Electrical Issue in main power cable of SpecE30- ideas?

[redrocket328]

Hey guys, Im really stumped right here so I thought I'd through it out for some opinions and Ideas. This is a SpecE30 racecar that is highly modified. There is a lot of electrical work that has been done but most of the stock wiring hasnt been touched.

Here's my setup:
Brand new OEM BMW battery is located in the trunk. I am running the stock 00 guage power wire from battery, through the cabin and into a 6 pole kill switch that is located under the hood. The wiring comes back out and goes into the stock + distributor block mounted on the firewall and stock from there.

Here's my issue:
When I insert the ignition key, insert the kill switch key, flip on all the power switches, and hit the start button, the starter will not turn and I hear a quick little click and all the lights in the cluster dim a bit and nothing happens. When I let off of the start button the lights come back to normal illumination.
For kicks I thought, ok, maybe the battery is dead so I hook up jumper cables to the front distributor block and ground to engine and car fires right up. So then to check, I hooked up the jumper cabels to the battery side of the power wires and the car didnt start. Same symptoms.
Then thought, ok, maybe the kill switch is bad. So i hook up a jumper wires to the output end of the kill switch and it started up and then hooked the jumper cables to the input side of the kill switch and it started up. So kill switch seems good.
In my mind, that would narrow the issue down to between the female end of the main power wire that connects to the battery terminal and the O-ring terminal connectors that connects to the kill switch. In short, the main power wire.
I am thinking that somehow where the wire attaches to either the O-ring connector or the battery terminal connector is corroded out and needs to be pulled off cleaned and put back in. I had a similar problem on my E39 540i so I might start there when I get back. The stock power wire where it connects to the terminal connector must have not had a clean connection so I had to pull the while wire out, remove the terminal connector, clean and reattach. Does any body have any other ideas of what might cause this issue or am I pretty much down to what might be wrong? Thanks.

btw, I left the car yesterday completely confused and while in the shower this morning I was thinking and made my conclusions.

[priapism]

Is the lead from the battery shorting out somewhere along the way to the motor? Stripped interior = lots of metal to ground out on.

[redrocket328]

I could certainly check to verify that there arent any shorts but I wouldnt think so. Those oem cables have a pretty good plastic insulation around them.
And everything works fine power wise unless I try to start the car. If there was a short, I believe there would be an issue at all times.
I would think that starting the car draws the most current, and when that much power is drawn, the connection cant withstand that kind of a current.

[jlevie]

I see two possibilities. One would be a high resistance in the cable from the kill switch to the battery and the other would be a high resistance in the ground cable from the battery to the frame.

[redrocket328]

I see two possibilities. One would be a high resistance in the cable from the kill switch to the battery and the other would be a high resistance in the ground cable from the battery to the frame.

What might cause this? the connections? Corrosion in the cable or connectors?

Solutions? Replace the entire cable? or replace the connections?

I am thinking that I am going to get a new O-ring connector and a universal battery terminal connector to throw in the ends up the cable without replacing the cable. Its always a possibility but im really doubting the actaully cable is bad. Or am I wrong?

[spdracrm3]

do you have a voltmeter ,if so load the system (ie a draw like all lights on)and voltage drop test the entire circuit (page 7 of every BMW ETM manual shows you how) downloadable here http://www.wedophones.com/BMWManualsLead.htm and it will tell you exactly where the problem is ,your right in thinking you have a corrosion/connection/resistance problem somewhere in the circuit so just need to know how to test for it and voltage drop test is it..... if your going to be racing and maintaining the car no time like the present to learn this diagnostic test as you will use it again and again

[AndrewBird]

Could be as simple as a bad ground at the battery. I would double check the connections at the battery before anything else.

[jlevie]

What might cause this? the connections? Corrosion in the cable or connectors?

Solutions? Replace the entire cable? or replace the connections?

I am thinking that I am going to get a new O-ring connector and a universal battery terminal connector to throw in the ends up the cable without replacing the cable. Its always a possibility but im really doubting the actaully cable is bad. Or am I wrong?

To connect the cable to the kill switch you had to have terminated the cable in a ring terminal. That connection needs to be a solder joint, not a crimp. Unless the cable has been damaged, the battery connector (if clean and tight) shouldn't be a problem. But there could be a poor connection on the ground cable from the battery.

I realize that placing the kill switch on the cowl is popular because it is the easiest solution. But that is a bad location. A good hit on the right front corner can result in a short and fire. Also it doesn't take much damage to render the kill switch inaccessible. The best place to mount the kill switch is where the harness bar meets the main hoop. An alternative that is just as good is to mount the switch on the inside of the right front down tube. In either case that places the switch inside the cage and in easy reach of emergency personnel. That also means that the hot side of the switch is located entirely within the cage area and thus protected from damage.

In a like manner, it is best to move the battery to the trunk floor between the shock towers. In it's normal location it is in the crush zone and is at risk in an incident.

[redrocket328]

do you have a voltmeter ,if so load the system (ie a draw like all lights on)and voltage drop test the entire circuit (page 7 of every BMW ETM manual shows you how) downloadable here http://www.wedophones.com/BMWManualsLead.htm and it will tell you exactly where the problem is ,your right in thinking you have a corrosion/connection/resistance problem somewhere in the circuit so just need to know how to test for it and voltage drop test is it..... if your going to be racing and maintaining the car no time like the present to learn this diagnostic test as you will use it again and again

Thanks. I do have a volt meter. Usually just use to to check simple voltage inputs but im sure i can figure that out. My question is, what exactly would that test tell me? Would it just confirm that I have a resistance issue?

[spdracrm3]

yes a voltage drop test will tell you exactly where there is above normal resistance in a circuit (ie bad connection,internally corroded wires). nice thing is you can go to every junction in the circuit and narrow it down to the exact location rather than guessing .

if you look a a diagram for example and a circuit has a connection at either end ie load (headlight) power source on other end (ie fuse ) and a switch in the middle you should not have over .3v drop in entire circuit (measuring between headlight and fuse ),no more than .1volt drop for every connection in a circuit is normal with circuit on(loaded) .so if in that circuit you had 4v on voltmeter you have a problem so you go between each junction till you find the one over .1v and theres your offending connection and you can now look closely at that part for problem

[StereoInstaller1]

Can you post a link to your kill switch? I have never seen a proper battery disconnect that was 6 pole.

[jlevie]

I think the OP means a kill switch with six connections (a three pole switch)

Any car with electronic fuel injection needs a 3 pole kill switch. That switch will have one pair of NO contacts for the main battery cable, one pair of NO contacts for DME power, and one pair of NC contacts for an alternator bleed to ground.

[StereoInstaller1]

Jim, is that SpecE30 rules? PRO3 uses an old school battery kill, just a 600A single pole mounted on the back of the car.

[jlevie]

Jim, is that SpecE30 rules? PRO3 uses an old school battery kill, just a 600A single pole mounted on the back of the car.

The multi-pole kill switch is to satisfy general competition rules. A kill switch must be able to stop the engine as well as isolate the battery.

A single pole kill switch that simply disconnects the battery isn't guaranteed to stop the engine. Even though the battery is disconnected, the alternator can (and usually will) keep the DME operating and thus run the engine. You need at least a two pole switch to stop the engine with one of the poles interrupting power to the ignition coil or DME.

The third NC pole is just for protection of the car's electronics. When you disconnect the battery on a running engine the alternator can spike. With no battery to absorb the spike there is the possibility of damage to the electronics. The NC contacts connect to a resistor going to ground to absorb that spike.

[redrocket328]

After spending time with the car today, it came out to be a bad ground cable to the engine. I put a jumper from the battery(+) to the distributor block and still didnt start. Put a jumper from the battery (-) to the engine block and fired right up. At that point the only thing it could be was the ground strap on the engine. Replaced with one I had laying around from a parts car I had a while back. Starts up and runs great.

Jlevie, thanks for clarifying, but yes you are correct. My brain was fried at work when I posted originally. And yes it is used to properly ground the alternator and isolate the battery when the switch is used. I have seen other people use a standard 2 pole switch and run the alternator wire into the switch and just have the one main power cable running back to the battery. I dont know why they would do that since it doesnt properly ground the alternator and can cause some serious issues when used.

Thanks for the help guys.