Brake Light Problems

[Boone83K10]

Been a while since I have been on here. New house and newborn so...

Since we moved to our new house, I haven't messed with the truck. We are about 800 feet higher now and so I decided to just tune the carb some today.

I got that done and noticed that when I hit the brakes my back up lights come on. When I do the left turn signal both the left tail and B/U lights blink. If I signal right it works normally. If I put on the hazards, it makes both B/U and tails come on.

Any idea on where to start?

 

[foamypirate]

Check your grounds, first thing. There should be one that goes to the bed near one of the rear tail lights somewhere.

 

[Boone83K10]

thanks, I should have known.. will look at that tomorrow.

 

[Boone83K10]

I cleaned the ground on the passenger side. still doing the same thing. I noticed that the running light will blink and nothing else if the ground is disconnected behind the driver tail. there must me a ground somewhere else that is crossing over in the wires. therd is a big cluster f#ck ball of wires where someone hacked in a trailer wire hookup.

 

[chengny]

Check that the sockets are clean.

More importantly be sure that each socket has the correct bulb installed - and that they are installed correctly.

It is not unusual for someone to jam a lamp with the wrong base configuration into a socket.

When that happens one lighting circuit bleeds over into another - this most commonly occurs in the middle (brake light/directional) assembly.

When the brakes are applied for example, power is properly supplied to the brake filament post but if a single post bulb is in there it can short over to the other circuits.

Grounding issues generally have more to do with lamps failing to illuminate, slow directionals, dim bulbs, etc.

In situations where bulbs light up without power being supplied to it's associated circuit the cause is almost always a short.

If the harness is as messed up as you say, the short may be occurring in the wiring. But for that to happen the insulation would need to have failed on 2 adjacent wires - and the copper would have to be touching.

The wiring diagram for your 83 rear end lighting groups:

 

[Boone83K10]

on that diagram, the PO tapped into the wiring after the 4 prong plug that goes to the driver tail light. I won't ever use it so I am going to try and undo it all. I hope that is where the foul up is. Doesn't explain why the passenger B/U light illuminates when the left turn signal is put on.

Do you think it could be in the headlight switch or inside the column??? Hope not.

 

[SlickGTP]

One thing to keep in mind is that the tail light harness grounds to the bed, but the bed also has to be grounded to the frame. I had all sorts of crazy light problems when the bed wasn't bolted to the frame solidly.

 

[ScottyB]

on that diagram, the PO tapped into the wiring after the 4 prong plug that goes to the driver tail light. I won't ever use it so I am going to try and undo it all. I hope that is where the foul up is. Doesn't explain why the passenger B/U light illuminates when the left turn signal is put on.

It sure could explain it. If that splice was not done properly then the wiring from all three sides of the splice could start to corrode. You get to a certain point and it isn't any different from losing the circuit at the socket or the switch. Meatball surgery on wiring is a terrible thing and practitioners of this undiscipline ought to be drawn and quartered.

 

[chengny]

Doesn't explain why the passenger B/U light illuminates when the left turn signal is put on.


Do both the left blinker and B/U light illuminate when the left turn is selected (is it only the LH back-up or both sides)?

Does the B/U light(s) flash in synch with the directional - or does it come on and stay steady?

Is the flash rate the same as the R/H side?


The B/U lamps are supplied from the neutral safety switch on the column and then all the way back via the light green wire. That circuit is essentially segregated from the other 2 circuits (parking/marker & brake lights).

If you want to check for shorts in the light switch/steering column area, pull the connector off the neutral safety switch and the B/U's should become non-functional.

If you still get a cross-feed from the turns to the B/U's (with the plug pulled from the NSS) then the short is in the rear wiring harness. Almost certainly downstream from the 4 prong plugs.

 

[Boone83K10]

Left signal: the driver tail and both (driver/passenger) B/U lights illuminate at exactly the same time.

Right signal: works as normal

apply brakes: both tail lights and both B/U lights illuminate at same time and remain on until you take foot off brake.

hazards: both tail lights and B/U lights illuminate together


everything is normal on the front.

 

[Boone83K10]

I got to looking under the truck last night.

There are several two wire splice taps. It looks like the wire splice taps have corroded as well. Hell the brown wire for power to the only one license plate lamp, (it's missing the 2nd one) is just twisted together. I don't know whether to be mad or sad at whomever did this trailer wiring.

My plan is to eliminate the two wire taps and solder the yellow, lt green and dk green wires back together. Then convert the brown license lamps to insulated male/female spades for ease of swap when they go out.

 

[chengny]

Don't forget to put the heatshrink tubing on before making the solder connections.

That's more of a reminder to me than you - if I had a nickel for every time I've finished a soldering job and then realized I forgot to slip the HST on first...

 

[Boone83K10]

chengny

what did you make of how each bulb reacts in my previous post.

 

[chengny]

At first I thought maybe the 4-prong on the LH side was plugged in wrong. But that wouldn't matter - all the circuits are seperate. So shifting the plug would only make the wrong lamps light up, not cause cross-lighting.

If the original wiring is intact (other than the spliced-in trailer lighting harness) I would surgically remove the trailer light kit.

Here's my best guess - in the trailer harness (or where he spliced into the main harness) - I bet the PO spliced the LH blinkers, brakes & B/U's together.

This is because:

1. The B/U's are common to boths sides

2. So are the directionals - but only when powered by the hazard flasher

That would explain these two:

Left signal: the driver tail and both (driver/passenger) B/U lights illuminate at exactly the same time.

hazards: both tail lights and B/U lights illuminate together

When the brakes are applied, power goes everywhere.

 

[Boone83K10]

they didn't do this before when I drove it a lot, which is why it's so weird that it just popped up all the sudden.


edit: I see what you mean now, that it is shorting in the trailer harness itself, not the original wiring.