car jump starting question

tabs

Active Member
i was always under the impression that you connect red and black leads to red and black terminals on the battery

i was told last night by an RAC geezer that you connect the red lead to the red terminal, but you DO NOT connect the black lead to the black terminal .. the black lead has to go on a non moving part of the car ....

is this correct ? .. if so, where ? .. engine block ? .. wing ? wheres best ? :confused:
 

BB3Lions

Distinguished Member
a. Connect (+) positive red cable to the (+) positive terminal on the dead battery.
b. Connect the other end of the (+) positive red cable to (+) positive terminal on the working car.
c. Connect (-) negative black cable to (-) negative terminal on the working car.
d. Connect the other end of the (-) negative cable to the (-) negative terminal on the dead battery.
 
the negative of the cable coming from the car thats running goes onto the engine block - or any part of the engine you can clamp the cables onto...the reasons for doing this are : 1 the terminals on a battery are quite close and could come off and touch so best to move further away...2 the engines resistance via the cables will stop the car from getting a 'jolt' so its safer to jump start the car this way.
 

clockworks

Well-known Member
Since the body and engine are connected to the battery negative anyway, it doesn't really matter where you connect the lead. As Baldybouncer said, connecting to the engine is probably safer, plus it'll work better if your old car has earthing problems.
 

Chadford

Distinguished Member
Had the AA out for the Mrs car a couple of years ago (faulty battery). I'm pretty sure the guy said that you shouldn't have the 'good' car running before connecting the leads to the 'dead' car. This is because the 'jolt' can take out the ECU in the 'dead car. He said that Mercs were highly susceptible to this and some of them have 3 ECUs which can, and do, fry. :eek: £££££££££

In the olden days before ECUs this was obviously never an issue.

Please correct me If I'm wrong and had misunderstood what the AA bloke was talking about.
 

Member 55145

Distinguished Member
always connect the leads before starting either car. then start the good car first and while its running start the flat car. (This is to stop you accidently draining the good car too much so it wont start! lol )

but yes, pos to pos, neg on good car to any metal body part on bad car (Pref not painted!)
 

MrSossidge

Distinguished Member
Years ago I jump started my old Fiesta Mk1 of my Moms diesel Sierra (I did say years ago!).

When taking the leads of my car I put them both into one hand whilst I went to get the other end off of her car which was still running.

The ends in my hand touched and the top blew off her battery showering acid and bits of plastic all over the place.

I ruined a shirt and had a very sore ear.

Now, I call the AA/RAC.
 

nheather

Distinguished Member
Also the reason why you connect the positive first is as a safety precaution.

The reasoning, is if you fumble a lead anywhere it falls into the chassis or engine is likely to be negative.

So if you have connected the negative first and then fumble the positive then BIG FLASH.

If you connecting the positive first and fumble, no problem because the negative isn't connected yet.

If you have connected the positive first and fumble the negative then the chances are it will come in contact with something that is negative anyway - again no problem.

Cheers,

Nigel
 
D

Deleted member 30535

Guest
Had the AA out for the Mrs car a couple of years ago (faulty battery). I'm pretty sure the guy said that you shouldn't have the 'good' car running before connecting the leads to the 'dead' car. This is because the 'jolt' can take out the ECU in the 'dead car. He said that Mercs were highly susceptible to this and some of them have 3 ECUs which can, and do, fry. :eek: £££££££££

In the olden days before ECUs this was obviously never an issue.

Please correct me If I'm wrong and had misunderstood what the AA bloke was talking about.

The "official" AA instructions for jump starting a car.....

4304535325_95f436426c_o.png
 

petrolheed

Active Member
Had the AA out for the Mrs car a couple of years ago (faulty battery). I'm pretty sure the guy said that you shouldn't have the 'good' car running before connecting the leads to the 'dead' car. This is because the 'jolt' can take out the ECU in the 'dead car. He said that Mercs were highly susceptible to this and some of them have 3 ECUs which can, and do, fry. :eek: £££££££££

In the olden days before ECUs this was obviously never an issue.

Please correct me If I'm wrong and had misunderstood what the AA bloke was talking about.
A friend had this happen on a slk, £four figure repair:(
jump start was done by the book but still blew the instrument cluster and SAM. overcomplicated poorly built MOD EDIT....dont circumvent the swear filter.:facepalm:. Still love them though :smashin:
 
Last edited:

John7

Well-known Member
The reason for not connecting the final (neg) connection to the battery is because batteries emit Hydrogen gas and a spark near th battery can cause it to explode.
 

steve69

Active Member
plus it can buckle the plates inside the drained battery which will total it.
 

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