Negative or positive grounded?

September 9, 2006 8:53 PM

How do I determine if my 1997 Toyota T100 truck is negative grounded or positive grounded?

I'm trying to hook up a battery charger to the truck, but I need to know if it is negative grounded or positive grounded. The manual makes it sound like most everything is negative grounded, but I just want to make sure.

posted by reishus to travel & transportation (8 answers total)

If you have an voltmeter, try checking each terminal relative to bare metal on the engine. Even if your battery needs charging, it's still going to have some sort of charge, so one of the two battery terminals will show no voltage relative to the engine and the other will show either plus a few volts or minus a few volts.
posted by Steven C. Den Beste at 8:56 PM on September 9, 2006

What he said, or just pop the hood and look at what the negative terminal is connected to. There are normally ground harnesses that connect to the chassis and engine block that route to the (-) terminal.

And I would say there is probably a one in a million chance that you have a positive ground vehicle. I thought they stopped making those in like 1934 but I really am no expert.
posted by Rhomboid at 9:17 PM on September 9, 2006

Rhomboid writes "I thought they stopped making those in like 1934 but I really am no expert."

Ford had postive grounded stuff into the 50s but your T100 is negative ground.
posted by Mitheral at 9:27 PM on September 9, 2006

Pretty sure Mitheral is right- but another easy way that doesn't involve the engine compartment is to use a voltage meter or one of those super-cheap 12v lamp probes.

Touch one side of the probe/voltmeter to the outside ring of your cigarette lighter with the key on to "ACC" or the engine running. Touch the other side to an exposed metal bit of the vehicle. If your truck is negative grounded, the light will stay off and the voltmeter will read 0.

If it's positive grounded, the lamp will light or the VM will show a large potential difference (12.5-14v).
posted by fake at 9:31 PM on September 9, 2006

The last vehicles to have positive ground electrical systems were British cars in the fifties and sixties (MGs and such). Here is a Toyota wiring repair manual telling you that Toyota's are negatively grounded.
posted by Derive the Hamiltonian of... at 9:33 PM on September 9, 2006

damnit, stray apostraphe... *Toyotas*
posted by Derive the Hamiltonian of... at 9:34 PM on September 9, 2006

Look at the battery - it should be obvious to look at which wire is grounded to the engine block.

Although, it seems people have told you already
posted by jimmy0x52 at 9:35 PM on September 9, 2006

If all you're doing is charging the battery, it doesn't actually matter which side of it is connected to the vehicle ground. Just connect the red charger clip to the battery + terminal, connect the black charger clip to the battery - terminal, and switch on the charger.

Switch it off again before undoing the clips; hydrogen gas + spark + battery acid = bad.
posted by flabdablet at 6:45 AM on September 10, 2006