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77 710 wagon no running lights and various other electrical curiosities


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Okay, I've searched, I've changed out fuses. I've cleaned the fuse box. I've tried a different light switch of unknown functionality. Still nothing.


Blinkers, break lights, and reverse lights work. Headlights work. No running lights. I'm terrible with wiring, and probably gonna get flamed, but hopefully the flames will point out something simple that I'm missing.


I've got power at the fuse box, but not after the switch. That is, if I'm testing the right wire.


Any help is good help. Even if you have nothing nice to say.

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First, fuses are not to be trusted. They can look good but have bad solder connection inside. I believe the right hand side top fuse (20amp) is for all clearance, side, tail and license lamps. (look on the plastic cover) Hold a quarter across the fuse holder clips.... do the lights come on? If they do the fuse is bad or not making good contact with the holder clips.



Second, are the dash lights working? They are on the same circuit and should be off... but if on, that means the switch is working and there is a problem somewhere between it and the chassis.


Come 'mon Texas, you need another point.

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I tried jumping the fuse with a piece of wire. Nothing happened. The dash lights are not on. That was how I discovered the tail lights not working. I was on my way to work, and noticed no dash lights. I knew that meant no tails, so I pulled over and checked to fuses.


I just got the headlights working last week by pulling the front of the wiring harness and cleaning every connection back to the fuse box.


Everything worked for a week, and then I lost tail lights day before yesterday.


I've been fighting the wiring on this car since I got it.

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I would think so.


The dash/tail/license plate/front and side markers are all on in the first pull out position of the headlight switch and the second when the headlights come on.


Try pulling the headlight switch out to the first position many times to clean the connections inside. try gently twisting the knob. Do the tail lights even flicker slightly??? If they do then it's the switch or the plug making poor contact.



We're still assuming is there that we can't see. So better get a test lamp and check that the light come on on both sides of the fuse... just to be sure.


Then pull the headlight switch. In the off position, there should be two wires with 12 volts on them. One for the headlights and one for the markers.


If there are, test the other wires for 12 volts when you pull the switch out to the first position. If one lights up the tester then the switch is working. If nothing then the switch is not making contact inside.




My 620 headlight switch did this. (not saying they are exactly the same but probably similar) With it removed I carefully bent the metal tabs back just enough to disassemble it. The brass contacts inside were all corroded. I cleaned them and greased the sliding parts and carefully put together abd bent the tabs back in place to hold it... bingo it worked. Have a care, as the tabs will bend once or maybe twice but they are soft and will break off.

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The 710 and 620 switches are exactly the same and interchangeable. I'm using a multimeter to check voltage. I will try both sides of the switch and check back. I think it's the switch, but when I tried a 620 switch, I still had the same issue. I haven't been able to get as much as a flicker since they stopped.


Gonna do more testing and check back. I'm sure it's either the switch, or a wire close to the switch.

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Ok, so I'm working on that testing and, My headlights are on in both the park light position and the headlight position on the 620 switch. On the 710 switch, nothing happens in the first position, but the headlights come on in the second. I'm thinking the 620 switch is bad. Still testing the 710 switch.

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Problem solved. Bad spot in the wire a foot or so after the switch. I also replaced the switch with one from a 620.


The 710 switch had a plastic box which was quite broken. The 620 box is metal and a bit sturdier.

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Another issue. The 620 switch is wired differently. In position 2, all lights are on. In position 1, the running lights turn off, but the headlights stay on. Backwards of how it should be, but it's easy to move the wires around on the 620 switch.

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  • 2 weeks later...

Ok, so now my headlights are out again. This time it's the headlight relay. Atleast that's what I'm calling it. It's a little box behind the battery. I've got power going in, but not out.


My issue is, the one on the car is a simple 4 prong plug. I looked it up on rockauto, and the relay in the picture has much different prongs.




My question is, can someone get me the part number for the 4 prong one in my car? Maybe mine's been replaced by one of the POs, but it fits nicely in the metal box and looks like it belongs there.


Thanks in advance for the help. Im not sure where to find part numbers for this car, as I still don't have a fsm for it.

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This is just a picture for example and definitely NOT for a 710. These were more likely used after '80. Order by year and you will likely get the correct one.



I find it curious that the headlights are not on. The relay can only be in one of two positions high or low beam. Very unlikely it can fail in between. Power is already at the headlights from the headlight switch, or should be. The relay selects the one that it's going to ground, to turn on. No ground... no headlights.

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The other relays that are advertised on rockauto have the same prong setup with different pictures. They're usually pretty good about using the oic of the part you're buying. Thus my concern.


I could be wrong about what the problem is. As I've stated before, I suck with wires. My multimeter says I've got power to the relay, but not after, so I thought it must be the problem.


I was driving home from work the other evening and the lights just went off. I tried various switches and nothing happened. Ive got tails, running lights, and all signals.


The only other curious thing was, earlier the same day, with the headlights off, the engine sputtered and acted like it was running on 2 cylinders. I pulled over, and it just fixed itself. This was about an hour and a half before the lights went out.


Maybe not related,but I attribute it to wiring problems.

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I already checked the wires at the fuse box. There's no power coming into the fuse box. According to the wiring diagram, there is a " Brown fuseable link" between the battery and the fuse box.

This relay was all I found. There is power before it, but not after. The wire out of it leads to the fuse box.


I'm not sure if this is the OEM setup as there was some electrical tape in between. This car has had a lot of electrical work done by POs. It was a parts car before I bought it. Now it's my dd. That's why I'm concerned that I'm buying the right part.


Thanks again.

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