Very basic electrical problem.

rmcdonnell · 05:24 PM

Hi Folks,

My '89 944 2.7 sometimes goes electrically dead. During the starting process, sometimes all power dies (including systems always attached to power, like door locks, parking lights etc) so I clearly have an intermittent connection between the battery +ve and circuit 30, which supplies pretty much everything. Because these systems are all around the car, and I'm certain the battery to earth connection is good, the problem has to be the +12V feed.

Can someone explain in gory detail exactly how the +12V connects to the fuse box which is in the engine compartment on this model.

I'm assuming the +12V from the battery, (in the boot) gets to the front of the car as one nice thick wire, because it's mainly got to get to the starter, but I don't know if it goes on to all the other systems after it gets to the starter, or the feed splits at some sort of bulkhed connector to be distributed to other fused systems, with a thick wire continuing from there to the starter.

Can someone give me some clues about where this bulkhead connector can be found, or if there is a known connection that can cause this sort of intermittent trouble.

The car has never died while running, though I can't see why it hasn't; perhaps vibration makes the connection ok, but it still has to deliver all the current requirements of the car. I have no idea how this works, but at least once it's started, it keeps going

cheers
Russell

Lawrence Coppari · 03-31-2007, 03:24 AM

If I understand your problem, the interior lights and whatever else go out when you turn the key to operate the starter in order to start the engine. If this is the case, I would clean and reinstall the battery terminals. Sometimes you cannot see the corrosion. The large draw of the starter motor hogs all the current if there is a bad connection.

1988_944 · 03-31-2007, 04:40 AM

Yes check the battery connections. Also the ground from the battery to the chasiss.
Does the starter start to crank and then power goes dead?
When it goes dead while trying to start , does the power come back when you let off the key?
Does the starter seem slugglish while cranking?
If so then there is a bad connection on the main 12v system.

rmcdonnell · 09:00 AM

Hi,

Thanks for the replies, and you are correct that it has all the symptoms of a poor battery connection or earth. But it is not the battery terminals or earth connections anywhere.

So, I know I have an intermittent +12V at the fuse box on circuit 30 which should be permanently wired on, but I don't know exactly where it is likely to be intermittent, apart from the battery where I'm sure it isn't!

So, I'm just trying to find out from someone who knows, where and how the connection to circuit 30 is made in the fuse box, and where and how the +12V cable gets from the back end of the car to the front, and where it splits to the starter and alternator and fuse box etc.

If anyone has a circuit, or diagram of the main power loom components for a 1989 944 2.7, or just knows how the power is connected to the fuse box on the later model 944's with engine bay mounted fuse box I'd be grateful for any info.

The schematics for earlier cars show extra leads from the +12V battery connections, which don't exist on this model.
So I'm expecting there to be a bulkhead connection, or these to split after getting to the starter motor.

Basically, do I lie on my back under the motor, or do I lie on my back with my head under the passenger footwell?

cheers
Russell

1988_944 · 03-31-2007, 04:44 PM

Ok , To make sure i follow. The car starts but circuit 30 goes dead? Or does it drop out while the engine is cranking?

Razorback1980 · Razorback1980's Garage

Not sure about the S2, but the NA picks up the power from the starter terminal. Check for app 14V on the main starter terminal...if less, then the connector at that end may be corroded and need replaced. I usually buy new ones and I make sure they are soldered connectors to keep the air out. I'll look around and see if I can find a wiring schematic for your year and model and post it if I can.

rmcdonnell · 06:53 AM

Thanks Tom,

Ok, sounds like I should be looking for corrosion on the starter terminals, or another problem with the link to the fuse box emanating from there. So on my back under the engine it is..!

Neal, yes the circuit drops out while cranking, but the starter is not slow or short of volts until it stops dead. I think Tom has pinpointed the correct area to investigate.

Cheers
Russell