84 5spd, the voltage at the pod and cigarette lighter drops to around 11volt with everything on. Is this ok. While I was down there I found that as I poked around the fuse block with a meter the more different voltages there were.

The question?

Is the voltage supposed to be consistant in the fuse pane using a multimeter connected to any point on the fuse block and ground? I have readings from 13.0v to 11.1 volts.

 

I have the same year and model as you and have been doing ALOT of voltage testing of late. I have had my DMM connected to the following places (all in pursuit of strange voltage surges and drop-offs).

1. Direct to battery posts
2. Between the exciter circuit (try pin H8 on the panel) and ground. This should read about 1.8V when you turn the key to the ignition point. Failure of this circuit to excite will cause your alternator voltage producttion to lag until your rev up to 3000 rpm.
3. Between an electrical feed point (larger red wires in between N and O plugs on board) and ground.

For the most part, you should get a steady 14.3V with all of these with the engine running. If you have your system under load (defroster, A/C, lights) then you will drop off a bit. But if you're getting 11.1 volts, then you should check to make sure that

a. your battery is okay
b. your alternator is okay
c. you've cleaned all of the ground points in the car

Running under 12.0 volts will not replenish the battery.

Peace,
Tim

 

I did some measureing yesterday and at the battery and at the post under the hood I was gettting 14 volts with the engine running no matter how much I turn on. So I know the battery is charging and won't leave me on the side of the road.
Now on the fuse panel my voltages are all over the place. However a few of the large red wires have good voltage. I need to get my hands on wiring diagram but I think I am also chasing bad grounds and/or connections.

 

There are several ground wires that terminate at the same location above the fuse/relay panel. I would start by checking/cleaning all of these indivdual ground wires to make sure they have continuity and a clean connection to the chassis.

 

One thing I am going to try. I have a cigartte light cord with no ends. I am going to hook up a meter to this and ground the negative and see if anything gets better.

Earlier in the year I had an intermittent fuel pump relay problem and am wondering if this low voltage would cause the relay to drop out. I know the relay needs a signal to pick up again so it would not reset by itself. This only happend when it was real cold outside.
Another theory I have is that the cold causes things to shrink and maybe cause a bad ground situation but things tighten up when it warms up again.

 

Measuring "any point on the fuse block and ground...." should they all be at 12v

... err no stop expecting crazy things...

Think about what you are doing... and be clear about exactly what you are asking - I'm not being a jerk - you can't get good answers without good questions..

Now at the top of the panel there are some big red wires - this is where power comes in - it is fed from the red wires on the jump post in the engine bay. That is in turn fed from the alternator which then connects to the starter and back to the battery.

Disconnect the battery and thoroughly clean those jump post connections first and reassemble.

You should get the same reading on those red wires to ground as you do at the battery.

All the fuses are connected to power supplies with inputs at the top and outputs feeding circuits at the bottom. Not all the fuses are direct connects to the battery but some are - mostly the ones in the middle of the panel. Some are fed only with the accessories or ignition on, some are fed by relays/switches and are only powered with equipment on.

Its too complicated to cover here which is which - varies by year and equipment.

If your battery voltage is really 11v without many accessories turned on - you likely have a battery problem - take it to be tested. If you only get 11v with lots of accessories turned on - it may be normal.

If you get between 13.2 & 14.2 v when the car is running at 1000 rpm then your alternator is generating fine.

As long as you get 12.7v or more at idle your alternator is also working fine.

You should test for voltage equivalency with the engine running - that is the normal condition - the battery should ideally be used only for starting the car.

Most fuses that are actually powered should be within ~0.5v of the system voltage (alternator generated voltage). Bear in mind that switching loads on may change the system voltage...

If you are really seeing bigger differences than this you may have some connection resistance issues.. any signs the fuse panel has been wet? - are the fuse terminals & connectors clean and shiny or dull & oxidized?

Alan

 

Not to be arguemetentative, but I have to disagree with Alan a little. I too am in the process of doing this on my '81. I have a presistent voltage drop at the instrument cluster (measured with a DVM) and went through the standard ground and terminal cleaning ritual with very little success.

One anomoly that has me a little puzzled is behind the fuse carrier, there are 2 or 3 large red cables that terminate onto a major buss / 2 busses that feed the fuses. I was getting a 1/2 volt difference on the left bank of fuses versus the right. Disconnecting the large red wire that goes to the left most connector, raises all the voltages to the same potential. As soon as that wire is plugged in, you can here relays click in and the voltage immediatl drops 1-1/2 volts on the left and 1 volt on the right.

All these measurements were taken with engine off and a 10 amp charger hooked up to the battery. My point is, behind the fuse panel I too am seeing a significant voltage drop and variation that I can't explain.

 

It seems this is what you are seeing... no?

A 10A charger is not the way to test it - your car's accessories need much more than 10A to operate - run the car - test with real world conditions - use 2 meters because everything you change will affect the system voltage level. The only thing relevant here is the differences. If the voltage is actually too low under load - that is a seperate issue.

Alan

 

The next thing I am going to try is find the circuit with the lowest voltage and trace it back to its source on the fuse block. Rather than just clean everything and hope it works.

The reason I asked about consistant voltage throughout the panel is that I wasn't sure if there were some circuits with resistors/diodes that operate at a different voltage. This is my first foreign car and expect thing to be different than what I am used to.

 

There are no seperate resistors or diodes that matter (those that exist are inside relays and not measurable). However Porsche does not always place fuses where you might expect and aften has relays come first. Mostly voltage levels on fuse inputs should be a system voltage (+- 0.5v) or floating depending on source & switching - since they are connected to equipment through the fuse in practice - floating lines may achieve some other voltage due to that... (so pull the fuse...)

Alan

 

I have used a jumper cable hooked up to the bat ground post as a reference to check for bad grounds. For example you could check the 11v point using the jumper cable as a reference... If you get 11v then the ground is OK and power is the problem. Good luck --Roy--

 

I finally got to go through some of my manuals on CD and printed the pertinent stuff so hopefully I can poke around tonight.

 

I'm sorry but I don't understand what you mean... This is a good way to validate you actually have 11v on a particular node - it really does nothing to validate a ground connection - for that you actually have to test the voltage on the (supposed) ground connection (and ensure it is under load while doing it).

This whole topic is best taken to specifics rather than generalities. What circuits seem to be misbehaving - evaluate exactly whats going on at specific circuit nodes and decide if it makes sense or points to a particular failure. These issues can be debugged.

I was probing around randomly and found a node at 11v is almost meaningless without knowing what exactly it was and what other conditions apply to that circuit...

Alan