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I need some headlight help


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I am hoping my scan is legible enough. This is the factory manual... I can probably enlarge parts if I need to. We are trying to get the light's working on Cody's wagon. Most of the running lights seem to work and the turns supposedly work per Cody but I haven't checked behind him yet. The problem is the headlights. He said they worked once and then not again. I have done some testing with a meter and both sides of the high beam lamp have battery voltage, that doesn't seem correct. I would think one would be power in and one would be ground. How can I have voltage on both sides?

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Thanks for the article, but 510's don't have a combo switch. They have a pull switch on the dash and relay (who knows where). There also must be power through the turn signal switch because I believe that controls high beams...

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I can try to break down the circuit for you.

The green/blue wire comes into the headlight switch. When the switch is in the #2 position, you should have 12VDC on the red/yellow wire coming out of the switch. That wire goes to the fuse box where it connects to the left and right headlight fuses. The left headlight fuse comes out to a red/blue wire. The right headlight fuse comes out to a red wire. They go out to their respective headlights. The red/black wire is for the low beams and goes back to the headlight relay. The red/white wire is for the high beam, and it also goes back to the headlight relay.

The positive for the coil voltage is green/blue. The negative for the coil voltage is black/red. The black/red wire goes to the turn signal switch where is open or connected to ground, depending upon the switch position. When the coil is de-energized, the red/black wire is grounded, finishing the circuit for the low beams. When the coil is energized, the contacts connect the red/white wire to ground.

So, if the headlight switch is on with the turn signal switch on low beam, how could you see 12 VDC on both sides of the high beams? If you don't have the ground at the relay, you only have potential voltage. The headlight elements acts as a piece of wire and not a load. That's why you see voltage on both sides. The voltmeter has significantly higher resistance compared to headlight element.

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Ok, so I worked on this some more today. Some previous owner has been under there hacking it up...<_< 


Here is the homemade choke relay that is evidently always hot!! straight to the battery...

I tried to upload some more but it is giving me an error...

I pulled the factory headlight relay that is on the rear side of the passenger side strut tower on the inboard engine side. There are two relays there, I don't know what the other one is yet. I removed all the nasty sticky electrical tape that someone wrapped the harness in and found some melted wires. I will try to post pictures later...

I traced the 2 black wires through the harness after I unwrapped it. I found a factory bond a little bit behind the battery. It looked good, like brand new. Took a meter and rang it out from the relay plug to the battery negative. Good continuity. so then I made a jumper wire out of a piece of 12ga solid copper. I tested the plug before jumpering it. With the headlights on I have 12voltls on the Red w/ White. I believe the high beam switch is the turn signal stalk. It moves forward and aft and stays in either position. Can somebody verify that. I couldn't ever get 12v on the Red w/ Black by itself. That may be a function of the relay. When I jumper between Black & Red w/ White I get headlights (High beams)

When I try to jumper between Red w/ Black and Ground I don't get low beams. I need to double check the low beam filaments are good. I don't remember if I verified that with a meter.

So at this point I believe the relay is bad. Was gonna replace that and see if I can get them to burn...

Does that make the most sense or should I rework them now to reduce the load on the switches? @SteveJ

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To ensure you have good voltage, I suggest hooking up a battery charger to the battery and set the charger to the lowest setting. Please record your steps and your meter readings. It's tedious, but it helps with diagnostics when I can't see what you're doing.

First, remove the relay from the wiring harness.

1. With the headlight switch on, at the plug for the relay, check voltage from the RB wire to ground. You should see 12 VDC (or whatever your battery voltage is). Also measure voltage from the RW wire to ground. You should also see 12 VDC.

If you have voltage on one wire and not the other, check continuity from the headlight plug to the relay socket on the wire without voltage.

You might also use an ohmmeter to look for resistance across the headlight elements with an open line/infinite resistance indicating a bad element.

2. Pull the fuse for the right headlight. Recheck voltages. Put the fuse back and pull the left headlight fuse.  Recheck voltages. Also while the fuse is out, check it for continuity, just to make sure the fuse is good.

These circuits are designed to backfeed between left and right on a blown fuse. That can make diagnostics tricky.

Once you have determined that the wiring is good up to the relay socket, you can turn off the headlight switch and jumper the RB wire to ground. Turn on the headlight switch. If you don't have low beams, pull the headlights and check for continuity between the pin for the RB wire and ground. Also check the voltage between the positive pin on the connector and the RB wire. Report the results.

Repeat the process above with the RW wire. Remember that you have to pull all of the headlights when you want to run the meter checks.

If we can't figure it out the go-around, heck, I might just drive up there in a couple of weeks.


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Baseline voltage 12.80v

On ‎7‎/‎10‎/‎2016 at 9:09 PM, SteveJ said:

With the headlight switch on, at the plug for the relay, check voltage from the RB wire to ground


On ‎7‎/‎10‎/‎2016 at 9:09 PM, SteveJ said:

Also measure voltage from the RW wire to ground


Checked fuses for continuity. Both are good...

On ‎7‎/‎10‎/‎2016 at 9:09 PM, SteveJ said:

Pull the fuse for the right headlight. Recheck voltages

RB 11.7v RW 11.71v

Lots of movement on the meter. Hard to make good contact. Voltages all over the place. I let it sit for a second and it settles at these voltages

On ‎7‎/‎10‎/‎2016 at 9:09 PM, SteveJ said:

Put the fuse back and pull the left headlight fuse

RB 12.07v RW 12.06v

On ‎7‎/‎10‎/‎2016 at 9:09 PM, SteveJ said:

you can turn off the headlight switch and jumper the RB wire to ground

I used the ground in the relay harness plug. All beams burn, which I assume is high beams because the inside lamps are high beams only, but they are not very bright even though the battery shows 12.60v with them on...

Same test with the RW jumpered I get the same results. On a whim I checked the voltage across the back of one of the high beams, it was barely glowing, 1.80v??

Are the low beams feeding back into the high beams looking for ground?

Edited by Patcon
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Ok I messed with this some more. I went through and redid the battery cables and the chassis ground at the voltage regulator. Some one had a red cable for the ground with some black electrical tape and a black cable for positive with some red electrical tape. So we remade all of those and cleaned all the connections at the starter. New connectors at the battery. Had the cover off the headlight relay and tried the headlights. No joy...They don't appear to burn at all. The high low switch seems to work because the relay moves and we can make it toggle with the high beam controls at steering wheel.


We have other electrical issues too :(:

Not charging

No brake lights

No wipers

No reverse lights

Half a dozen loose connections

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Well SteveJ came up today in the 260 and brought his little bag of magic tools. He was a big help. We narrowed down the headlight issue to a bad headlight relay. He had a replacement and all the vintage connections to make a plug n play fix. We still had an issue on the drivers side with glowing headlights we eliminated a backfeed issue and he narrowed the problem down to corrosion in the fuse box. So under his direction we pulled the fuse box and soaked the whole thing in a container of white vinegar for a couple of hours. After that a neutralization bath of water and baking soda. Blow it dry then use denatured alcohol to get all the water out. Blow it dry again. That brought the drivers side headlight leg up over 2 volts. Headlights are good now.

We found 2 bad fuses in the fuse box, after that we had brakes lights and wipers. We got the horns working and I swapped a voltage regulator and got the alternator working.

Then we had an erratic turn signal and I pulled the turn signal switch for cleaning...

All in all a really productive day, I may have even forgotten something...

Really big thanks to @SteveJ for coming up to help




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I was only too happy to help because it gave me an excuse to take the Z on a longer drive, and I got to help a friend by doing something I enjoy doing. I hope Cody was able to pick up on a few things. Speaking of which, have him read https://fiddlingwithzcars.wordpress.com/2012/12/22/relays-simplified/ to understand a little better about the headlight relay and why the substitute relay does the same thing. Now it's time to wash the road smell off of me and get the before photos of the turn signal switch.

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