...more electrical questions

[TWJ]

I'm still working on trying to resolve my "no blinkers, brake lights or backup lights" problem on my '72 T...

Using a voltmeter I tested voltage to the fuses in the #1 (top) fuse box with the following results:

-With the key off only fuses 1 & 2 had power.

-With the key in the no. 1 position fuses 1,2,4,5 & 6 had power.

Questions:

Does the above results seem correct?

Since the no. 8 fuse is for the blinkers, brake lights or backup lights (where my problem is) shouldn't it have power even if the key is off? OR???

If there is a grounding problem, say in the tail lights, would this cause the fuse to show no power (key on or off)?

Does this tell me anything else?

Does anyone have a chart showing what each fuse in the top box is for? My is missing from the cover.


Thanks Much!

[maxman]

What car do you have?

If it's an SC, i'd be happy to pull up my wiring diagrams and talk you though some of the troubleshooting. Perhaps I can be of a little help with a Carrera.

Let me know.

~Max

[TWJ]

Maxman,

The car is a '72 911T, mostly stock and it pretty nice condition. The wiring diagrams are on our host website in the "Tech Info Center".

I've had some great input from other posts but I still haven't resolved the problem.

[maxman]

I see now you have a '72.

Did you see the diagrams for you car on this page?

I'll send you a message with my phone # if you'd like some helping figuring out the current flow and a troubleshooting plan.

~Max

[HarryD]

Originally Posted by TWJ

I'm still working on trying to resolve my "no blinkers, brake lights or backup lights" problem on my '72 T...

Using a voltmeter I tested voltage to the fuses in the #1 (top) fuse box with the following results:

-With the key off only fuses 1 & 2 had power.

-With the key in the no. 1 position fuses 1,2,4,5 & 6 had power.

Questions:

Does the above results seem correct?

Since the no. 8 fuse is for the blinkers, brake lights or backup lights (where my problem is) shouldn't it have power even if the key is off? OR???

If there is a grounding problem, say in the tail lights, would this cause the fuse to show no power (key on or off)?

Does this tell me anything else?

Does anyone have a chart showing what each fuse in the top box is for? My is missing from the cover.


Thanks Much!

The legends for the wiring diagrams provide this information. The are two diagrams for the compelte wiring. You can access the diagrams and legends here:

Pelican Parts - Porsche 911 Parts Listings & Diagrams

I would suggest you print out each diagram to fill a 11x17 (or larger sheet) and use several colors of highlighters to trace the circuits you have concerns with.

Please note that sometimes a wire will end in "space" with a number. You will find the same number on the other sheet to continue the circuit.

[T77911S]

no, not really.

as long as the fuse at least has power with the key on, the lights should work. if not, i would check the switches: brake, backup, and turn sw. also check connectors, grounds. make sure the wires at the fuse are making good contact with the terminals. remove the wires and clean with a wire brush.

looks like power goes from 8 to 33 (emergency flasher?), then to 48 (flasher relay?), then out blu to the speedo and the turn signal bulbs, then to the markers and to the turn sw, from the SW back to 33 and back to 48, the flasher. the flasher has a voltage devider in there. all it does it open and close a relay, putting power on the and off the blu wire. strange they tied the alt light into all this.

then to fuses 9 and 10 for the rear and thru for the fronts. look for common points. if the rears work, look at fuses 9 and 10, if none work, look at 33, 48 and the turn switch. also the speedo and the blu wire.

notice the L and R in the speedo are backwards at the light switch.

wow, this vertigo has my head messed up. i had to go thru this thing several times to get it.

[sparkle84]

I didn't see anything mentioned about the front blinkers. If they work & all your problems are in the rear & the fuses & relays check out ok it's probably a ground problem. Light problems in older 911's are grounding problems 90% of the time. They're notorious for that. Particularly when more than one component doesn't work or starts doing strange things. I owned a '70T for 10 yrs. & every time there was a light problem (a lot ) it was related to the grounds. The rear assemblies are the worst. If u haven't done so u need to take the rear cover off the housing & check everything inside. These things need a strong ground or problems arise. My rear lights started doing wacky things in my SC ( same housings ) even though the grounds seemed ok. After trying everything with no results I finally ran a separate ground wire from the housing (not the back cover) to the body connection. Problem solved. Drilled thru the housing & ran a sheet metal screw thru to attach the wire. You could just sand an area & hold a wire firmly against it for a test & see what happens. Take 2 min. just to make sure if it's a ground problem. If it was a short you'd most likely have had blown fuses.

Good Luck

[ossiblue]

Originally Posted by TWJ

I'm still working on trying to resolve my "no blinkers, brake lights or backup lights" problem on my '72 T...

Using a voltmeter I tested voltage to the fuses in the #1 (top) fuse box with the following results:

-With the key off only fuses 1 & 2 had power.

-With the key in the no. 1 position fuses 1,2,4,5 & 6 had power.

Questions:

Does the above results seem correct?

Since the no. 8 fuse is for the blinkers, brake lights or backup lights (where my problem is) shouldn't it have power even if the key is off? OR???

If there is a grounding problem, say in the tail lights, would this cause the fuse to show no power (key on or off)?

Does this tell me anything else?

Does anyone have a chart showing what each fuse in the top box is for? My is missing from the cover.


Thanks Much!

How are you testing voltage to the fuses? Are you putting your meter on the line (feed) side of the fuse, the load side (to the devices), or to each side separately?

Fuse 8 is fed power by the link with fuse 7 which is hidden behind the fuse block. Fuse 7 is powered by the ignition switch so according to your tests, 7 and 8 should have been included as having power with the ignition switch on. I assume the car runs so 7 must be powered because it connects to the fuel pump and 8 must be powered because it connects to the CDI. Both of these connections are on the line side of the fuse so if either fuse blew, you'd still have a fuel pump and CDI. Your tests make me think you were checking on the after fuse, load side terminal.

If you are not getting a reading on fuse terminals 7 and 8 with the ignition on, and your car runs, there has to be a problem with the fuses or the connections at the terminals, IMO.

[T77911S]

if you are having problems with only the rear and both sides, the only common point is the wireing at fuse 8. even the grounds are seperate, but stilll need to be cleaned.