Z3 Battery Cable Route

[IanA]

Hi All- just had an issue with a Z3 2.0 where it was running OK and then stopped with all electrics dead.
It appears that the battery cable that runs to the fuse box area has failed. The "main" battery connection to the jump start point is OK.
I got home by connecting a second battery - +ve to the cable terminal in place of the failed cable and -ve to a convenient body bolt.

My question is- what route does the cable take to get from the battery to the fuse box behind the glove box on a RHD car.
Thanks in advance.

 

[Althulas]

Hopefully the wiring diagrams resource may be of assistance https://zroadster.org/resources/2000-z3-z3m-electrical-troubleshooting-manual-for-great-britain.43/

 

[Althulas]

I don’t know if this video will be of relevance but it talks about the safety feature blowing has this happened to yours?

View: https://youtu.be/kXk4CqD8q2A

 

[t-tony]

Never known a cable to fail unless it had been damaged and shorted to earth blowing the protection (fuseable link).

Tony.

 

[IanA]

Thanks for the input. It did seem strange that it stopped dead with no warning and certainly no sign of short-circuiting. I suspected a fuse or relay but the cable takes a lot of power. I'll watch the vid and check out the fusible link idea- better than pulling up carpets or whatever.

 

[IanA]

After further investigation, my original question stands. The main (200A) fuse by the battery is OK.
For the cable in question, 12.5v from the battery turns into 3.8v at the 8 terminal busbar behind the glove box.
Connecting a second battery to earth and the busbar there brings the electrics to life and the car starts and runs OK.

 

[colb]

Must be some high resistance in that cable somewhere along its length, it runs from the battery under the car in plastic trunking alongside the brake pipes as far as I remember, need to check out the entire length for any damage and clean connections either end. I thought the earlier suggestion of that blowable connection in the boot was going to be your problem.

 

[IanA]

Thanks for the quick pointer, Colb. No problem with the connections- very clean and tight. The terminals are solidly crimped. It'll be up on ramps soon. Very strange that there are no other signs.
I now need a time domain reflectometer. TDR-ing it would show exactly where the problem is. An Android app for that perhaps? Just need a BT Open Reach van to venture into the close.

 

[colb]

Have you tried putting a jumper wire from battery post to the outer part of the cable that runs to the front of the car so it bypasses the pyro cut off to see if you then get 12volts at the front of the car doing that will prove that the pyro shut off has fired or gone bad. You could further explore it by pulling the cable out of the pyro housing as shown in the video in the earlier post. Really cant see there being anything going wrong with the cable run under the car.

 

[IanA]

The battery connection via the pyro delivers 12v to the jump terminal and the starter at the front of the car.
The cable via the green covered 200A fuse shows 12v at every terminal on the fuse block.
Going to the other end of that cable behind the glove box, it shows 3.8v.
Logic says something is wrong with the cable. Take it out of the circuit by connecting a battery in the footwell to the busbar and an earth- the car will start and run.

 

[t-tony]

Does this throw any light on the problem?

View: https://www.youtube.com/watch?v=c26Jq1O1m0M

View: https://www.youtube.com/watch?v=_yqXIhNNE9I



Tony.

 

[IanA]

First job tomorrow, remove the black cover from the BST module. I'll be surprised if it has blown because the car will still start using that cable. It's the cable via the 200A fuse (under the green cover) to the glovebox busbar that has the high resistance and the 12.5 to 3.8v drop.
One more thing, the car stopped whilst driving on a flat surface at about 5mph. No bump.

 

[colb]

OK the picture clears it up a bit, think we can rule out the pyro connection as you say the lack of voltage is on the secondary cable running through the green fused link which terminates at the fuse board under the dash where it only shows a low voltage. As I understand it that feed through the green fuse is there to keep certain things in an operational state should an accident happen that blows the main cable to isolate the ignition like centreal locking and hazard lights. I assume having passed through the green link it should show 12v and the same at the other end under the dash? Lets hope someone with more knowledge of this chips in, meanwhile best check out the cable run from last known good 12v along its length to see if you can spot any damage that would cause resistance to drop the voltage.
I suppose there could be a section of copper corrossion inside the cable run thats been festering away over the years gradually building up and causing high resistance, a bit like the loom of doom when the wires fatigue and break. Think thats a bit of a wild guess as the wire should have been well clipped in along its length so it wouldn't move like the boot loom but still a possibility worth checking.

 

[IanA]

Something that you couldn't know- there was some welding done for an MOT two years ago and the rather inept result is pictured. They didn't even remove the sill panel. Time for a wheel off/ inner wheel arch removal exercise. Not taking bets- I think this is where the problem is.

 

[t-tony]

It’s possible, but, that did not have to be welded to pass the MOT test as the outer sill is not structural and is only “bodywork”.
If they failed it for that they shouldn’t have done.

Tony.

 

[IanA]

It was long before my ownership but I questioned the previous owner about the MOT history and he said it had been attended to following the MOT failure.

 

[colb]

The cable run is a good way inboard of that welding on the outer sill cover but wonder what is under that, maybe inner sill was welded as well? Need to get under the car to inspect the cable run to see if there is any damage.

 

[IanA]

The wheels appear to be Type 5 but with an unusual hub cap.
Q. How to remove the hub cap please?

 

[t-tony]

Often with that type of cap there is a 3mm hole which you put through a strong wire type puller with an “L” shape bend on the end.

Tony.

ps. Is there any such tool in the tool kit?

 

[IanA]

I can't find any such holes, neither is there anything in the tool kit that looks appropriate!!!