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Why do I get a spark when I reconnect the ground to the chasis?

Absolutely - assuming these are small sparks and not something looking like an arc welder:biggrin:. You're completing an electrical circuit that has current flow. There's some minimal dc current drain, plus all the electronics have capacitors that draw a spike of current as they charge back up to 12 Vdc.
 
Absolutely - assuming these are small sparks and not something looking like an arc welder:biggrin:. You're completing an electrical circuit that has current flow. There's some minimal dc current drain, plus all the electronics have capacitors that draw a spike of current as they charge back up to 12 Vdc.

Ahh, thanks. As I fiddle with getting it alligned and screwed, it sparks "pretty bad." A bit "scary" imo.. just fine after the connection is slow.

Anything I can do to lessen it? A battery cut off switch I think is probably the best way to go..
 
A battery cutoff switch just moves the spark from the battery terminal to the switch contacts. However, the switch is one solid, quick connection versus a "bouncing" multiple connection attempt as you slide the cable's clamp onto the battery post. And it seems much less threatening when you are not holding the sparking terminal in your hand. But, there's no real electrical advantage to the switch; its a convenience item.

There's a spark whenever an electrical circuit is completed via mechanical contacts. That's why the contacts on switches, relays and similar devices eventually get pitted.

Note that if anything is on that draws extra current (beyond the computer and radio memory inputs in their "car is turned off" states) - say you have a door open and the courtesy lights are on - that will increase the intensity of the sparks.
 
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Did you solve your battery draining problem?

Joe,

I saw your response on about the 20th, then it disappeared, then came back again on the 25th. Some posting magic?

If he's having extra "off" current drain from add-on alarms, sound systems, etc, it of course will draw more current and a bigger spark. So far, no response from him to your question
 
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Joe,

I saw your response on about the 20th, then it disappeared, then came back again on the 25th. Some posting magic?

If he's having extra "off" current drain from add-on alarms, sound systems, etc, it of course will draw more current and a bigger spark. So far, no response from him to your question

No magic. I changed my mind and recind my offer to help.
 
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