98 v70 turn/brake light problem. MVSOLVED. Bad ground wire

[mikealder]

Replace the defective cable and ring tong tag, you can either solder the new cable to the old one above the break in the wire or use a screw style junction block and you problem will be dealt with - Poor earths for the rear lights can cause all sorts of interesting illuminations of the rear lights, once correctly grounded the fault will clear - Mike

[98v70dad]

Is there a quick temporary repair anyone can suggest for that defective ground wire short of replacing it? The E8 earth point grounds both sets of lights in the left tail light (5 bulbs I think). This is my daughters car and I don't get much time with it on weeknights. The car gets home 30 minutes before dark and my work space is the driveway ...I don't want to try doing the permanent repair in the dark. On the weekend I can do a proper repair but I don't like her operating the car for the next few days with the rear lights acting up. I was thinking of somehow running a jumper ground wire from somewhere near where the wire harness connects to the bulb holder (2 locations) and attaching them to the E8 earth point with a ring connector similar to the stock wire. I don't really want to cut the original ground wire yet so tying into it near the top end temporarily is the thing I need some ideas on. I've seen mechanical splices and don't consider them suitable for permanent but they'll do for a couple of days.... any other thoughts? BTW thanks again everyone for the advise. I HATE working on electrical and probably always will ... that said I gotta fix it, the volvo people charge way too much!

[98v70dad]

This may sound like a stupid question but I'm not too good on electrical. Now that everyone has helped me isolate the problem I'm not too sure how to fix it. I threw out a proposed temporary fix and didn't collect any comments on it. The obvious fix is to replace the ground wire. That's easier said than done due to multiple branches grounded by the same wire and its all buried in a big bundle. Someone commented that I could solder on a new round wire at the break. The problem is I don't know any techniques for finding the break. How exactly is that done other than by feel. I have a continuity tester but when you're dealing with a big wire bundle it really doesn't isolate the location of the break, ... it just tells you that you have a break somewhere between the two ends.

[JimBee]

You know where one nd of the wire is. Then it disappears into the bundle. Where does it emerge at the other end? The wiring diagram will help you find that point. It must go onto a bus or into the fuse box or a relay socket. If you can find that end, then you can replace the wire.

You can get puncture type leads for your circuit tester. Radio Shack might have them. They have a pin that can go through the wire's insulation. Lacking the real thing, you can use a pin. Just stick it into the wire and put your alligator clip on it.

I suspect the break is near where you were wiggling the wire. The insulation on these wires is pretty tough. You could use a utility knife and slit the tape binding to at least open up the bundle further back. Then do a pin test from that point to the ground (end) point. Shake the wire. See if you can get it to break continuity along the segment you're testing. You might need a helper.

If you can isolate the point, then cut the wire upstream from that point and run a new segment from there to the end. Don't worry about elegance. You can tape the new segment to the bundle.

Last year when I was having fits tracking a faulty circuit, I made up a 10 foot long test lead from an old piece of lamp cord to which I attached 4 alligator clips from Radio Shack, then took that along with my wiring diagram to the junk yard and literally tore apart the wiring from a junk 850. I opened the fuse box from beneath, undid bundles, etc., keeping careful accounting of what i was finding. I used my multimeter to test continuity from fusebox to end point connections. Nothing I dug into had recycle value for the junk yard (though I bought some relays and miscellany while I was there). I learned the circuilts, made notes on the diagram and eventually figured what it HAD to be. And it was. Perseverance is the key.

Stay on it. You'll solve it.

[BEJinFbk]

This may sound like a stupid question but I'm not too good on electrical. Now that everyone has helped me isolate the problem I'm not too sure how to fix it. I threw out a proposed temporary fix and didn't collect any comments on it. The obvious fix is to replace the ground wire. That's easier said than done due to multiple branches grounded by the same wire and its all buried in a big bundle. Someone commented that I could solder on a new round wire at the break. The problem is I don't know any techniques for finding the break. How exactly is that done other than by feel. I have a continuity tester but when you're dealing with a big wire bundle it really doesn't isolate the location of the break, ... it just tells you that you have a break somewhere between the two ends.

Going by the wiring diagrams, There's a separate ground for each side.
That's why I'm not convinced it's your problem. Stuff like this usually
happens where the wires come together from both sides to a common
ground point. The connection to ground gets funky and the lights sharing
that ground begin providing rogue ground paths for each other.

The problem you describe doesn't fit this set of circumstances.
But, just for grins...

It's a short run from each tail light to the corresponding ground point right there in the D pillar.
They can't be more that a foot or so long. Start with a loose piece of wire and just parallel the
existing wire. Make a temporary connection at the connector where the ground is provided at
the taillight and ground the other end. All you're doing is giving it a known good path to ground
so you can see if that solves your problem. If it does, you know where the trouble is.

[98v70dad]

Yeah unfortunately thinking about it troubles me a little. I can't explain why a bad ground on the left side would cause lights to come on dimly on the right side. I'm not convinced either thats why I wanted to try a temporary jumper like you suggested. Its easy and wont take me hours of troubleshooting and will either prove the point or not. I have years and years of troubleshooting airplane problems at my old job but I'm a mechanical, structural, hydraulics sort. I left electrical to the electrical guys. Unfortunately, for my 98 V70 I am the electrical guy and I've spent years of trying to solve it. At least I know that by wiggling the wire bundle and or ground wire in about a one foot area I can make to problem come and go. Somewhere in that one foot of bundle something is either loose or broken. its still a big job to find it but now I have some hope.

[98v70dad]

Yeah unfortunately thinking about it troubles me a little. I can't explain why a bad ground on the left side would cause lights to come on dimly on the right side. I'm not convinced either thats why I wanted to try a temporary jumper like you suggested. Its easy and wont take me hours of troubleshooting and will either prove the point or not. I have years and years of troubleshooting airplane problems at my old job but I'm a mechanical, structural, hydraulics sort. I left electrical to the electrical guys. Unfortunately, for my 98 V70 I am the electrical guy and I've spent years of trying to solve it. At least I know that by wiggling the wire bundle and or ground wire in about a one foot area I can make to problem come and go. Somewhere in that one foot of bundle something is either loose or broken. its still a big job to find it but now I have some hope.

[abscate]

Quick answer to that ground problem

Turn signal lights are isolated left/right, but taillights are not. If the LH turn signal ground is bad but still makes contact with the common tail light ground, the current flows through the turn signal bulb, through the common ground over to the right hand tail light and lights it if the voltage different from the positive voltage on the other side. Since the voltage drop usually isn't the full 12 VDC, the bulb lights dim.

If you google trailering forums, especially boats, you will find PetaBytes of Posts on bad tailight grounds causing wierd combination of lights...here is a typical cut and paste...

Strange Trailer Problems
It's very difficult to get people to check the ground connections, even though most trailer problems are probably caused by bad grounds. Some of the strange symptoms of bad ground connections are things like: the lights on the wrong side of the trailer come on; the lights on one side are brighter; the lights are on, but they're dim. Here's what's happening when these type of symptoms show up. Some of the bulbs on the trailer have two filaments in them.

One filament is for the running lights, they other is for the turn/brake lights. Each filament has a wire going to it. Both filaments use the same return, the base case which is connected to the vehicle's frame or ground. Under normal situations, current (hole current) flows from the positive terminal of the battery, through the wire to the filament, through the filament, through the base, through the ground, through the vehicle frame back to the battery negative terminal.

Okay, what happens if the ground connection is bad. Well, current (hole current) flows from the positive terminal of the battery, through the wire to the filament, through the filament, through the base. Okay, it can't go out the ground because the ground is bad. So, what happens? Well, it goes back from the base through the other filament, through the wire to the bulb on the other side of the trailer, through that filament, through that base, through that ground, through the vehicle frame back to the battery negative terminal. When all this happens, the filaments won't have the full voltage across them, so they will be dimmer, but on one side two filaments could be lit and that should appear brighter unless the other side filament is the brake filament. Okay, you get the picture. When things start appearing to be real strange, start looking at those ground connections.

In summary, trailer wiring problems can appear to be complicated. However, a systematic approach based on eliminating things that are proven good can help you focus in on the real problem. Also, when things start really appearing strange, start checking ground connections.

[98v70dad]

GOOD NEWS (for me)! I think I've finally fixed the rear lights problem on the 98 V70. I took apart the wire harness on the drivers side tail lights and found that the ground wire from the brake light was frayed to the point that less than 1/2 of the strands were still intact. I also found that the protective plastic sleeve around the wires had become hard and nearly broke off another wire. I fixed both of these spots with solder and shrink tubing and replaced the hard protective sleeve with multiple wraps of electrical tape. I drove the car for a few days and the lights would still go out when going over a speed bump. So, I finally got out my wallet and bought 4 new bulb holders AND all new OEM bulbs. Its been working now for weeks without a problem. FYI, I have found many almost broken wires at the edge of that corrugated black plastic protective tubing. Apparently it protects the wire until it becomes brittle enough forthe wire to press against and eventually break off. Hope this info helps someone else. I have never spent this much time and effort trouble shooting something.

[BEJinFbk]

Excellent! It's always a great feeling when you finally chase these down. Congrats!