av been jump startin wagons 4 a good few years and always gone just put them postitive to postive, negative to negative on the batterys in any order and never had a problem with either truck after doing this !
i’ve 'jumped plenty battery to battery, it only takes one though, tried to jump a foden gritter and as the negative lead went on the spark ignited the gasses from the battery and blew the top off, i was lucky and only lost a pair of overalls to the acid. i couldn’t have put the negative lead on the chassis though as fodens were wired isolated return (no chassis earth) as are many tankers.
the problem with ecu damage is due to a sudden increase in voltage when the leads are connected, i know ERF reccomended switching on lights and heater blower to reduce this.
the idea that the ECU doesn’t recieve voltage until the ignition is switched on is wrong as the ECU will have an ignition feed, an accesory feed and also a permanent live, it’s the latter that’s monitoring the battery voltage without anything being switched on that ‘notices’ the sudden voltage increase.
mark h:
av been jump startin wagons 4 a good few years and always gone just put them postitive to postive, negative to negative on the batterys in any order and never had a problem with either truck after doing this !
Yes, it’s true and in practice I never do any of that battery isolator stuff either, just whack the jump leads on and get it going… this “cook the ecu” thing seems to have become a bit of an urban legend, a bit like CDs in the windscreen were in the 1990s.
Any make, any model, red to red, black to black. Simples! 
ashbyspannerman:
the idea that the ECU doesn’t recieve voltage until the ignition is switched on is wrong as the ECU will have an ignition feed, an accesory feed and also a permanent live, it’s the latter that’s monitoring the battery voltage without anything being switched on that ‘notices’ the sudden voltage increase.
So explain why turning on the battery isolator, which completely disconnects the battery, doesn’t fry the ECU. Explain why swapping out batteries doesn’t fry the ECU. Both events provide an almost instantaneous rapid rise in voltage.
Conor:
ashbyspannerman:
the idea that the ECU doesn’t recieve voltage until the ignition is switched on is wrong as the ECU will have an ignition feed, an accesory feed and also a permanent live, it’s the latter that’s monitoring the battery voltage without anything being switched on that ‘notices’ the sudden voltage increase.So explain why turning on the battery isolator, which completely disconnects the battery, doesn’t fry the ECU. Explain why swapping out batteries doesn’t fry the ECU. Both events provide an almost instantaneous rapid rise in voltage.
both of those scenarios involve the voltage stepping from zero to 24 volts, the problem with early erfs was that when the voltage to the ecu was reduced and then stepped up suddenly they gave up the ghost, i’ve heard of later ECU’s having this same problem but not come across any myself, i think the main reason drivers are warned not to try jumping is the usual h&s bull in case some muppet can’t tell his positive from his negative!
Conor:
Why for my benefit? Related technical qualifications:
O level Physics with Electronics
O level Control Technology
BTEC HND in Electronics Engineering
CGLI 383 Pt2 Repair & Servicing of Road Vehicles.Related experience:
Bench engineer Euromax Electronics dealing with circuits far more delicate than anything now that took a damned sight bigger spike than hooking up jump leads
Auto Electrician and Vehicle Mechanic in REME
Auto Electrician at Halfrauds
Mechanic at Arncliffe Nissan, HullWhy do you think your comment is of any benefit to me?
A bright spark !!! 
Harry Monk:
mark h:
av been jump startin wagons 4 a good few years and always gone just put them postitive to postive, negative to negative on the batterys in any order and never had a problem with either truck after doing this !Yes, it’s true and in practice I never do any of that battery isolator stuff either, just whack the jump leads on and get it going… this “cook the ecu” thing seems to have become a bit of an urban legend, a bit like CDs in the windscreen were in the 1990s.
Any make, any model, red to red, black to black. Simples!
the only time i have had a battery blow up was when we was tryin to jump start the 12v container lifter pulled wagon next to it live an earth fitted to the lifter, earth fitted to the scania, and then a quick touch on the positive (24v) while turning the lifter over then bang the battery blew on the wagon, 
schrodingers cat:
Harry Monk:
Cruise Control:
strangely if the battery not strong enough (or “dead”) to krank the starter motor it will power the lights, even on full beamthey require less voltage i am assuming
Less current yes, but current is not the same as voltage. The starter motor is by far the greatest drain on the battery set. Just think how much power is required to spin a 12 litre diesel engine over at high speed using an electric motor…
To differentiate between current and voltage, just think of two rivers, a little one and a big one.
Water flows down both rivers at two feet per second, that’s voltage.
Far more water passes down the big river, that’s current.
Nice one Harry saved me from going into the big pipes little pipes plumbing analogy.
Why is it when anyone tries to explain about electricity they use water as an anology? 
Ne’er shall the twain mix 
I too have been jump starting vehicles for many years without problem, just after they stopped fitting starting handles as standard equipment. I also remember when Arncliffes were a dodgy second hand car dealer in Hull.
However since the age of technology and on board computers I have used the methods described in the first post and not blown an ECU or a battery up yet, however I do know 2 people and Willie Mac is a third who have lost an eye due to exploding batteries either through blocked vents, frost or misconnections.
Even with my spell at Ontime Automotive where several of the trucks were fitted with a built in slave system to start immobilised cars. Several of the main customers, Aston Martin, Ferrari, Maserati and Audi VW prohibited the use of them and we had to call out the manufacturers to jump start them.
The nearest I got to injuring myself was with a pair of 6 volt batteries brought in to recharge. I neglected to remove the glass balls and they went through an asbestos roof 
do drivers not carry any kit nowadays?
i thought most would carry jump leads.
surely no one would call out a mechanic/fitter because of a flat battery?
it’ll be blown bulbs and susies next.
limeyphil:
do drivers not carry any kit nowadays?
i thought most would carry jump leads.
surely no one would call out a mechanic/fitter because of a flat battery?
it’ll be blown bulbs and susies next.
You only need one jump lead and a wheel brace, if you haven’t got a wheel brace, just run into the other truck with the donor vehicle to create a good earth
Wheel Nut:
limeyphil:
do drivers not carry any kit nowadays?
i thought most would carry jump leads.
surely no one would call out a mechanic/fitter because of a flat battery?
it’ll be blown bulbs and susies next.You only need one jump lead and a wheel brace, if you haven’t got a wheel brace, just run into the other truck with the donor vehicle to create a good earth
i could imagine someone welding the two together. errrrrrm boss, i think we need a hack saw.
Wheel Nut:
I also remember when Arncliffes were a dodgy second hand car dealer in Hull.
You tell him Mal. Stick that amongst yer “O” levels conor.
Dunno about frying ECU’s, but I fried the boss’s brain today; Scania R500 with flat as ■■■■ batteries, I tried cranking it over, not even a flicker of a light on the dash so I connects the big battery charger we have. That did the trick, I could see the interior lights come on that some fool must,ve left on 
. What didn’t do the trick was the loud clunk as the doors locked themselves! My how we all laughed for two hours on the hard shoulder as we struggled to gat the quarterlight firstly out and then back in again.
the maoster:
Dunno about frying ECU’s, but I fried the boss’s brain today; Scania R500 with flat as ■■■■ batteries, I tried cranking it over, not even a flicker of a light on the dash so I connects the big battery charger we have. That did the trick, I could see the interior lights come on that some fool must,ve left on
how did it manage to get flat batterys on the hard shoulder?
Do try and keep up old bean . as I’ve posted before I’m doing the free recovery bit you see on motorway roadworks.
the maoster:
Do try and keep up old bean
arr right gotchaa !! i was driving a scania day cab ex/tesco and had it ticking over in the dock, shuts drivers door an locked myself out both doors locked had to get the fitter to rir the whole door handle off as they rnt fitted with side quarter window on n/s or sunroof haha
Well TBH Mark I was gonna boot up tinternet to see if there were any “cheats” about to get into the truck but luckily it had a quarterlight and it seemed so straightforward to remove.
It was, but a nightmare to get back in, half a bottle of washing up liquid, lots of blood and elastoplasts did it though.
Won’t fall for that one again mate.
the maoster:
Well TBH Mark I was gonna boot up tinternet to see if there were any “cheats” about to get into the truck but luckily it had a quarterlight and it seemed so straightforward to remove.
It was, but a nightmare to get back in, half a bottle of washing up liquid, lots of blood and elastoplasts did it though.
Won’t fall for that one again mate.
yerr mate we have took the quarter light out once before and was a struggle to get back it back in, easiest way to do it is get a pry-bar in the side of the door handle at the edge of the door an rip it off, unclip it and use the bar’s to unlock the door, u do wreck the handle like but if u drill through it u can fit 6mm bolts it if you dont want to buy a new handle
I’m with Quinny on this one. Had flat battery at Barnet some time ago. Another artic was overnighting at the same place. Connected his units tail lift Anderson connection to mine and started with no bother.
Since then I have also used the same method to start one of our trucks in our yard at home after it had been sat around for a week.
Comments about the ECU being ‘fried’ are slightly over exaggerated. However, if you connect batteries with the ignition on, there is the potential to damage the ECU by introducing a voltage “spike” whcih can damage small electrical components such as transistors.
When you connect the batteries, you should do it with the ignition / master switched off. When you switch on the master switch, the “dead” vehicle is drawing current from the live truck to which it is physically attached (by means of jump leads) acting as it would do normally from its own battery.
With regards to vehicles having separate connections for jump leads, one would assume that this is purely because the +ve terminal on the battery (similar like on a modern car) is connected to the radio and suchlike, which will require reprogramming if you remove both terminal connections when attempting to jump the vehicles.
I’ve jumped started plenty of vehicles in this manner without any problems.
TM