Odd electrical issue-3 of 4 running lights work. 4th is sparky

[josborn10]

Hello,

I inherited a partially diagnosed electrical issue on a 74 911. With the headlights on - here is what I know so far, when I reconnect the red round wire at the battery, I get an exciting spark but the two front and right rear running lights come on. The left rear does not. All of the wires around and within the housing seem fine.

There is a pair of orange wires that come from that junction but they are capped. I assume if I left the red wire attached at the battery, the battery would drain quickly. I have looked around the engine and cargo compartments and I am not seeing any suspicious wiring issues. Given the size of the spark, I am assuming I have a ground fault.

Does anyone have any suggestions on where to look or the likely cause? Thanks in advance.

John

[86 911 Targa]

Originally Posted by josborn10

Hello,

I inherited a partially diagnosed electrical issue on a 74 911. With the headlights on - here is what I know so far, when I reconnect the red round wire at the battery, I get an exciting spark but the two front and right rear running lights come on. The left rear does not. All of the wires around and within the housing seem fine.

There is a pair of orange wires that come from that junction but they are capped. I assume if I left the red wire attached at the battery, the battery would drain quickly. I have looked around the engine and cargo compartments and I am not seeing any suspicious wiring issues. Given the size of the spark, I am assuming I have a ground fault.

Does anyone have any suggestions on where to look or the likely cause? Thanks in advance.

John

John,

Which junction?

The spark can be attributed to any electrical item which is in the "active" mode.

Radio, trunk light ect........

Not sure if Bentley has a manual for your M/Y.

Try this:

Manuals

And good luck,

Gerry

[DRACO A5OG]

Hey John,

Congrats on your new to you 911.

When you say the wires looked good, did you actually open up the light assembly. It requires you to remove the lens & housing from the car and crack open the back to see several PCB board type components and wires rivetted on them and a ground on the housing itself.

I had a severe short where my hot lead was touch the housing due to a cracked PCB board from POs forcing the blubs in thinking it would make a better contact, not. It burned out my Brake Light Switches.




Socket was also loose on mine and I used a ratchet extension and mallot to smash it tight.

Each PCB type board should be intact and not crack or worse broken, if broken you can JB weld them or replace the PCB board and solder or rivet the wires back on.

Jim

Just a side note, you probably know this, but in our negative ground system, you want to connect the Power (RED) Connection then the Negative (BLACK) Connection on the battery, A so slight spark from negative will not harm you, the clock draws power if still working.

[josborn10]

Hello Gerry,

I agree that there is a fault but I am trying to see the link between the rear tail light being out and the sparks at the battery. I am hoping to avoid running every whirr from the fuse box by hand. I appreciate your suggestion.

Hello Jim,

I did pull of the back of the housing. Everything looked secure, no loose wires or burn marks. Thanks for the heads up.

Perhaps I am dealing with two separate issues?

John

[josborn10]

Gentlemen,

Quick update, you were both correct. I removed the aftermarket wiring fro the stereo from the fuse box and the shocking went away. When I wiggled the bulb in the housing, the light came on. I have a cache of different bulbs and used one the fit snug and it worked.

Thank you for taking time to help. This is an amazing forum. I hope I can offer help one day and not just ask. Again, thank you.

John

[DRACO A5OG]

Oh great!

I'm sure you sir, I'm sure you will.

So do you have the Pelican Statutory picture of your new baby???