Chevelles.com banner

1 - 20 of 24 Posts

·
Registered
Joined
·
23 Posts
Discussion Starter #1
Guys, I could sure use some help here. I'm melting the #20 red wire from the horn relay back into the fuse black connector. I don't know what happened to cause this. I've gone through my factory manuals trying to do a wire trace, but all the schematics in the manual are different than mine.
It worked last week. I replaced the trans and all was fine except the headlights, tail lights both quit. I probed the headlight socket and had power but no light. I thought it's a ground. The manual shows grounds coming off the low beam connectors, wrong. Mine goes back into the fuse box. Anyhow, it melts the red wire! Any thoughts or directions out there?

Thanks
 

·
Registered
Joined
·
7,762 Posts
GM didn't run headlight grounds back into the bulkhead connector (fuse box). There is no reason to. Not sure what you are looking at.

Normally there's only 2 wires running back to the bulkhead connector from the horn relay. 1, large #12 wire for interior power. 2, Smaller #20 horn button wire. You have an ammeter in that car?
 

·
Registered
Joined
·
23 Posts
Discussion Starter #3
John,
Thanks for the response. I have through the manual several times comparing my harness to theirs. The harness on my car does indeed have a ground wire from the light connectors which runs back into the fuse box, is turned back out into the engine compartment and goes to the sending units. Crazy as it sounds, it is true.
What I did yesterday was to splice into this wire coming off of the left headlight and ground it. I now have headlights but still no tail lights so it must be a missing system ground. The melted red wire I now think came from a friend trying to help.
What do you think, is it a ground?

Thanks
 

·
Premium Member
Joined
·
2,173 Posts
Let's talk about the ground straps between the engine and the body...... No No, on second thought, let's not. :D

Tom, dedicated grounds were typically used on cars that had extensive use of plastic in light and dash housings etc. These weren't prevalent until much later than the 60's. And, they normall only ran to the nearest body or frame ground (return) point. However, if you say you have them, so be it. It would be a first for me and I worked on 65's when they were NEW.

Since this happened after a tranny swap, did you do anything under the dash near the steering column or brake pedal. Did you pull or twist the harness feeding thru the firewall at the large connector. Pull it apart and check it closely. That's the only thing I can imagine that is common to all this. The headlight circuit is entirely separate from the tail light circuit. So are the grounds (normally). If the headlights are on a dedicated ground, maybe the tail lights are also. None of this makes sense for a 65. That's why we're scratching our heads.

Do you have any power to the lights (any lights) at the rear of the vehicle? After you make absolutely sure all the fuses are good, use a 12v test light with the ground clip connected to a long piece of # 12 wire running to the negative side of the battery. You can even use one side of a pair of jumper cables for this. Remove a tail light bulb and carefully (put electrical tape around the test light probe except for the very end) probe each contact inside the socket with the headlight sw. pulled on, the key on and the turn signal for that side turned on. If the test light flashes or lights, then you know you have an open ground. If it doesn't, you have a supply problem and it's common to the brake and parking lights. That would normally point to a fuse, block, harness or connector problem. I can't recall on the 65 but later models ran the rear lights thru the body harness from under the dash and inside the cab and trunk. Since it's not near the transmission, I would suspect a fuse or harness connector problem or a shorted reverse switch/harness.
 

·
Registered
Joined
·
23 Posts
Discussion Starter #5
Herb,

The shop manual shows dedicated grounds. Thats were I Became confused as the harness does not. I replicated the harness to the manual which then gave me head lights.
Now, I do have brake lights yet there are no running or license lights.
I'm sure it's in the ground circuit. I like your suggestion of testing the circuit with the test light grounded to the battery.
When I removed the transmission there was only one ground attached to a trans bolt. As I write this I now realize I should have inspected it for connection. There was nothing disturbed under the dash during the trans removal.
I will get after it and advise you what the outcome was.
Thanks so much for the help.

Tom
 

·
Premium Member
Joined
·
2,173 Posts
OK, that's better, brake/turn signals but no running lights. That circuit is common to the headlights in that it is switched by the same switch. Check the tail light (as opposed to brake ight) contact in the bulb socket. If you have power there, it's the ground (return) circuit. If not, it's a supply problem. You probably have it figured out but sometimes it's easier to open a tail light than crawl under the car. If it is a ground/return, I personally would do the same thing you did for the headlights. then I would bond (ground) the heck out of my body/engine and frame.

We've had several interesting discussions here in the past couple of weeks on this subject (that's why my opening comment). Just do a search on this forum on my name. I'm a believer in multiple ground straps between engine, frame and body with a solid clean connection of the negative battery cable to the engine. Others prefer the factory use of a single small ground wire to the rad support or inner fender. In your case, it wouldn't matter since you seem to have long-run dedicated grounds so each one (IMHO) is a potentially greater source of failure (as you are finding out). (perhaps not since each local ground also must be solid and clean) I just believe that there is no such thing as too many grounds on a vehicle. Just make darn sure that negative cable is bolted clean and solidly to the block. Let us know what you find.
 

·
Registered
Joined
·
7,762 Posts
Herb, you're doing fine. Ask him if he has dash lights.
The headlights and tail lights aren't common to each other. Each one is fed by a different input wire to the switch. The dash light input is the same as the tail lights.
Just thinking. If the rear brake/signals work, wouldn't the bulb have a ground?
 

·
Premium Member
Joined
·
2,173 Posts
Yeah lyou're right John, I thought about that after I posted. I agree about the tail and head lights not on a common circuit, just physically located on the switch body. Maybe if someone snagged a harness or jerked a wire ....

Given the unusual config. of this one, I'm hesitant to assume, but you are correct about that bulb ground. It indeed is common to both elements. Thanks.

It's starting to sound like supply, maybe fuse or harness, don't you think?
 

·
Registered
Joined
·
7,762 Posts
Or a junky fuse clip. Tom needs to answer your question about the dash lights. Sort of shows the path to wander down.
 

·
Registered
Joined
·
23 Posts
Discussion Starter #10
All,

I'm sorry I've not been able to address any of the suggestions yet, we've had a death in the family.
The dash lights have worked along with the dome light. As I mentioned, I did have brake lights.
Since adding a ground to the front head light harness, I now have head lights but still no tail lights.
The harness to the tail section is new. I had to create one as the original was fried.
So, from the help I've gotten so far, I will check out the following;
1. Check the tail section with a test light grounded to ground on the battery.
2. Double check the ground in relation to the transmission r&r.
3. Clean the connector again.

I'll try to get back with all of you this evening.

Thanks,
Tom
 

·
Registered
Joined
·
23 Posts
Discussion Starter #11
All,

As I mentioned earlier I now have head lights. I had to put a ground into the harness coming off the left head light.
I do have dash lights and I do have brake lights. I do not have running lights or indicator lights.
Per Herb's suggestion I tested the tail light socket with a test light. It flashed. I then added a ground strap from the frame to the body and it made no difference.
Guys....Is the fisher body cable grounded through the light switch? Is ther a ground line in the fisher body cable? Is the light switch ground through the tin shield attached to the dash bezel?
You all have been really great and I've learned a lot. Thanks, Tom
 

·
Premium Member
Joined
·
2,173 Posts
Tom, that's interesting. did you probe each contact in the socket? Did the test light glow from BOTH contacts or just one. One contact is the brake/turn signal, andone is the parking light. These are two different circuits in the same bulb that should use the same ground. Unless you ONLY had the headlight switch pulled, you may have been detecting the turn signal/brake light circuit, which you already said worked. My fault for not narrowing the test procedure after you said you had brake and turn signals. The turn signal is actually the flashing of the brake light circuit to the bulb element on that side of the car. You can't normally have turn signals without brake lights (and visa versa).

I guess the best way to narrow this thing down is to use the tag light as the test subject since it is only connected to the tail light circuit. (I'm betting you have a supply problem (perhaps a blown fuse) since the brake/turn signals work. That would indicate the ground is good since it is common to BOTH elements in the bulb. You can't separate them.)

Here's the test, using the same test light set up with a "home run" ground to the battery, turn the parking lights on, leave the key off and make sure nobody is stepping on the brake pedal. See if the front parks are on to insure the parking light circuit is getting power thru the switch. It is a totally different circuit from the headlight circuit. They aren't even tied together in the switch or have the same supply. To the best of my knowledge (John can verify), GM never switched the return on tail lights, only the supply. (but then, I never heard of of dedicated ground circuits in a 65 either.) So I'm not able to answer your question about grounds thru the light switch, but I doubt it is the path for the return. I believe that dome lights are the only lights that the switch makes the return circuit (ground) when activated.

Back to the test, probe the contact off the tag light socket. If there is no power in the tag light socket, and you are sure the harness is good, (or if the front parkinglights are out too) you have a supply problem. I would start at the fuse, then the switch and then trace the circuit thru the body harness to the tail and tag light to find out where the power is missing or being interupted.

If the test light glows when you probe the tag light socket contact, you have the ground (return)problem we discussed earlier. Again, since you have brake lights, I believe the ground is good for these sockets.

It's also time to check that ground connection on the transmission. Consider grounding each tail light and tag light socket to the body. The advantage of this is that if only one tail light is out, you know it's the bulb or ground for that fixture only. Also then if both tails and the tag were out, it would be a supply problem.

Again, sorry for not narrowing the test down earlier. Let me know what you find from the above test.
 

·
Registered
Joined
·
23 Posts
Discussion Starter #13
Hello Herb,

So good to hear from you.
The front parking lights are good. Following you directions to test the tail lights the findings are; yes to brake and turn signal. NO to parking lights.
I have revisited the ground at the transmission.
I have also added a ground strap from the frame to the body (1 inch wide), still no results.
Yep, I'm pulling my hair out.
 

·
Registered
Joined
·
7,762 Posts
Can I ask if the front park (running) lights are out? I assumed they were not working.
Also won't suspect a fuse because the dash lights are working. Both the dash lights and running lights share the same input 12 volt wire on the head light switch.
No, there's no ground switching in this circuit.
Yes, there is a ground ring or lug on the head light switch. It only has one purpose. That is, it provides a ground to operate the dome light when you rotate the rheostat over to the "clicked" position.
 

·
Premium Member
Joined
·
2,173 Posts
Hang in there Tom, we'll get this. If I can't help, you have John and Dean for a safety net.

I wish I had my old wiring diagrams for that car so I could point you to the source. You need to know that there is 12v feeding the rear tail light circuit in the body harness. You say you have front parks so there is supply from the switch. The brake/turns work so the ground should be good. It's sure pointing to supply into or out of that body harness. Wait a sec, isn't there a seperate connector in the trunk just for the tail/tag lights?

John, can you help with that? I'm working from memory here.

"rear tail light circuit" ?!?!?! as opposed to what, a front tail light circuit? I'm getting a headache
 

·
Registered
Joined
·
7,762 Posts
Ok, but my break time is getting cut short.
Tom if you have the schematic the circuit should look something like this. Bear with me if I'm off a little.
1, On the headlight switch there's a terminal with 2 brown wires crimped together. This is the running light output from the switch. One wire for the front lights and one for the rear lights. Assuming since the front lights work, the crimp is ok at this point and both brown wires have power on them.
2, The rear brown wire runs down to a connector near the steering column. From there, it plugs into the intermediate flex cable running under the rug.
3, Intermediate cable exits inside the trunk. From there the rear lamp harness plugs into it and the brown wire heads over to the lamps.
Think I would pull the running lights on. Unplug the connector inside the trunk, and measure the lead of the intermediate cable that the brown lead plugs into.
If there isn't power on that end of the harness, check for power on the intermediate harness connector under the dash.
 

·
Registered
Joined
·
23 Posts
Discussion Starter #17
Guys,

Being I have turn and brake lights, does that mean there should be power there for the running?
If the answer is yes then there should be power at the front connector (the fisher connection) under the dash. If there is no power for the tail lights at the fisher connector would that mean a bad ground or bad light switch or `am I still an apprentace and should cloud things up?
 

·
Registered
Joined
·
23 Posts
Discussion Starter #18
Sorry John,
Looks like we posted at the same time.
Looks like your pretty much saying what I asked.
If I have power at the brown line at the light switch then the switch is good, and I should follow the flex cable back through the trunk.
Guys, I'll get on it right now.
Thanks again for the help. I'll let you know what I find. Heck, if it works you'll all probably hear me!
 

·
Registered
Joined
·
7,762 Posts
The switch can be considered good because the front running lights come on. There is a small possibility that one of the brown wires (the rear)is not making a good connection at the switch. Probably the last place I would check.
 

·
Premium Member
Joined
·
2,173 Posts
Tom.

Running lights and brake lights are on 2 differnt wires (circuits). Having power to the brake lights has nothing to do with having power to the "running" (tail) lights. Like John said, you could check for power at the connector in the trunk (possibly under the rear seat) on the brown wire. This is about the middle of the circuit. (This is standard electrical circuit troubleshooting technique, start in the middle of the circuit and work toward the source of the problem. If there's no power in the middle, you know the problem is "up stream" of the test point. If there is power there, the problem is "downstream" from there.) The "downstream" end of that wire goes to the tail light and tag light bulb elements. If you probe a tag light socket contact (the "downstream" end of the circuit) and the there is no power there with the parking lights on, that connector (or the one under the dash) is the next point to check going towards the front of the car and the voltage source, the switch (in other words, upstream). An alternative is to check the end of that harness under the dash for power on the brown wire. If it's not going into the wire harness at that point, it isn't going to be comming out of the harness at the end near the trunk. This wouldmean the break of disconnect is between the front connector and the switch (or at the switch).

The terms "up stream" and "downstream" are used for a reason in circuits. Think of it this way, (don't get offended, you may know this but I'm just trying to help. I also can't helpit, I used to teach DC fundamentals) the brown wire is like a water pipe. 12 volts of electricity (water if you will) is put into the pipe at the switch and flows thru the pipe (wire) thru the tail and tag light bulb elements, then to ground (at each bulb). That's what makes the bulb element glow. (again, the tail light element is NOT the same one as the brake light element. If there is a break in the water pipe (wire), (12 volts of electricity) doesn't get to the bulb elements. If there is a short, it goes to ground before it gets to the bulb and blows a fuse or melts the wire (you already know about this )or does both. If the ground circuit is open, it can't "flow" and therefore won't light the bulb element. Since there are at least 4 connections between the switch and the bulbs:
1. at the switch
2. first connector into the flat body harness
3. 2nd connector out of the flat body harness
4. contact at the base of the bulb in the socket
The 5th and equally critical connection is from the bulb base (the brass part)to ground, also called the return since it must be connected by a wire or the body/frame/engine and negative battery cable and to the negative side of the battery so all the electricty must flow back to the battery.

Any one of those 5 connections may be open or the wire could be broken. The only way to know is to see if there is 12 volts going into that brown wire to find out where it's dropping out on it's way to the tail light bulb. Of course, if it's broken at or near the switch, there won't be any power in the brown wire at the connector under the dash. We know it's available at the switch terminal cuz the front lights work. BUT, they are on an entirely seperate brown wire. They are both tied together at the switch terminal.

One other (hopefully not insulting) point. If you hold a number 1157 tail light (not tag light) bulb up to the light, you will see 2 elements (or filaments) in it. One is for the tail (running) lights, the other is for the brake light. That's why there are 2 contacts on the base. These are 2 separate circuits, fed by 2 different pipes. Power to one has nothing to do with power to the other. The only thing common is the GROUND which is the base of the bulb and how it connects to the ground or return path. If that was bad, neither would work. BUT the brake lights work so the ground is PROBABLY ok since the brake light ground is also the tail light ground.

Check to see if there is power getting to the bulb first via John's and my suggestions. Then we'll worry about the rest. The tag light bulb only has one element (and contact), the "running" or tail light bulb has those 2. That's why I'm having you test the end of the pipe at the tag light socket, not in a tail light socket. That way there is no way you can get a false reading from the brake light contact. It's either there or it isn't. If not, you need to go find out why not.

Happy hunting. Let us know what you find. Like I said, we'll get there.
 
1 - 20 of 24 Posts
Top