Rear tail lights.... Some work but not always?

[K10mashup350]

So I just replaced me taillight harness from fuse panel all the way back to the lights (including the "t" for the actual lights) so "technically" 2 harnesses. The reason was when I bought this truck they had every wire harness cut an hacked an almost nothing worked an the taillight harnesses weren't even there....
But my issue is that they don't work running lights work always, and sometimes(not often at all) the break and hazard (not signal) will work drivers side only and nothing on pass side. Fuses look good an flasher seems to work as the front works....

More about the harnesses I put in:
They were not new or 100% intact, I did have to "reconnect" a few locations/light sockets and I did so with heat shrink then fully wrapped the harnesses with wire loom and electrical tape to ensure no wires can come in contact with anything an "rub" to where there could be a short in the lines...
As I had all the wires "bare" I inspected them for cracks/imperfections and corrected the few that I did find, so in all aspect the harnesses are now "new" without defects.... But I still don't have working taillights....

Any help on this would be greatly appreciated so that I can drive my truck, an be able to get my certification...

Thanks

[rich weyand]

OK, so you have all the "+" connections taken care of, but did you check the "-" connections? 

There should be a ground strap (copper braid) from the driver's side head of the block (where most people have the power steering pump bracket connected) to the top of the frame rail near the steering box.  Is that ground in place?

There should also be a sheet metal ground from the light basket to the body work on the driver's side tail lights, and, on some years, the same thing on the passenger's side.  Are those grounds in place?

The grounds need to be clean and tight.  Sometimes oxidation gets in between the connector and the surface, so you have to take them off and clean them and mount them back tight.

The issue is that, due to the insulating engine mounts and the insulating cab bushings, the engine, cab, and frame are not electrically connected without the ground braids.  (The one from the engine to the cab comes off the rear of the passenger side head to the firewall.)  To connect four devices electrically (batter, engine, fram, and cab) takes three wires.  Everyone has the connection from the battery to the alternators bracket, but the other two straps from the heads to the firewall and the frame rail are often missing.

[K10mashup350]

Ok I'm missing those "extra" grounds, I have the one behind driver taillight an one after license plate light, but I don't have the cab to frame, or engine to frame grounds I guess there missing I see the connector for where the can to frame(on cab) ground used to be but the wire is missing

[rich weyand]

The originals were braided copper straps, but you can use 12 AWG stranded wire with 3/8" eye terminals.

1) firewall (on the flat close to the beginning of the arch of the hump indent) to the 3/8-16 hole on the back side of the head, or to the outside rear valve cover screw.

2) driver's side head at the power steering pump bracket to the top of the frame rail just behind the steering box.

Without these, nothing in the cab or on the frame or body will work reliably.

Here's the passenger side one:

[Irish_Alley]

grounds arent a bad thing but just so you know, rich's might have one on his power steering pump, but i dont have one on any of my trucks (75,79,84,86 or 96) nor have a seen one. so if you adding grounds add it, but you will manage without.

[rich weyand]

Well, he can test it simply enough by connecting ANY engine bolt to ANY place on the frame -- temporarily, even with a starter cable -- and see if that clears up his tail lights problem.

[rich weyand]

Better pics.

Engine to firewall:


Engine to frame rail:

[rich weyand]

bd reminds me in private message that better than the valve cover bolt is to use the 3/8-16 threaded hole on the back side of the head, which is the twin to the one on the other side head where the frame rail strap connects.  Better long-term electrical contact.

And I agree with him.  I am aware of the issue, and keep an eye on it, but I should have mentioned that the valve cover bolt is second-best to connecting it to the head.

[hatzie]

I ran braided grounding straps from the block to the frame along the motor mounts and from the threaded hole in the back of the RH head to the firewall. I figure it's a bit more protected there.

From orbit via Android.

[K10mashup350]

So I've put in grounds all over the place, cab to batt, engine to frame, engine to batt, cab to engine.... An still have the same issue, only thing I haven't done is run a temp line from batt to rear sheet metal ground behind light to double check that

[Irish_Alley]

Did you clean the grounds on the rear? If you have a test light test for power at the "t" and trailer harness

[K10mashup350]

No I don't have a test light (lost it a while back an haven't replaced it yet) but I do have a volt meter that I know where it is

[K10mashup350]

So I still have no clue as to what the heck is going on with this... Tried a new plug(just incase) grounded everything I could thing of to the frame/battery, I even ran temp ground from battery to "sheet metal" ground behind light an still nothing? If I put my volt meter to the "T" plug I can get a reading, but it's very low... Nowhere near 13v..... Any more ideas?

[bake315]

You might try jiggling the half of the plug that connects directly to the back of the fuse block (the one that has all the lighting circuits in it), to see if there is any improvement.  Also, make sure the bolt that holds both halves is snug.  I noticed a similar occurrence when dealing with a separate issue, and had it apart.

[Dan75k20]

I agree with bake i had the same problem and i disconnected the wires from fuseblock on firewall plugged it back in , you have to make sure it is completely seated