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Tips

How to use timing light with positive ground?

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PeterB

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Do you still hook the red up to the positive and black up to the negative with a positive ground car? I am just nervous and don't want to damage anything.
 
With the unit I own, Actron CP7528 Advance, the instructions say for 12v positive ground systems - connect black to negative, red to engine ground.
 
If the timing light has metal on the outer casing, don't touch that to the car while it is hooked up.
 
I am looking at a equus 5568 digital that does dwell, tack, and voltage. The literature says for negative ground cars. Have anyone used a digital on a positive ground car before? Just want to be sure before I drop the cash. Thanks
 
You have to be careful with electronic items as most are polarity sensitive and won't work unless they have a switch or other way to "reverse" them. What you might do, if the manufacturer has a website or other contact information is call them and ask first.

My personal, cheap, timing gun works fine both ways by swapping the leads from what negative ground uses.
 
If you connect red to the positive battery post, whether positive or negative ground, works fine. Been using my dwell, tach, timing light tools for decades, even replacement units, on positive ground with no issues.
My dwell/tach is battery + and distributor, just connect red lead to distributor (which through the points becomes battery +) and it works fine.
 
Another option is to use another battery to power the light. Just set it on the garage floor near your AH and you are good to go.
 
Just wondering if you ever did get your Equus 5568 and used on your +ve ground AH ??
I am contemplating the same thing.
Called their tech support and 2 people did not understand the concept of just reversing the power leads they kept referring to an external battery with an internal negative ground ..!!
I do accept that if the electromics is connected to a metal case there could be a problem or that there might be a reference problem with the pick up.
Any other ideas..??
 
For years, I have simply used an external power source for the red(+) and black(-) clip leads for my timing light. I have used spare batteries, a battery charger, a 12VDC power supply, and most recently a Power Pak for jumping cars. I have done this on my +ground BJ7 and just about every other vehicle where the vehicle battery is not in the engine compartment. Just clip the timing light trigger to #1 wire and do it!!! While I have not allowed the metal case of the timing light to touch metal on the BJ7, I cannot see how it would matter as long as the vehicle and the external power source are not electrically connected. The timing light does not care where it gets its power.
 
Since the 100M battery is behind the seat, I connect the riming light ground to the engine (typically the heater valve) and the power to the terminal on the starter or starter switch. I did this when it was positive ground and after changing to negative, just switched the connections. Worked very well. My timing strobe is probably 35 years old (space age design!)
 
John Kuzman said:
For years, I have simply used an external power source for the red(+) and black(-) clip leads for my timing light. I have used spare batteries, a battery charger, a 12VDC power supply, and most recently a Power Pak for jumping cars. I have done this on my +ground BJ7 and just about every other vehicle where the vehicle battery is not in the engine compartment. Just clip the timing light trigger to #1 wire and do it!!! While I have not allowed the metal case of the timing light to touch metal on the BJ7, I cannot see how it would matter as long as the vehicle and the external power source are not electrically connected. The timing light does not care where it gets its power.
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It won't (matter), since the car chassis and the external power supply are different circuits. But, if the timing light has a metal case it is likely grounded internally, so if your car is positive ground and you power the light from the car battery and ground (red lead to ground) and you touch the case to the chassis you will create, in effect, a spot weld.
 
If you have a multimeter measure the resistance between the light's positive and negative leads and the light's case to see if the case is isolated. Use the lowest Ohms scale.
 
Use any external battery - perfect. I didn't think of that. The light just needs some 12v power. It doesn't care if the power comes from the lawn mower battery, right?
 
Right. Even a half dead lawn mower battery will work. If the light flashes when you hook it up and pull the trigger that's enough. They draw little current.
 
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