720 headlight hi beam

[Hdb720]

I I'm new here was hoping for some help I own a 85 720 pickup my headlights turn on but my high beams are constantly on but not at full blast most of the time they are on about 30% power they go up and down in brightness max is about 60% until I turn my high beams on then they turn on all the way on

[datzenmike]

Do you have after market head lamps with replaceable bulbs????

 

 

 

Try replacing the two fuses on the far right hand side of the fuse box, the side closest to the engine. Fuses are cheap and really not to be trusted on looks. See if that changes things.

[Hdb720]

I am using 76 710 headlight no after market bulbs I was planing on going to after market bulbs I will replace the fuses I thought it might be the relay aswell

[wayno]

The 76 710 had round headlights, the 720 has square headlights, the bulbs are wired differently, you have to change where the wires are in the 720 headlight plugs or make pigtails.

[datzenmike]

I wonder if that would be the problem??????

[Hdb720]

Shouldn't the head lights not work at all I tested the voltage and every thing lined up the way it should Befor I plugged them in

[datzenmike]

Well for one thing, the 710 has one side of all the lamps grounded and sends power to either the high or the low beams.

 

The 720 sends power to all the bulbs and selects a ground path for either high or low beams.

 

 

The rectangular bulbs are wired differently than the round ones. The high and low lamps have a single wire in and a shared common out. On the 710 the shared common wire is grounded. On the 720 this common wire has 12 volts on it. To convert for use on the 720 the left and right wires must be pulled out of the plug and swapped. On the 720 wiring this would be the Red/Black and Red swapped on the right outside plug .... and the Red/Yellow  and Red swapped on the left outside plug. Now round bulbs should work normally. This is what I did.

[Hdb720]

Well for one thing, the 710 has one side of all the lamps grounded and sends power to either the high or the low beams.

 

The 720 sends power to all the bulbs and selects a ground path for either high or low beams.

 

 

 

 

The rectangular bulbs are wired differently than the round ones. The high and low lamps have a single wire in and a shared common out. On the 710 the shared common wire is grounded. On the 720 this common wire has 12 volts on it. To convert for use on the 720 the left and right wires must be pulled out of the plug and swapped. On the 720 wiring this would be the Red/Black and Red swapped on the right outside plug .... and the Red/Yellow and Red swapped on the left outside plug. Now round bulbs should work normally. This is what I did.

I just did a tap test and the passenger bulb went out I had a friend tell tell me it might be a burnt out bulb with the filament crossing over to the high beam in that bulb now I have to order headlights because no one here carries 5 3/4 headlights

[datzenmike]

That is another possibility. But the bulbs are still different internally between round and square.

[Hdb720]

That is another possibility. But the bulbs are still different internally between round and square.

I have to do the bulbs I'm hoping this fixes it but if not I'll rewire

[wayno]

I did this a long time ago when I put a 720 wiring harness in my 521 kingcab, I have done it at least 3 times since including changing my 720 turbodiesel to round headlights, you cannot just plug the round headlights in and expect them to work, the ground is in a different place.

Your problems started when you plugged the round headlights in, I do not recall which wires need to be switched at the moment.

[Hdb720]

I did this a long time ago when I put a 720 wiring harness in my 521 kingcab, I have done it at least 3 times since including changing my 720 turbodiesel to round headlights, you cannot just plug the round headlights in and expect them to work, the ground is in a different place.

Your problems started when you plugged the round headlights in, I do not recall which wires need to be switched at the moment.

Nice truck

The headlights worked with out rewire the high beams just kinda were on in a low way like I candle but Befor I killed my passenger low beam completely when I was tapping on it the high beams would get brighter and dimmer with the tapping

[wayno]

If you turn everything off and wait for dark I believe you will find a couple of the headlights barely on, it will drain your battery overnight.

I just went out and looked, the high beams(inner lights) are fine, but the regular lights(3 wires) are the issue, the 3 connections to the light are shaped like a "U", the bottom of the "U" is correct, the other two need to be switched and then everything should work properly.

If you were to unplug the outside headlights, the inside ones would likely work properly, but since the outside lights are wired differently than the square headlights, it screws everything up, oh and the high beam indicator light also plays a part in this, if it is disabled I believe the drain goes away, but that might only be when used with a 521 instrument cluster.

[Hdb720]

If you turn everything off and wait for dark I believe you will find a couple of the headlights barely on, it will drain your battery overnight.

I just went out and looked, the high beams(inner lights) are fine, but the regular lights(3 wires) are the issue, the 3 connections to the light are shaped like a "U", the bottom of the "U" is correct, the other two need to be switched and then everything should work properly.

If you were to unplug the outside headlights, the inside ones would likely work properly, but since the outside lights are wired differently than the square headlights, it screws everything up, oh and the high beam indicator light also plays a part in this, if it is disabled I believe the drain goes away, but that might only be when used with a 521 instrument cluster.

 

I have been driving it like this for probably 7 months other than the high beam problem I haven't had any battery drain problems and my lights turn off completely

[wayno]

I have been driving it like this for probably 7 months other than the high beam problem I haven't had any battery drain problems and my lights turn off completely

As I said, that might have been a 521 instrument cluster issue, as the high beam indicator is grounded on the 521 instrument cluster, while it is not grounded on the 720 instrument cluster therefore causing a drain.

Fact is round and square headlights have the ground wire in a different spot, you having problems just confirms the issue if you are using round headlights on your 720.

[Hdb720]

As I said, that might have been a 521 instrument cluster issue, as the high beam indicator is grounded on the 521 instrument cluster, while it is not grounded on the 720 instrument cluster therefore causing a drain.

Fact is round and square headlights have the ground wire in a different spot, you having problems just confirms the issue if you are using round headlights on your 720.

After I put new bulbs in it I'll find out if I'm still having the problem now I'm at a stand still because no one near me sells them

[Cheetosrdabest]

Had the very same problem when I changed to replaceable bulb headlights....couldn't figure it out so I changed the high beams back to sealed beams (stock) and the battery drain went away. The low beams are still replaceable bulbs. Never did figure out why the wiring was different but something is different about the wiring for sure.

[wayno]

Let me say that I am talking about stock type round(pre 1980) and square headlights(1980-86 720), I don't know about specialty lights.

When I changed my 720 over to round headlights I made pigtails and switched the wires as I knew what would happen if I didn't, I have had no issues, everything has worked properly since.

[Hdb720]

Let me say that I am talking about stock type round(pre 1980) and square headlights(1980-86 720), I don't know about specialty lights.

When I changed my 720 over to round headlights I made pigtails and switched the wires as I knew what would happen if I didn't, I have had no issues, everything has worked properly since.

thanks for the info I'll keep it in mind

[Cheetosrdabest]

Let me say that I am talking about stock type round(pre 1980) and square headlights(1980-86 720), I don't know about specialty lights.

When I changed my 720 over to round headlights I made pigtails and switched the wires as I knew what would happen if I didn't, I have had no issues, everything has worked properly since.

You have one of those cool little trucks that i have yet to even see one on the road !!! I've been in so many countries and still cannot find one I can acquire :)

[wayno]

You have one of those cool little trucks that i have yet to even see one on the road !!! I've been in so many countries and still cannot find one I can acquire :)

Thankyou, but I have so many trucks, which one are you talking about?

[Cheetosrdabest]

The one in your forum pic. Not sure which model # it is, but man it is awesome ! I have watched the roads in Brazil, Mexico, Turkey, France, Germany, and (of course) the Southern states in the US, but still have never seen one

[Cheetosrdabest]

I'm actually in Mexico this week and have seen tons of the 720's ( dually's, 4 doors...they are everywhere down here that are hard to find in the US ) but not the generation before the mid 80's which I think is one of yours

[wayno]

If your talking about the red/black vehicle in my avatar, that is a 1964 Datsun NL320, the 320s were made from 1962 thru 1965.

[Charlie69]

Wayno doe this truck have AC?