Hate to ask a dumb one....

560sl. Both battery cables are black, battery posts are not labeled + or -. Which is Pos, the one with the single cable or the one with one cable and the smaller qround cable attached. Siingle cable must be + but I thought I'd check just in case.

Thanks.

Take a closer look at the battery. Everyone I've ever seen has the terminal labeled ... even though the markings may be difficult to see.

__________________
Fred Hoelzle

but I would have to take it out of the battery box to see, just thought someone would know off the top of their head. Trying to avoid getting my starched white shirt dirty.

thanks.

JB

If, as you say, a wire leads directly from one terminal to a ground point, you can then be reasonably certain that it is, in fact, the negative terminal.

__________________
1989 300 SEL that mostly works, but needs TLC

The larger diameter post is the positive. Look at every car battery and you'll notice the posts are two sizes. Also look at any zip cord in your house.You know the extension cord your lamp is plugged into. One side of the cord is smooth, and the other side is rough to the touch. The smooth side is positive and should correspond with the black wire in the wall for safety.

__________________
Auto Zentral Ltd.

Just to nitpic this, but 'black' is not 'positive' - it is 'line' or 'hot' when referring to AC house wiring. Polarity of the line, of course, shifts both ways from zero volts at 60 Hz.

Steve

__________________
'91 MB 190E 2.3
'08 RAV4 Ltd 3.5
'83 Lazy Daze m'home 5.7

Another quick test: Touch one end of a 12v test lamp to chassis, and then the other end to either post. The positive, red or + terminal is the one that makes the lamp glow when the other end is 'grounded.'

This will work for all cars with 'negative ground' wiring. It is very rare for cars to have positive ground.

If you look closely at the cables at the posts, there are tiny little + and - on the cable.

Thanks.

JB

Steve you are technically right about AC, but I will technically let you hold onto the black wire and ground yourself while I hold onto the white wire and ground myself. The white wire is the grounded side while the green wire is the grounding side. Now the whole picture changes when you are working on a high voltage line in the air, because you are at a whole different potential from earth ground.

__________________
Auto Zentral Ltd.

..pretty much limited to pre-80's-era British cars...especially Jaguar.

__________________
2009 ML350 (106K) - Family vehicle
2001 CLK430 Cabriolet (80K) - Wife's car
2005 BMW 645CI (138K) - My daily driver
2016 Mustang (32K) - Daughter's car

Pretty much correct. That was called conventional theory. We are now using electron theory where electrons flow from negative to positive, but then again holes flow from positive to negative. We always say that the positive terminal is hot, but electron flow is how we measure current. One amp is 6.28x 10 to 18th electrons or one coulomb, and they come from the negative terminal.

__________________
Auto Zentral Ltd.

My 1969 MG has negative ground and a '76 Jag that I owned for 10 years had negative ground. I do know that mid sixties MG's had positive ground.

__________________
Paul 1987 300 SDL; 2000 ML; '69 MGB; '68 VW Fastback