Disconnecting car battery

Fundamentally, no. But there may be practical reasons.

eg - if I jump start 2 negative chassis cars, I will connect the positive lead first. The other way around, I might drop one end of the live +ve onto the body of the other car and cause a short (= bit of a bang).

Basically, if the +ve is disconnected, the *only* way a reconnect can happen is if the +ve terminal is connected to the +ve lead.

If the -ve is disconnected, an inadvertent reconnection could happen if

In terms of jump leads, ISTR you connect +ve to +ve first, so you're not waving a +ve jump lead around when both cars are at the same earth potential.

You commonly disconnect the ground terminal as when working on the car near the battery, there is less chance of shorting things.

Just did some attempted checks to the ruddy airbag warning system wiring on

Your method is safer.

I have seen what can happen when the other end of the spanner used to disconnect the positive touches metal on the car whilst negative is still connected.

Mike

The safe way is to disconnect -ve first and reconnect it last. Then, if you're using something metallic to tighten the connection it doesn't matter if it touches the bodywork while you're doing it.

As long as there is no circuit, I do not see that it matters except your radio will never work again once the battery is off a car for more than a minute or so, in my experience. Brian

I always disconnect -ve first, for the simple reason that if you knock the spanner against the bodywork whilst you're undoing +ve, and -ve is still connected, you're going to get a big fat spark.

Can't think of many reasons to do anything else.

Why? That sounds like complete nonsense to me. Have you never changed a car battery?

The radios that I've come across have a code that has to be re entered after disconnection to hopefully stop them being used if stolen. They always work ok after the code is entered.

Sounds like the *only* sensible way to do it (assuming negative earth).

Tim

Many newer ones don't even have a code - they're so cheap these days that nobody nicks 'em.

And they appear to have proporietary fixings. I have no idea how our Citroen unit could be fitted into another model of Citroen, let alone another make of car.

Because plenty require a PIN if they have been disconnected, basically theft protection.

Fraid not.

Yep, and got that result, the radio didn't work anymore.

No big deal if you have the PIN, can be a problem if you don't.

About two thirds of postings to uk.rec.car.maintenance are requests for radio codes. OEM head units are, it seems, dead easy to figure the PIN for.

I took care to write down the radio code for one of my cars. When I happened to remove the radio, I discovered it was on a label stuck to it.

:-(

Chris

Having just got a new car this thread reminded me I haven't got the radio code. Then I thought hang on were is the radio? 7" touch screen, does satnav, radio, phone, etc. There is a panel with a few buttons and manual on off and volume and another panel near that with a slot for CD's/DVD's. ie the radio is fully integrated into the vehicle. There is no easy to get at, self contained, unit to nick.