Sparks when connecting battery

[jsl5150]

So after about two years I thought my Z would be ready to roll today. I charged the battery overnight, made sure it took a charge and put it back in the car. I connected the positive cable first, but when I connected the negative cable sparks started flying. I heard a low kind of humming (or frying) coming from the starter/solenoid. I disconnected the negative cable right away. So what do i do know? Ive never had sparks like that before and haven't done anything to the electrical. What could it be? I know JACK about electrical, any help would be appreciated.

[Zed Head]

Are you sure that you're not putting them on backwards? Datsun did not use the red = positive, black = negative that domestic cars use. I don't know what happens if you do, but it's worth confirming.

Or, could your key be in the On position when you were connecting the battery? Maybe you heard the fan motor?

Make sure that the key is off and that you don't have any positive wires shorting to ground. If you have an ohmmeter, you can check the positive cable to see if it has a path to ground BEFORE you reconnect the battery. Put one lead on the negative terminal and one on the positive, without the battery in. If you don't have infinite resistance then you have a short or something is on.

Or if you have a test light, hook up one battery terminal, then test from the other unconnected cable to the remaining post. If it lights up, then you have a short or something is on. This will let you find your problem without frying anything.

Hopefully you didn't melt anything,but you should probably check your fusible links and look for scorch marks.

[Bruce Palmer]

Also hopefully you didn't charge the battery backwards which can happen with deader'n a hammer batteries....

[FastWoman]

You can certainly test your entire system for electrical conductivity with a multimeter, but you neeed to disconnect your radio first -- both the main fuse and the memory fuse. The reason is that it may have discharged capacitors and will otherwise have a baseline current draw that might mess up your measurements.

But yes, check the polarity of the battery first. You can actually reverse charge them if not careful (although that's mostly a deep cycle battery issue). I bought a camper once that was running a reverse-charged battery. (RV color codes are weird, so I guess the PO got confused.)