Rebuilding my L20B

[datzenmike]

See if you can find a plug suitable to fit the harness. Then wire to the tach and just plug it in. This makes removal easier later for repairs or if sellig it or th truck and it doesn't hack the stock harness.

[ErickwithnoK]

See if you can find a plug suitable to fit the harness. Then wire to the tach and just plug it in. This makes removal easier later for repairs or if sellig it or th truck and it doesn't hack the stock harness.

 

Errr....too late 

 

[/url]">http://

 

I already committed a Datsun sin and chopped it.

 

I think my larger question is: If I run my black/white wires from the tach to the green/black wires in the harness will the tach work.

[datzenmike]

 

 

See that black wire with the loop? That has to be in line with the wire between the coil negativeterminal and the distributor. One end of the black to the coil and the other to the distributor. This early tach is an inductance type. Later style like your truck had a single wire to the coil. I've had one of these in my 620. I don't remember if the I had to reverse the two black wires or not if it didn't work..

[ErickwithnoK]

 

 

See that black wire with the loop? That has to be in line with the wire between the coil negativeterminal and the distributor. One end of the black to the coil and the other to the distributor. This early tach is an inductance type. Later style like your truck had a single wire to the coil. I've had one of these in my 620. I don't remember if the I had to reverse the two black wires or not if it didn't work..

 

That sounds like I shouldnt try to wire the coil/distributor wires into the harness, but run two through the firewall to the negative on the coil and one to the distributor. Will this tach even work if I switch from points to a matchbox dizzy?

[datzenmike]

YES. Sorry that is a much safer idea.

 

Yes it will work with either points or the EI. Mine was EI. All the tach 'sees' is the coil being turned on and off.

[hang_510]

By #2 you mean an r1 manifold? Yes please...

PM your number and I'll send pics of everything

[ErickwithnoK]

YES. Sorry that is a much safer idea.

 

Yes it will work with either points or the EI. Mine was EI. All the tach 'sees' is the coil being turned on and off.

 

Thanks a lot Mike! I'll give it a go, hopefully I'll see where/how to wire things once I get under the hood. At this point I'm not sure exactly where to put the wire on the dizzy or the coil. 

 

Might be back with pictures and questions again.

[datzenmike]

Look on the coil . The two terminals are clearly marked + and -. You want the - one.

 

Coil - >>>>>> black wire >>>>>  tach  >>>>> black wire >>>>> distributor.

 

You may need to reverse the wires if it doesn't read, I can't remember. You have a 50% chance of it being correct anyway.

[ErickwithnoK]

Look on the coil . The two terminals are clearly marked + and -. You want the - one.

 

Coil - >>>>>> black wire >>>>>  tach  >>>>> black wire >>>>> distributor.

 

You may need to reverse the wires if it doesn't read, I can't remember. You have a 50% chance of it being correct anyway.

 

I've got the wire to the coil on, but am wondering how to wire the distributor. There's only one wire on the distributor, and it's this one: 

 

[/url]">http://http://s1253.photobucket.com/user/erickwithnok/media/IMG_20170617_142123_zpssy3agglq.jpg.html'>

 

Do I just slap a ring terminal on my wire and put it under that screw? That seems janky...

[distributorguy]

Janky?  Its wiring.  Use a ring terminal or a blade-type crimp connector (so you don't have to completely disassemble it).  

[ErickwithnoK]

So I've tried it where I put my wire on the distributor and the negative on the coil.

 

The tach is functioning, but it seems like about half speed. What I would guess to be 6k rpm is showing as 3k on the tach.

[ErickwithnoK]

Janky? Its wiring. Use a ring terminal or a blade-type crimp connector (so you don't have to completely disassemble it).

I only say it's janky because it means I have to either disconnect the wire that is currently on the blade connector or have a ring terminal under a very small screw that probably wouldn't make good contact.

 

I disconnected the old wire and put my new connection on the blade.

 

My new connections from coil to distributor can replace the other wire completely, right?

[distributorguy]

Yes.  Disconnect and discard the old wire.  Its not uncommon to develop corrosion in that screw - enough to cause a bad connection to the points.  I think its just a generic M4.  You have a bad connection somewhere, or its not firing on 4 cylinders.  Got 2 plug wires crossed?  1-3-4-2 counter clockwise at the distributor.  1-2-3-4 front to back on the engine.  

 

Ohm out those new Belden wires.  If they're higher than 5000 Ohms each, get rid of them.  And make sure you have non-resistor spark plugs.  My guess is that you have about 15-18000 Ohms per cylinder with the plug and wire.  Bad.  1000 would be ideal.  

[ErickwithnoK]

Thanks for the help sir!

 

Plug wires are to the right cylinders, just double checked.

 

The wires are at 5k ohms each.

 

How do I know if I have resistor type plugs or not?

 

Also I'm (obviously) new to this stuff, I don't quite understand why resistance at the plugs/wires effects my tach reading. Mind explaining? Thanks again.

[distributorguy]

Its more about how the engine runs and trying to eliminate possible issues for a misfire.  If your distributor or HT ignition isn't right, you may get that errand tach reading.  

 

You can Ohm a plug from tip to tip (not the ground electrode).  Generally speaking, if there's an "R" in the plug number, its resistor.   That would make 10K Ohms resistance - a drivability issue for certain.  Your wires will barely pass muster even f you have non-resistor plugs.  

[ErickwithnoK]

Its more about how the engine runs and trying to eliminate possible issues for a misfire. If your distributor or HT ignition isn't right, you may get that errand tach reading.

 

You can Ohm a plug from tip to tip (not the ground electrode). Generally speaking, if there's an "R" in the plug number, its resistor. That would make 10K Ohms resistance - a drivability issue for certain. Your wires will barely pass muster even f you have non-resistor plugs.

Ok, thanks. So I need new wires, and I'll test the plugs/read them to look for an R in the name.

 

I have what I think is called a ballast resistor next to my coil. Could this also be adding resistance?

[ErickwithnoK]

I tried removing the old wire at negative on the coil, but the tach doesn't operate at all without it connected. It only works with my wire and the old wire connected.

 

On the distributor side only the new is connected.

[distributorguy]

The tach wire AND the distributor wire need to be attached to the - side of the coil.  

 

The  ballast resistor is on the low tension side of the coil.  

The plug wires and plugs are the high tension side of the coil.  

Two very different animals.  

[ErickwithnoK]

OK, will do. Thanks for the explanation.

 

So the distributor wire from the coil still needs to be attached to the distributor as well?

[ErickwithnoK]

Distributorguy, since you are the distributor guy, could you recommend a coil and a set of wires (and maybe plugs if I shouldn't just buy non resistor NGK's) to run with my new matchbox distributor? That's my next project, and I was told I can't run the stock coil with the matchbox. 

[distributorguy]

Just order up a factory replacement type coil for the '80 620.  Plug wires - I recently bought 3 sets from RockAuto and all of them were out of spec for resistance.  I ended up buying a set of universal V8 plug wires and making a set that fit right, and have the right resistance.  I prefer Moroso BlueMax 8mm wires.  If you can find Bosch, they use a similar wire, as do many of the Taylor sets.  

[ErickwithnoK]

I will look into that, and when I get my new stuff I'll post here whether or not it makes my tachometer accurate or improves the drivability of my truck.

 

Thanks for all the help

[hang_510]

 I ended up buying a set of universal V8 plug wires and making a set that fit right, and

 

...and you get 2 sets!

More colors available too, green makes 5 more HP!

 

No resistor needed for the matchbox! A new coil is cheap, you don't need 1,000,000 volts.

[banzai510(hainz)]

simple I don't run a tech. no worries.

if you do buy a good one

 

sometimes a tach will have a adjustment for 4 6 and 8 cyls. might be a switch or a solder junction to adjust.

[ErickwithnoK]

simple I don't run a tech. no worries.

if you do buy a good one

 

sometimes a tach will have a adjustment for 4 6 and 8 cyls. might be a switch or a solder junction to adjust.

It's a Datsun tach