Introduction & Electrical Mess - 1984 720 King Cab 4x4

[dustinsandwich]

Okay, I soldered the Green wire to its corresponding cut wire. It seems to be the horn, thanks to EDM620. Horn still doesn't work, but I'm thinking that these unconnected wires might have something to do with that:

That was the random red wire, which goes behind the steering wheel. I think I may have to take the wheel off and see if they jumped the connector or something.

 

Headlights are now doing this:

Lights on (dim in both brights bulbs, lit on drivers)

Brights on

 

I also found another cut ground, I think:

Not sure where it's pair is. 

[dustinsandwich]

Correction, all bulbs are dim except driver's side main light.

[EDM620]

Search for a 720 factory service manual - years ago I managed to find one online somewhere (maybe here on Ratsun?) that will help you sort through the wiring.

 

There are peculiarities dealing with the OEM wiring for sure. While I cannot determine the issue with the 2 black relays you have, I have determined that the OEM Blue relay / headlight circuit doesn't follow normal logic IMHO. For example: a standard 5 pin relay is configured as below:

 

The weird thing I have recently discovered is that the 720 uses a fuse for the Left and Right headlights separately, yet the relay combines both and has 2 grounds. Having difficulty wrapping my head around that.

[EDM620]

35 minutes ago, dustinsandwich said:

Not sure where it's pair is.

Those are the flashers. One is for the hazards, the other is the signals.

[dustinsandwich]

27 minutes ago, EDM620 said:

Those are the flashers. One is for the hazards, the other is the signals.

That's good to know thank you, except the flasher switch is hooked up and working. Except on the passenger side, same as turn signals. Should I bridge these and see if it makes the passenger signals work?

[dustinsandwich]

7 minutes ago, EDM620 said:

Search for a 720 factory service manual - years ago I managed to find one online somewhere (maybe here on Ratsun?) that will help you sort through the wiring.

 

There are peculiarities dealing with the OEM wiring for sure. While I cannot determine the issue with the 2 black relays you have, I have determined that the OEM Blue relay / headlight circuit doesn't follow normal logic IMHO. For example: a standard 5 pin relay is configured as below:

 

The weird thing I have recently discovered is that the 720 uses a fuse for the Left and Right headlights separately, yet the relay combines both and has 2 grounds. Having difficulty wrapping my head around that.

I actually managed to score a correct year FSM for $20 on ebay. Trouble is, I'm used to old school wiring diagrams with the whole loom laid out and this doesn't have the wire colors in the fold out diagram in the back, just references to individual parts. So I'm having a hard time tracing from wire to function and finding grounds.

[dustinsandwich]

30 minutes ago, EDM620 said:

The weird thing I have recently discovered is that the 720 uses a fuse for the Left and Right headlights separately, yet the relay combines both and has 2 grounds. Having difficulty wrapping my head around that.

That... is bizarre. Maybe for redundancy? 

[dustinsandwich]

54 minutes ago, EDM620 said:

Those are the flashers. One is for the hazards, the other is the signals.

Oh, I misunderstood. The cut ground wire is in front of the flasher units in the pic.

[Thomas Perkins]

Your 86 Nissan 720 manual is on Ebay waiting for you.49.99 with free shipping.

[EDM620]

12 hours ago, dustinsandwich said:

with the whole loom laid out

While different, there is greater detail in the FSM with the actual connectors identified and pin locations as well as colors.

This diagram shows the full lighting circuit. This is really helpful to trace an entire circuit as the connectors are defined by correct shape, Color (note "blue" connector), and if wire color changes from one side of connector to the other. Only the wires relative to that circuit are illustrated.

 

Elsewhere in the FSM it will show you where to locate the connectors - The blue connector is numbered and is shown where it is in the vehicle.

 

Also, the outer headlights are combination Hi/Low beams with 3 terminals each. The inner pair are Hi beam only thus only 2 terminals.

Here you can see the Headlamp relay that has my knickers in a knot as I was going to do something different.

 

Note the last Trouble Diagnosis line - Headlamps Dim - possible cause is a burnt fusible link. Check yours.

[dustinsandwich]

17 minutes ago, EDM620 said:

While different, there is greater detail in the FSM with the actual connectors identified and pin locations as well as colors.

This diagram shows the full lighting circuit. This is really helpful to trace an entire circuit as the connectors are defined by correct shape, Color (note "blue" connector), and if wire color changes from one side of connector to the other. Only the wires relative to that circuit are illustrated.

 

Elsewhere in the FSM it will show you where to locate the connectors - The blue connector is numbered and is shown where it is in the vehicle.

 

Also, the outer headlights are combination Hi/Low beams with 3 terminals each. The inner pair are Hi beam only thus only 2 terminals.

Here you can see the Headlamp relay that has my knickers in a knot as I was going to do something different.

 

Note the last Trouble Diagnosis line - Headlamps Dim - possible cause is a burnt fusible link. Check yours.

Okay, this is good, narrowing it down. I think the cut ground under the steering wheel must go to connector 121M on the headlight circuit. I see also that there's a ground at the negative terminal, which has been cut on my truck. I'll wire these to ground and see if that improves things.

[wayno]

As I mentioned, there are no grounds in the headlight circuit except for the ones involved with the relay, any ground added to this circuit messes things up big time, even adding a ground for the high beam indicator in an older Datsun dash screws things up, even that high beam light has two wires in the 720, neither wire is black.

Edited Friday at 07:02 PM by wayno

[wayno]

23 hours ago, dustinsandwich said:

That's my plan, the only problem I have is the first electrician made some splices that don't make sense to me. There are two green/blue wires that might go together, but I'm not sure because they both come from the some side of the loom, and then a red/yellow which has a splice into it.

i don't know where these are supposed to go, though when i bridged them the running lights came on.

 

The green wire looks added with a vampire device, I would remove it, the red wire I cannot see what color the wire is before the blue connector.

 

You will likely have to remove everything that has been added in the circuit to get the circuit to work properly.

 

A friend of mine had a 1982 Datsun 720 diesel wiring diagram expanded to a 4' by 8' size, he loaned it to me, and I hung it on my wall, using it I was able to combine my 1969 Datsun 521 dash into a 720 wiring harness, it took a lot of time and effort, but I cheated on the steering column stuff, I used all the 720 wiring involved on the column like headlights, wipers, hazards, and I deleted that 521 stuff.

Edited Friday at 07:27 PM by wayno

[dustinsandwich]

1 hour ago, wayno said:

red wire I cannot see what color the wire is before the blue connector.

It's connected to two green/blue wires, which might have more splices under the insulation 

[dustinsandwich]

2 hours ago, wayno said:

As I mentioned, there are no grounds in the headlight circuit except for the ones involved with the relay, any ground added to this circuit messes things up big time, even adding a ground for the high beam indicator in an older Datsun dash screws things up, even that high beam light has two wires in the 720, neither wire is black.

Yes, there's a black wire that grounds directly behind the turn signal flasher that's been cut, I suspect this should be going to the relay. I meant relay when I wrote connector. It's the black wire in this pic: 

Is that where the headlight relay grounds out?

[Thomas Perkins]

The price on the 86 FSM has dropped to 39.99.

[dustinsandwich]

1 hour ago, Thomas Perkins said:

The price on the 86 FSM has dropped to 39.99.

I appreciate it, but I already got a 1984 FSM.

[dustinsandwich]

Okay, I got the fuse block wires soldered to their correct factory pairs. It looks like the only bypass was the radio, which was just barely twisted and taped. Explains the inconsistent radio power.

 

I went looking for the fusible link, and it looks like maybe it burned out and was replaced with wire. I'm not sure:

[datzenmike]

On 10/3/2024 at 7:40 PM, EDM620 said:

The weird thing I have recently discovered is that the 720 uses a fuse for the Left and Right headlights separately, yet the relay combines both and has 2 grounds. Having difficulty wrapping my head around that.

 

The headlamps have their own separate fusible link. This feeds two fuses each supplying power to the left or the right lamps through the headlight switch. There is one ground at the headlight relay controlled by the hi/low beam switch. The relay grounds either the high or the low beams to turn them on.

[wayno]

23 hours ago, dustinsandwich said:

Yes, there's a black wire that grounds directly behind the turn signal flasher that's been cut, I suspect this should be going to the relay. I meant relay when I wrote connector. It's the black wire in this pic: 

Is that where the headlight relay grounds out?

 

I have no idea what that wire is for right now, keep in mind that I mostly deal with 1981/82 diesel harnesses, for gas engines I pick the 1980 720 harness with an L20b, I did put a later model 720 harness in a 1970 Datsun 521 with a Z24, but I was careful to not cut any wires, so there were no mystery wires to deal with except one ground involving the coils.

 

I will look at my flasher to see if my harness has a black/white wire in that area, hopefully I will remember to remember till I get home.

[dustinsandwich]

18 hours ago, datzenmike said:

There is one ground at the headlight relay controlled by the hi/low beam switch. The relay grounds either the high or the low beams to turn them on.

Where does the ground at the relay attach to the body?

[dustinsandwich]

19 minutes ago, wayno said:

 

I have no idea what that wire is for right now, keep in mind that I mostly deal with 1981/82 diesel harnesses, for gas engines I pick the 1980 720 harness with an L20b, I did put a later model 720 harness in a 1970 Datsun 521 with a Z24, but I was careful to not cut any wires, so there were no mystery wires to deal with except one ground involving the coils.

 

I will look at my flasher to see if my harness has a black/white wire in that area, hopefully I will remember to remember till I get home.

I appreciate it. I'm beginning to suspect that I'm going to have to comprehensively go through this harness and put everything to stock, piece by piece.

[dustinsandwich]

I found a random ground in the heater circuit. Now the heater and blower work.