yet they won't light up. This confused me. I took the bulbs out and tested them - they are ok. Back to the wireing - If they have 12v why won't they light up? Could it be that a digital volt meter (being sensitive) "senses" a trace of 12vdc running to it via a faulty switch (which I cannot find) but doesn't have enough AMPS to light it?

Any help would be appreciated - thanks

[Bill R.]

Anyone know where this is on the automatic transmission? My backup white lights don't work & I failed the Massachusetts Safety Inspection. I took off the shifter T knob and the wood plate and cannot find it there. Someone told me it was on the side of the tranny under the car on passenger side. I have the car on jacks now but still cannot find it.

The Fuse (F12) is has power to it. The wires in the trunk lid have 12vdc to it when reverse gear is engaged and 0vdc when taked out of reverse, yet they won't light up. This confused me. I took the bulbs out and tested them - they are ok. Back to the wireing - If they have 12v why won't they light up? Could it be that a digital volt meter (being sensitive) "senses" a trace of 12vdc running to it via a faulty switch (which I cannot find) but doesn't have enough AMPS to light it?

Any help would be appreciated - thanks

[mikell]

The Fuse (F12) is has power to it. The wires in the trunk lid have 12vdc to it when reverse gear is engaged and 0vdc when taked out of reverse, yet they won't light up. This confused me. I took the bulbs out and tested them - they are ok. Back to the wireing - If they have 12v why won't they light up? Could it be that a digital volt meter (being sensitive) "senses" a trace of 12vdc running to it via a faulty switch (which I cannot find) but doesn't have enough AMPS to light it?

If you're getting voltage at the lights at the proper time (when in reverse), then perhaps it's something besides the switch. Did you measure volts across the light socket, or between the hot lead and a ground - I'm thinking maybe the ground connection at the light is bad, or maybe the socket contacts are oxidized - try some contact cleaner or fine sandpaper to improve the connection.

Good luck.

[Bill R.]

be a poor ground since both rear lights are grounded at the same location. x493 as seen here under the rear seat is the ground for the back up lights.

If you're getting voltage at the lights at the proper time (when in reverse), then perhaps it's something besides the switch. Did you measure volts across the light socket, or between the hot lead and a ground - I'm thinking maybe the ground connection at the light is bad, or maybe the socket contacts are oxidized - try some contact cleaner or fine sandpaper to improve the connection.

Good luck.

[mikell]

Bill, you're bloody amazing!

BTW, where do you get stabilant 22 - I googled it and it looks like I can use some.

[HumanRoughDraft]

Now I am stumped. I Do have 12v at the blue(+) to Brown (-) Plug at trunk lid where it plugs into male recept. Also have 12v at the bulb recept. Did a hot wire from bulb to Blue and brown - nothing. I then crossed the blue and brown and got no sparks and yet I have 12vdc. I also shorted the blue to a known ground on the car and still no sparks and yet I still get 12vdc from Blue to ground.

I did notice that in order to get 12vdc on the volt meter I have to jiggle the Shift knob in and out of Reverse a few times in order for the Volt meter to stablize at 12.85 volts. (Key is in 2nd postion for powere to the circuit and also in order to unlok shift mechanism.

[mikell]

Maybe the switch is intermittent, after all. If you have volts and the lamp is not burned out, that should pass current, which heats the filament and makes light. I know of nothing in the circuit that would limit current if you have 12vdc present. Does it make a diff if the trunk is open or closed? Could it be that bad old trunk wire wear thing?
I assume that both lamps behave the same.
How about testing the switch with a continuity checker or ohm meter? Or, bypass the switch with a jumper and see if that gives good current to the lamps.
Good luck.

[HumanRoughDraft]

Maybe the switch is intermittent, after all. If you have volts and the lamp is not burned out, that should pass current, which heats the filament and makes light. I know of nothing in the circuit that would limit current if you have 12vdc present. Does it make a diff if the trunk is open or closed? Could it be that bad old trunk wire wear thing?
I assume that both lamps behave the same.
How about testing the switch with a continuity checker or ohm meter? Or, bypass the switch with a jumper and see if that gives good current to the lamps.
Good luck.

Yes Nxt thing to do is bypass switch which means I will simple cross the 2 wires going to the switch (If I can get to the Switch - as there are too many things in the way).

Thanks Mikell - you have been vry helpful as has Bill - Regards - Courtland

[HumanRoughDraft]

Anyone know if I can get to the switch from under the car or do I have to take apart the shift mechinism, etc, from inside the car? (Automatic Transmission)

[Javier]

is the same range switch (at the bottom of range selector shift lever), no extra switch in the gear as for manual models. Also, per my drawings, ground is different for right and left bulb in touring version. So there is some homework to do. You said there is 12 V at the bulb socket, Both sides? Have you checked continuity to ground from the other pin of the bulb socket?

To have 12 V at the socket is not enough if ground pad is opened (current should flow, it needs both connections, one to battery and one to ground.

A simple check is to connect to ground (with an extra wire) the brown wire coming out of the light assembly (both sides), if ground is missing, it should light up the bulb.

Also, if mirrors adjust (memory seats) when in reverse, switch is OK.

Javier