RallyDogRacing

Hey all - I'm troubled by not being able to find a massive current draw when the car is not running. Well the draw is there while the car is running, but it's most obvious when the car sits overnight resulting in a completely dead battery. No click, no nothing. Flat.

I've got a measured draw of 11-17amps depending on the measuring device. The draw happens down one of the two large black cables that go to the + terminal on the battery. I know one of these goes to the starter direct, and the other according to the diagram goes to the fuse-block. The one with the draw is the "right hand" cable when viewed from the front of the car where they disappear into the bulkhead below the gas tank.

I have tried to isolate the fault to the fuse-block, but after pulling all fuses and relays the draw is still there. By my Fluke DMM, the draw is a steady 11.9amps with a battery producing 12.2volts. As troubleshooting efforts have progressed this far the initial changes have been a change of the battery and a replacement of the alternator. I'm figuring that was wasted money.

Tomorrow morning (Sat) I will be disconnecting the starter leads to see if the drain is related to it. Outside of that and inspecting the underside of the fuse block, I'm wondering if anyone can confirm which cable (left or right at the bulkhead) is the one to the starter and which one to the fuse block.. It sure would help.

Also if anyone has experienced the same draw characteristics I would love some advice. The car is a '90 C4 USA spec.

Rob in Chicago.

garrett376

Use your digital meter set to ohms with some really long leads, and put one lead at the wire in question in the trunk, then one lead on the positive cable at the starter - if you are on the same wire, it will change the reading to zero. That will tell you which wire is which.

I am surprised you can't find the source by unplugging the fuses and the relays.

Colin 90 C2

I'm guessing a stuck starter. That is a pretty high current draw. You should just be able to follow the wire by feeling the heat.

Toddimus

Either the starter is stuck somehow like Colin said above, or maybe your aftermarket stereo amplifier is stuck on?

That's a ***tload of of power!! 12V x 10A = 120 Watts!!!!

Are you sure your headlights arent't on?? I mean geez!, something has to be really hot to be drawing that much power.
Think of putting your hand in front of your headlight when it's on (50Watts), or a household 100Watt lightbulb. You should be able to find what's drawing the power by using your sense of touch.

Just my nerdy way of looking at the problem.

I found a ~5Watt draw in my climate control unit and I thought that was hard to find. Yours should be easy to find.

Seriously, if it really is a 10A draw, feel around for heat after a night in the garage, and you'll find your problem.

darth

I think the only component connectted directly to the battery without a fuse besides the starter is the alternator and since you replaced it (assuming it's OK) you can rule it out and the possibility of a shorted diode. Maybe look at the regulator since it is inline with the alternator or the alarm since it has an internal fuse?

Bill
90C2

RallyDogRacing

Thanks guys. The heat manifests itself at the negative post & lead from the battery. The battery itself if left connected overnight get's mighty hot. I agree the started seems a serious suspect, and I will mess with it after fully inspecting the solid-state chips on the underside of the fuse-block as it's mentioned as a rare cause of similar drain issues.

This has certainly been a fun issue - NOT.

Oh and, yes I can confirm that all accessories are off, there is no aftermarket stereo amps or anything. If indeed it is the starter - it's impossible to differentiate it's heat from the engine heat after I've driven it to my friend's shop.

springer3

There is no way 20 amps will heat the negative post and cable. You have a bad (high-resistance) connection. Fix that and I'll bet the current draw by the real problem will increase, possibly enough to make it obvious what the problem is. Good luck.

Indycam

Bad insulation on a cable ?

darth

I'm not aware of any solid state components under the fuse block. Along with the fuses did you pull the relays that are in the fuse box? If a relay is stuck "on", for example the one for the fuel pump, that would draw significant current. If all the fuses and relays are removed from the fuse box there are only 3 things still connects - starter, alternator and the alarm. The starter has the solenoid (another name for a heavy duty relay) between it and the battery - the solenoid can be either "on" or "off" and if it is "on" it's connecting the battery to the starter and that takes a lot more than 10 amps. Sinc you say you drive the car I would assume the starter/solenoid is OK. Was any work done on the car before this problem surfaced?

Bill
90C2

ltc

There is a very quick and easy way to troubleshoot problems like this.
Try and buy/rent/borrow a DC (magnetic) field probe/senor; preferrably one that can plug into your DMM.
The probe will measure the (DC) magnetic field produced by any wire carrying a current. You simply have to 'sniff' around with the probe near any/all wires. The closer you get to the wire carrying the current, the larger the output signal will become. NO need to unplug or disconnect anything.

No, I didn't stay at a Holiday Inn Express last night, I'm just a geek (electrical engineer)

dougn

yeah something is way fishy....the battery post and terminal should not get hot. it happend to me once due to a bad connection. how did you measure the current?

RallyDogRacing

I measured by using my Fluke DMM set to DC-Amp readings then connected it between the positive post on the battery, and then the positive batter cable. The DMM should be then reporting the current flow through the cable.

I completely disassembled gthe electrical and a majority of the car. I believed at one point that I had tracked the problem down significantly to be sourced in the fuse block. Specifically on connector G at pins 15 & 25. G15 had 9.8amps, G25 has 7.3amps indicated on the DMM. So many bewildering hours later poring over the fuse block diagrams and the other electrical diagrams and I was stumped.

So frustrated I decided to put everything back together to be able to drive it to a shop and have them take care of it. The short-version is I think something has changed because I no longer have the hot-battery-post issue. We're 6hrs later and drove it 35miles and still the problem seems to no longer be present. Tomorrow morning shall be the final proof if there's still enough juice to start. But knock-wood, I think in the end it just wanted me to spend 8 back-pain filled hours taking all the panels and interior out while tracing cables.

Oh if anyone wants to know the main battery cable routing on the C4 is as follows.
Battery to trunk bulkhead below the gas tank
Exits the trunk area and routes external over the differential
Enters the main cabin immediately adjacent to the where the steering rack does
Crosses over the transmission tunnel, and then splits.
One trunk returns to head up to the main harness that goes into the fuse block at connectors: G12, G15 and G25.
The other trunk runs allong the right-side tunnel
It follows the curve of the right-rear footwell exiting the mainbody there.
It comes out then follows a path over to the starter.

garrett376

Here's a supplement to your description:

Larry Herman

I would say that it sounds like one wire was shorted to the chassis. Maybe a wire got worn through and it is making enough of a connection not to blow anything, but to cause that current drain. I would carefully re-inspect the couple of conductors that stay energized even when the car is switched off. Otherwise your problem may return.

darth

any updates?