Ohmmeter-reading question

P

Patrick Morris

Member
This is sort of a bonehead question. I always have trouble getting my head around how to read an ohmmeter.... Since I mostly use mine for checking basic connectivity rather than measuring resistance.

When the meter is set at "20k" ohms, and the display is showing 6.24, how many ohms is this? 6,240?
 
Hi patrick, I am not real sure what meter you have but the 20k setting should represent a 0 to 20,000 ohm range. So your reading is 6.24 ohms. An anolog meter(one with a needle) will make you use a different scale on the face or make you calculate the answer as you did in your post, but since you said 6.24 I assume it is digital.
Ron
 
Yep, it's a digital multimeter. Craftsman. I'm pretty sure you have to move the decimal point over as you go 'up' in scale. For instance, when I put the leads across a 33-ohm resistor with the meter set at its lowest, "200 ohm", the gauge reads 32.9. So that reads true for this ohm range. But if I set the meter to the next setting up, "2k ohm", and measure the resistor, the gauge reads .032. So you have to do a little math when measuring this stuff.

To get right to the point, I'm measuring the resistance of my plug wires. The 6.24 reading is for the coil wire, which is about a foot long. So I'm wondering, do my wires have a resistance of 6000 ohms/ft? And I know this isn't bad, since a lot of oem wires have more, but are there benefits to going lower resistance, like <1000 ohms/ft. On a Scout engine? (1978, prestolite/pertronix dizzy, msd6, Holley 2300, etc.)
 
All this "plug cable resistance" shit and specs is for oldskool carbon/graphite impregnated secondary cable. The generic "spec" for that shit is all over the place,but a general rule is 2,000 ohms per foot of length including terminations.

Modern "spiral wound" cable (fuck the "od" of the insulation, that is marketing meaningless shit) is not considered to be resistance-type cable used for rfi suppression and while ya can certainly check continuity/resistance, the values are much lower than oldskool resistance cable. Any modern silicone jacket cabling outwrap is rated at far more than 1,000kv per mil of "insulating" properties unless penetrated mechanically.

Modern spiral-wound cabling uses a "choke" effect for attenuation of rfi, far more effective than resistance cable....and far more durable, the stuff can be lifetime if cared for. One brand is the same as any other in that regard.

Regarding "specs" such as for this stuff...there is "then" and there is "now". If you are using then stuff, use the then specs. If you are going modern, than it's a whole new game.

Hell...folks that deal in model a Ford stuff still use copper strip for spark plug "cables"...works just as well today as it did in 1928. But then, the spark plugs for those rigs were rebuildable also, ya only replaced the center electrode when it eroded away.

The use of modern spiral-wound cable negates the potential for the "crossfire" (inductive crossfiring) effect which is the reason that IH and many other oems routed spark plug cables away from their mates on cylinders that were adjacent in the firing order. The choke effect of spiral wound cabling negates the need to do that...oldskool secondary cabling enhances that effect.

Things change...in the case of modern secondary cable, it's all for the better. Again...we're dealing with 35+ year old vehicles that were not even close to "cutting edge" of technology when new. But all the stuff we play with around here ignition-wise enhances performance/drivability/reliability because technology has marched on.
 
Interesting, but I'm still puzzled. I think what you're saying is... Who gives a crap about measured resistance, so my question doesn't deserve an answer?

Also...

"the values are much lower than oldskool resistance cable."

Which values? Do you mean the ohm readings will be numerically lower? Or that the conductance is lower? And what would be considered old-school values (numbers)? And what are the new-school values? No comprende. You speak in generalities too sweeping and broad to be helpful, in this case anyway.

These are new 7mm "premium" cables from napa, if it matters. Nothing fancy in the least. I don't care about the dia. Either... In fact I'd prefer narrower. The old/existing cables (borg-warner, CA. 1996) are being replaced only because I've ripped the ends off of the #5 and #7 wires so many times. I'm sick of pulling the wires from the plugs only to find that either just the terminal, or both the boot and the terminal, are still on the plug. And of course I'm left with a shredded end on these wires, so these two wires get shorter every time I "check the plugs".

I still wouldn't mind knowing how to read the meter. The instructions that came with spend about two or three sentences explaining how to use the ohm meter feature.
 
Yes when your meter is set to the 20k range a reading of 6.24 would represent 6,240 ohms. On the 2k range a .624 reading would be 624 ohms.
 
greg r said:
Mike: what plug wire set do you use?
Click to expand...

Whatever 8mm spiral-wound cable I can find that is most affordable, normally these days it's accel ss universal sets.

I normally buy the cable only in bulk (by the foot locally) and keep all types of terminations on hand to make up whatever I need.

The Ford performance "trade name" universal cable sets are also an excellent value.

The actual cable material nowadays comes from only a couplea root manufacturers...most of the current crop of automotive secondary cable (both oem and aftermarket) comes from here:

prestolite wire llc

With silicone terminal boots it's imperative to use boot grease and invest in a boot removal tool to prevent damaging terminations when doing plug/cable service.
 
Thanks Mike. Yes, I too use the grease and removal tool. Not play'in with this stuff full time in a chang'in market, it's good to get direction once in awhile.
 
I've always greased mine. And I bought a tool for grabbing the boot. But I haven't found a tool yet that works. I have a yellow plastic plug-boot tool, but it's too flexy to grab the boot effectively. In my situation it would have to be a) just as compact, and b) very rigid. My problem is that there's no room to work with for those two cylinders, between the smog-pump tubing and the brake mc and booster, there's no room to work with and apply force. I can't even touch the boots with my fingers, let see them or clamp a tool to them. Been trying to do so for years and I just end up with shredded hands from the edges of the smog tubes.

I've always had a related problem when installing the wires again. The boots are too short and I can't get my hands in there and apply the necessary force to make them snap onto the plugs. Kind of like pushing wet spaghetti.

The only thing that works for me is longer boots. Preferably the kind with the flared ends--best for both pulling and pushing on. I added those to my old wires and will likely swap them over, or something similar, to whatever I use for the new ones.

This is a high-zoot sample of the kind I bought through napa:

boot sample image

I wish I could find a set of wires that already uses this style of boot. I actually looked at msd's site this morning, at the bulk wiring, etc. I would not mind making up my own set. Msd is the only site where I was these components pieced out. I would likely need a better crimper than the cheesy one I currently have though.

Mike: how many feet do you recon it takes to make a set for a 345 (plus 1' coil wire)?
 
michael mayben said:
whatever 8mm spiral-wound cable I can find that is most affordable, normally these days it's accel ss universal sets.

I normally buy the cable only in bulk (by the foot locally) and keep all types of terminations on hand to make up whatever I need.

The Ford performance "trade name" universal cable sets are also an excellent value.

The actual cable material nowadays comes from only a couplea root manufacturers...most of the current crop of automotive secondary cable (both oem and aftermarket) comes from here:

prestolite wire llc

With silicone terminal boots it's imperative to use boot grease and invest in a boot removal tool to prevent damaging terminations when doing plug/cable service.
Click to expand...

Why mess with the universal stuff when you can get a direct fit set from an original supplier to IH, prestolite, so you know the fit is correct. The easy to find ones have the carquest name on the box and wires but if you look at the fine print on the back of the box you will see that it states that they are manufactured for carquest by prestolite. Cq #35-8315, presto #108002 for the Holley (male cap ends) equipped rigs and cq #35-8316, presto #108003, (female cap ends) for the prestolite rigs.
 
eric vanburen said:
why mess with the universal stuff when you can get a direct fit set from an original supplier to IH, prestolite, so you know the fit is correct. The easy to find ones have the carquest name on the box and wires but if you look at the fine print on the back of the box you will see that it states that they are manufactured for carquest by prestolite. Cq #35-8315, presto #108002 for the Holley (male cap ends) equipped rigs and cq #35-8316, presto #108003, (female cap ends) for the prestolite rigs.
Click to expand...

Because I prefer to do things the difficult way eric.

Here we go again.
 
I was going to say, it might be... Fun? To make them yourself.

I went by the local carquest after work. Good people working there. They ordered a set of those prestolite wires, to be in by 8am tomorrow morning. I'll check them out too I guess. They don't come with the boots I kinda need though.
 
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