Dictys

Hi, I'm trying to sort out a battery drain once the A/C button is pressed.

My cooling fans where aftermarket, but I have replaced them with stock units., the new fans worked fine but still the engine ran a little hot.

There was a external relay connecting the A/C switch to the A/C head unit, this has been returned to stock configuration.

The A/C works, however when pressed there is a large battery drain.

The two cooling fans fuses on the CE panel had burnt connections and where replaced by two external 30 amp fuses, but with the same drain.

I have now checked the battery compartment and see the mess below, are these two extra relays (black and grey) meant to be there? or should I remove the relays and put back to stock.

Does anyone kindly have a picture of stock layout looks like?

Leon Speed

Pictures are not working, but there should be no relays in the battery area.

Dictys

Weird, the pictures are showing both on my ipad and laptop.

It seems there are two relay with fuse holders connected to what would be the seven smaller red cables. Both hold 30 amp fuses.

Ok if i strip them out, and connect the red cables back to the battery directly, what the possible consequences? Either a drain is fixed or something more drastic occurs. Mmmm

I has already removed most of the po previous wiring mods, i'll return this area to what i believe is stock, no relays.

WallyP

If I understand what you are saying, changing how the wire is connected is not likely to fix a drain on the other end.

Dictys

Wally, the drain is somewhere in the circuit regarding the ac and the fans. I have removed an extra relay between the ac on off switch and ac head unit which was doing god knows what. Now i find these extra relays which the previous owner has put in and they are connected to the fan power cables plus some others. If i return everthing to stock, then at least you guys are giving me help based on known wiring rather than some po's hack job. If these relays were broken/corroded or plain wired incorrectly would they cause a drain. Can anyone else see the pictures?

WallyP

Possibly. Or, the relays may have been added by the PO to try to cure an existing drain.

Some general comments...
Electrical power will always take the easiest path to earth.
All of the electrical power must be used up in some way - that is, the power will go to earth thru a resistance. That resistance will determine how much power flows. For example, if you took one of the red wires attached to the battery positive and touched the other end to a good earth, this would create what the electrical engineers call a "crowbar short". (The term refers to what would happen if a worker's crowbar fell across the main power lines coming into a building - a major short circuit.) The very small resistance of the wire would allow several hundred amps to flow, almost instantly melting the wire. If you put a high resistance in the wire, say an instrument light bulb, the resistance would only allow a very small current to flow. The wire would be unaffected, and it would take days to drain the battery.

Your drain has to be somewhere between these extremes. There is not enough current flow to melt the wires, but enough to put a noticeable drain on the battery.

As you saw from your fan connections, current flow thru resistance creates heat. If you have a poor connection (high resistance) in a circuit, heat will be generated at the high resistance. This is not a short circuit. This will not create any additional battery drain, and is a totally separate problem.

To have a battery drain, something must be connected to the battery all the time that should not be connected with the ignition off.

The electrical power must be used in some way. Either something is working that should be off (fan, amp, light, alarm, etc.), or there must be some resistance that limits the current flow enough to keep the wires from melting.

It is important that you understand the difference between poor connections, a short circuit, and something connected that shouldn't be.

First things to check:
- Do the interior lights work exactly as designed?
- Is there any aftermarket audio gear installed?
- Is there an aftermarket alarm installed?
- Are there any lights on that should not be? (Glove box, engine compartment, back edges of the doors, etc.)
- Do you remove the key while the car is parked?

I hope that this helps!

Dictys

Thanks wally,

I think i have explained myself incorrectly, there is no drain whilst the car is stationary, only with engine running and ac button pressed. So more a voltage drop, so alternator can't recharge the battery enough. The voltage gauge drop from 13ish down to less than 12 and if i stop after a 30minute drive there is not enough to start the engine. If the ac is left off the battery is fine and alternator charges the battery fine. The problem being is that atpresent the outside temp is 110f+ so ac is pretty essential.

I'll remove the relay ans sort the interior lights and see where we are then, thank you for your help so far.

To answer your questions.

- Do the interior lights work exactly as designed?no, but i have all new lights,switches etc coming.
- Is there any aftermarket audio gear installed?no, there was but all removed including any wiring
- Is there an aftermarket alarm installed?no.
- Are there any lights on that should not be? (Glove box, engine compartment, back edges of the doors, etc.)no.
- Do you remove the key while the car is parked?yes

WallyP

The A/C and the two fans on high speed represent a large current draw, so your problem is likely to be a failure for the alternator to provide sufficient current to run the A/C and charge the battery at the same time.

The first thing to check is the tightness of the alternator belt. It should be tight! The timing belt (cam drive belt) should be 5.0 on the Porsche tension gauge - the alternator belt should be 9.0!

Dictys

Checked the alternator belt all good, but noticed the ducting had failed, so will replace this asap.

Also, I stripped out the two relays that had been added by the POin the rear battery compartment and now have the correct wires connected back to the postive battery post.

It seems these extra relay where designed so when the engine was started it would engaged the fuel pump, these relays had all the additional power cables running through them, various grounds and a connection out the battery box to to the positive connection on the fuel pump.

I have found the red/green wires to the pump which should be connected taped up. I also have the additional in tank pump. I'll check for voltage here and then rewire it back to the fuel pump as it should be. Once back to stock, I'll see if the pump engages and the engines fires. I'm geeting to grip with these wiring diagrams at last.

If all these red wires in the battery compartment where passing through these two little relays then this may be the cause of all sorts of electrical problems.

Once the engine is started I'll see if my drain is still there, but then I would have also done the interior lights.

fraggle

Sounds like you've got a lot of previous owner "fixes" to undo. You're on the right path - get everything back to stock and it will be a lot easier to debug with forum help.

Leon Speed

Right, "fixes". Sounds like a bypass for whatever problem there was. Good thing to get it back to stock first and go from there.

Mrmerlin

if you have an internal tank pump it may also be failed and the relays were added to make the pump work without fixing the original issue remove the internal pump and fit a screen,
tape up the internal pump wires