Using Snap On Analog oscilloscope for 6 volt positive cars

[busaf44]

I am Using a Sun TUT-915-R scope on a 6 volt positive ground system.  The Sun manual states unit is  for  12 volt negative ground systems. 

 

On the pick up probe assembly there are a red and black wire for primary ignition testing . I presume one should reverse the red/black leads so black wire from scope goes on + side of coil (which should go to distributor)and red to a good ground on car so an accurate dwell can be taken

 

On the trigger harness, there is also a red and black wire that the manual shows go directly to the battery.

I presume these wires serve for non ignition electrical measure and the timing light power. Is it correct to presume to connect red to ( +) and black to (-).

 

[TerryB]

I would think the battery connections you mention will need to be connected to a 12v neg ground source like a free standing 12v automobile battery to work.  For example, a 12v neg ground powered timing light can be used on a 6v car provided the light electronics gets its power from a 12v source.

Edited May 13 by TerryB (see edit history)

[Bloo]

I'm not sure that will work at all. I have not used that particular unit, but I have used a lot of ignition scopes. Assuming clips that "clip around" the coil wire and #1 plug wire, you *should* be able to get a secondary pattern, using a separate 12V battery to power the scope, and not connecting any other wires to the car.

 

EDIT: I just looked that up. This is a roll-around? Does it plug into the wall? If so you don't need a battery to get the secondary pattern.

 

Primary pattern though? Dwell? No. Don't do it. The most likely scenario in my opinion is that it wont work and it will damage the scope. This also goes for any dwell meters that have 3 wires or more, or are digital.

 

Ideally you need a 6v positive ground capable dwell meter if you want to set the points with a dwell meter. Many of them just don't say. The dwell meters most likely to work would have only 2 wires (so they can be hooked up either way). If there is a "set" knob that you set to a particular line on the meter scale, there is a good chance it can compensate for lower voltage. Not every dwell meter that can work on 6v uses a "set" knob, but a lot of them do.

 

Primary patterns are overrated anyway. I am not saying they are useless, they do have merit, but are usually not necessary to find whatever problem you are chasing.

 

Edited May 14 by Bloo (see edit history)

[Glen Andrews]

I have hooked up a 12V dwell meter to a 6V (neg ground) system, and adjusted the dwell and rpm settings. I ran into a problem later, I think the 12 volts messed with the condenser. Not long after doing this I had my vehicle sitting in the driveway running for a few minutes and then it stopped running. A check showed no spark at the plugs, so it's either the coil or condenser. After about 15 minutes I hooked up another 6v coil and it started up so I figured the original coil was cooked, left the extra coil hooked up and a few days later pulled my truck into the driveway, let it run a few minutes, then again it stopped running, so I quickly hooked up the original coil and the truck didn't start, then decided to change the condenser and it's been running good. I figure that first condenser got hot from the 12V, cooled and worked until it go hot again.