Hey all,

Recently I purchased an old X300 with a no start issue which I believed to be the Crank position sensor on the vehicle (it had two frayed wires) The car also had a marine battery installed which I believed to be insufficient for the needs of starting the car.

I changed the Crank position sensor for a brand new piece and connected the old marine battery which came with the car.. the lights came on and there was nothing but a click when I attempted to crank it.. OK, time to connect the brand new battery I bought.. in my excitement, I didn't realise that this brand new Diehard battery had the polarity at opposite ends from all of the five other batteries I own.. anyway as it turns out I had connected it wrongly.. only for a second.. there was a dramatic spark and I disconnected it straight away.

Now I have an issue.. whenever I connect the battery (correctly!) as soon as I attempt to attach the negative post, the lights come on but there is a lot of sparks and smoke.. almost as if the battery is being connected the wrong way around all over again.
I've checked for anything obvious such as cables which are bridging, fuses all seem to be fine and I've changed around the relays. I've studied the electrical diagrams which have been posted up in previous threads and I've looked for the 250 amp power fuse which is supposedly under the rear seat but the diagram in the pdf was rather unclear and I wasn't able to locate it.

In summary, I connected the battery leads incorrectly once and now the battery will spark dramatically when it's connected correctly.. I've tried multiple different batteries to no avail.. suggestions?

Thanks.

 

To access the power fuses, remove the rear seat bottom. On the right side of the car, you'll see a triangular piece of grey foam, remove that and the fuses are under it.

I bought a non running car for a very similar reason, the owner had connected the battery backwards. It fried the main ECU and the mass air flow meter, so I expect a few major electronic component replacements are in your future.

 

Try removing all your fuses and replace them one by one to try to determine which circuits are shorting. It may help. Good Luck!

 

Whilst reversing the polarity is never a great idea, if it was truly momentary, it would be very bad luck to have fried anything. Thinking laterally, could the problem you are now encountering be what took the car off the road originally, rather than one you have caused? 95Leapers suggestion is a good one in any event, and I would suggest keeping your mind open to problems other than just those that might have been caused by reversing the polarity. Good luck!

 

Sparks and smoke would suggest to me that this is not an issue with an individual fused circuit.

I would connect a multimeter (reading resistance) across the + and - battery leads (without the battery) - I assume there is continuity between the two. Then start disconnecting major parts of the system wiring - study the power distribution diagrams in the Electrical guides that can be downloaded from the stickies.

Here's a few suggestions for major power junctions to disconnect for testing

- 250A fuse under the rear seat
- Bulkhead power connectors (left and right)
- Starter Motor power lead
- Alternator power lead
- Fuse Box power connectors (5 of them)