Weird DPO wires heating up really hot

[RickB]

My 'missing / cutting out' problem came back, so once again I started looking all over and after shutting off the car the other day I happened to put my hand on the wiring 'harness' coming out of the firewall on the drivers side.
It was <span style="font-weight: bold">HOT</span>.
I cut away the blue tape to reveal my white wire from the coil to the cockpit was the one getting really hot.
It was spliced into two other white wires going 'who knows where'.
One of these was a white wire that just headed out towards the front of the car. I know of nothing that direction that should be in that circuit so I cut it and started the car again, the wiring no longer gets hot.

What in the world was the DPO thinking? Why connect up wires to that circuit - I can't think of anything up in the engine compartment that should be on that circuit except the coil.

My cutting out problem was still there this morning, though it seemed about 75% less. I still have a problem, just not sure where. Have to find out where that other white wire is connected.

Never underestimate the powers of the DPO!!

 

[Deleted member 8987]

Relay for auxilliary cooling fan?
If it's gotten that hot, chack your voltage at the power side of the coil while running.
I don't think that car is a "resistor" fed coil, so the chances are pretty high you have a high resistance point in the splices or elsewhere dropping voltage to the coil.
If non-resistor coil, power side of coil should read battery voltage.
If you can't see much difference, check from positive side of battery (if negatively earthed) to power side of coil while running....which will give you the exact amount of drop.

 

[RickB]

Relay for auxilliary cooling fan?

Might have been at one time, but that's not how I wired it.

If you can't see much difference, check from positive side of battery (if negatively earthed) to power side of coil while running....which will give you the exact amount of drop.

I'll check that tonight. Might be that other spliced in wire also was used to activate a relay, I'll follow it and find out.

 

[Morris]

Hey Rick,

The 1500 was originally wired with a "resistor" wire that splices into that coil feed and runs to nothing in the front of the car. The 1500 coil in factory trim was an externally "ballasted" coil. The resistor wire gets hot by design. On my car, that wire is a very light pink (almost white) if I remember correctly... and I may not.

If removing what may have been the resistor wire affected your sputter problem... I would have a long hard look at your coil. If you were running an internally ballasted coil on that resistor wire, you may have fried it.

 

[Deleted member 8987]

If that's a resistor wire (still), and there are two taps off it, one of which overloaded the resistor wire until it was hot, I wonder where the other wire goes? Still need to know the voltage at the coil, running.
Don't recall a 79, but most 12V systems with a wire resistor give about 8-9 volts, running.
Could be an internally resisted replacement coil on a wiring loom resistor, giving far less output than it should.
This the one you had to jury-rig a replcement ignition switch into?

 

[RickB]

Yes its that one.
Datsun 1500 motor. For "some" reason the ignition wiring was over heating.

Bought a new coil for it recently, so it is the one for the engine not the car.
I have no idea what the DPO did to adapt the electrical system but clearly it's not perfect.
I had to do home maintenance after work rather than car maintenance.

 

[Deleted member 8987]

Okay, coil for engine not car can be an issue.
You need to find out if the Dat Soon coil requires an external resistor or not (possibly NAPA can tell you). If the coil requires no external resistor, you will need to run another "hot" lead down the harness from the "ign" post on the switch to the coil, connect at both ends after disconnecting (and taping) the old wire.

 

[RickB]

That actually sounds like a very good idea, I'm a fan of the new wire when the old is questionable.

I can find out about the coil needing / not needing a resistor today.

 

[Deleted member 8987]

Keep me posted. Today is not a good day to run up past the Falls, but mayhaps tomorrow.
Dave

 

[RickB]

Tomorrow I'll be at Bill's house (BillM) pulling the drive train again. We need to diagnose and fix a slipping clutch.
Maybe I'll stumble across whatever is causing the misfire while we are at it.

 

[RickB]

The resistor was not used so cutting it loose was correct.
Now I just need to locate the cause of that misfire and get a good working clutch in the car.

And do some body work
And get it painted
And make sure all my brakes are good
And put in new valve seals
And... And... And... And... And... And... And... And...



Drive to Wisconsin and back!!

 

[Deleted member 8987]

Okay, if no resistor on the Dat Soon coil, run a new non-resistor hot wire from ignition to coil.
Then, find out where that other spliced in wire went.

 

[RickB]

Okay, if no resistor on the Dat Soon coil, run a new non-resistor hot wire from ignition to coil.
Then, find out where that other spliced in wire went.

Now that's a good plan! I'll do it that way.
Thanks!

 

[Deleted member 8987]

I sent BillM a PM, maybe if he approves, I can swing by tomorrow.
I have a couple of pieces of test equipment, if it's running, to check spark intensity at the plugs and dwell, that kind of stuff.
Dave

 

[RickB]

Thanks Dave, we're going to start the removal process today after work then finish the job tomorrow. Hopefully this way we can get done before it gets late.

 

[Deleted member 8987]

I can come by in the morning, or later.

 

[RickB]

Engine will be out for several days to a week.