Will a VOM show a lower value with a ballast resistor when checking it?

Cranky

Henchman #27
Staff member
FBBO Gold Member
Local time
3:35 PM
Joined
Dec 4, 2009
Messages
26,920
Reaction score
27,221
Location
Down southeast Taxas
I'm showing full battery current when hooking one up......
 

69L48Z27

Well-Known Member
Local time
4:35 PM
Joined
Nov 19, 2015
Messages
3,608
Reaction score
3,810
Location
York, Pa
Not sure what your asking but if you check voltage, you should have battery voltage on one side and a low (resisted) voltage on the other. 12VDC vs 7VDC. I’m not sure what the ohm value should be.
 

Cranky

Henchman #27
Staff member
FBBO Gold Member
Local time
3:35 PM
Joined
Dec 4, 2009
Messages
26,920
Reaction score
27,221
Location
Down southeast Taxas
Thought a ballast resistor would show resistance when checking it by itself.....at least with voltage.....
 

69L48Z27

Well-Known Member
Local time
4:35 PM
Joined
Nov 19, 2015
Messages
3,608
Reaction score
3,810
Location
York, Pa
You would check it both ways.

With nothing hooked up check ohms. Closer to zero means no resistance for voltage drop.

With terminals connected, check voltage drop.
 

RJRENTON

FBBO Gold Member
FBBO Gold Member
Local time
3:35 PM
Joined
Jul 1, 2015
Messages
2,785
Reaction score
2,673
Location
South Shores area of Decatur, Illinois
Ballast resistance values are tested by disconnecting one or both of the wires connected to the resistor, setting the V-O-M (analog device like a Simpson 260 or Tripplett 630) to the R x 1 setting, shorting the rest lesds together, zero the instrument to show zero (0) ohms (usually full scale), unless it's an digital auto ranging instrument, then connect the rest leads to the resistor then read the resistance in ohms directly. When measuring resistance, no external voltage is applied to the device being tested.
3 1/2 or 4 1/2 digits digital auto ranging devices are extremely accurate a relatively inexpensive...like Harbor Freight's offering at less than $ 10.00.
BOB RENTON
 

sloinker

Well-Known Member
Local time
2:35 PM
Joined
Jun 6, 2020
Messages
270
Reaction score
247
Location
Wyoming
I have never had a ballast resistor short, thus applying the full 12 volts to the coil at all times. I have had them open, start and die or not start at all. You actually need a pretty good meter to read tenths of ohms. Checking for voltage drop is easy, check on both sides of the resistor(s) to chassis ground under all evolutions. Key off, key on, starting, running.
 

sloinker

Well-Known Member
Local time
2:35 PM
Joined
Jun 6, 2020
Messages
270
Reaction score
247
Location
Wyoming
That's been my experience, they are either good or blown open. I have actually seen carbon resistors lower in value in some cases of abuse but never a wire wound like a ballast in a car.
 
Top