How I hate electrical issues...

[dvdswan]

So last night verifying the truck would be safe for the road, I had my son help me with the lights. I had brake lights only. No headlights, turn signals, or running lights. Trailer light didn't come on either when the brake lights came on. (Its one of those slide in the receiver hitch lights). As I head back into the garage to get my glasses and flashlight, my son being the wise crack that he is, don't know where he got it from, says, "maybe its a fuse". "You think!?" sure enough fuse was blown.

Good: I have all lights now.
Bad: When the lights are on, tail lamps and trailer light are on as if hitting the brake pedal.

Now, being this is a 40 yo truck and I would hope the low number of previous owners the truck had, one of them was not the sharpest tack in the bunch when it came to wiring. Its pretty ugly under the dash, engine compartment, and chassis. I've pulled out quite a bit of useless wires.

I'm pretty confident the problem/short is in the tail light harness or trailer harness. I just hate going through other peoples work because you never know what you will run into.

So I'm torn between tracking down the short or replacing the harness.

I'm thinking of just buying a length of trailer 4-wire to replace the rear harness as someone had hacked into it years ago.

Any thoughts? Or stories to share of electrical woes...

 

[Honky Kong jr]

Grounds, grounds, grounds add some, it can’t hurt and will be well worth the effort.

 

[hatzie]

There literally are only four wires in the tail harness. Add an additional three for breakaway battery charge power, Ground, and the Electric brake actuator wire and you get the standard seven terminal trailer plug.

I usually find that U-haul or a PO has knackered the tail harness on cars and trucks that are capable of towing anything with the assistance of Scotchlok taps. Scotchloks are an invention of Old Scratch himself to torture people that fix vehicle wiring.

If the molded round plug wiring on the truck is knackered I usually upgrade to the 2x2 4 position Weatherpak. PDFs of the GM factory wiring diagrams with the pinouts, wire-gauge, and connector part numbers are in the Forum library. Mouser Electronics sells the Weatherpak parts and tooling. You can find em on Amazon and The Electrical Depot as well.

Hopkins, Tekonsha, and Curt make a Tee for the 67-82ish round molded plugs and the 83ish-91 Weatherpak plugs with four wires and a Ground to hook to the frame. Plug it in, add the wires to the trailer socket, and go. They make em for a lot of other vehicles too. Chopping up the wiring is completely unnecessary. These have been available since the 1970's but slicing and dicing the wiring was cheaper and it lasts at least a year... Scotchloks are cheaper to stock too.
https://www.etrailer.com/vehicle-finder.aspx?HHcat=t1&HHyear=1978&HHmake=Chevrolet

If the trailer socket has side screw terminals I usually tin the tips of the stranded wires with 60:40 electronics solder and add some grease to each socket. You can use copper thimbles if solder isn't your bag. I usually grease the connectors as well.

This page has the industry standard trailer plug and socket wiring pinouts along with industry standard wiring colors.
https://www.etrailer.com/faq-wiring.aspx

 

[chengny]

So last night verifying the truck would be safe for the road, I had my son help me with the lights. I had brake lights only. No headlights, turn signals, or running lights. Trailer light didn't come on either when the brake lights came on. (Its one of those slide in the receiver hitch lights). As I head back into the garage to get my glasses and flashlight, my son being the wise crack that he is, don't know where he got it from, says, "maybe its a fuse". "You think!?" sure enough fuse was blown.

Good: I have all lights now.
Bad: When the lights are on, tail lamps and trailer light are on as if hitting the brake pedal.

Now, being this is a 40 yo truck and I would hope the low number of previous owners the truck had, one of them was not the sharpest tack in the bunch when it came to wiring. Its pretty ugly under the dash, engine compartment, and chassis. I've pulled out quite a bit of useless wires.

I'm pretty confident the problem/short is in the tail light harness or trailer harness. I just hate going through other peoples work because you never know what you will run into.

So I'm torn between tracking down the short or replacing the harness.

I'm thinking of just buying a length of trailer 4-wire to replace the rear harness as someone had hacked into it years ago.

Any thoughts? Or stories to share of electrical woes...

If you don't mind; I was wondering which fuse was it that you found to be blown?

Reason I ask is because power to the headlights is unfused and independent of all other lighting feeds. The headlight circuit is protected only by a pair of fusible links - located in the engine compartment. The other lighting circuits you mention - as having gone out - branch off before the ignition switched power and are fused. But the lead supplying the headlight terminal (#2) on the H/L switch, by-passes the fuse block entirely and runs straight to the switch.

 

[dvdswan]

Well, the fuse was for the park and turn signal. I check the wiring to the head lights to the firewall and they looked in good shape, I didn't look to hard under the dash just the fuse block area. I'm wondering if the switch may be going south. The rear light harness I found a splice of the 4 wires, ugly butt connectors and they look corroded so that may be the culprit. I'll know more tomorrow and look under the dash as well.

 

[PrairieDrifter]

SCOTCHLOCKS ARE THE DEVIL. They’re a farmers classic go to for electrical fixes lol. I would just take a peek at your headlight switch to see if it’s all melted along with the pigtail for it.

For it acting like your brake lights are always on, look at your brake light switch up under the dash to see if it’s adjusted correctly to the pedal. It could have got bumped or the pedal could be sagging slightly.

 

[T-ROD]

I do believe that it is connected to and from headlight switch with with almost two entirely different circuits (with exception of main source), the headlights are directly wired to high beam switch from headlight switch, and from there going in reverse, there's only a fusible link to that portion of the switch, althoughthe the switch does have a circuit breaker built into the bottom of it, they only wire the parking lights (tail and license), and the dash like this are through the same circuit just through a dimmer inside switch, the parking lamps should never share turn/brake/interior/hazard, or any other circuit, they usually do that setup because starting from the headlamps being most important, a circuit breaker will reset if intermittent short occurs, and fusible link if all else fails can hold Tens of amps for long periods of time before completely giving way, makes them more reliable, second chance to pull over or get it somewhere safely, the brake lamps I believe are wired with 20 Amp AGC if glass 20 Amp ATC if blade fuse, I'd start at the brake lamp switch, but if they are only on when parking lamps are on chances are if the rest aren't working, they are finding path to ground elsewhere into brake lamp circuit, if that's the case though, when you hit the brakes, they should all go off if parking lamp switch is on, if your getting power to the light switch I'd probably forget about the problem being in the cab, it's 99.5% of the time OK beyond there unless someone has hacked in a nice pile of crap there also, but check the fusible links, there is a few, two on starter, one on firewall, just tug a couple times lightly, they shouldn't stretch, and it would be obvious if they are melted I'm sure, and then check for power at the blown fuse you found, if it's all good, it's probably either the firewall connection block, or its a ground problem, although sometimes loads being placed on a circuit could open another circuit elsewhere it's very unlikely, it's probably in those places unless someone done some serious rewiring and Joe knows done blowed his knowledge on it, I'd look there, years with these trucks thought we well in these areas, not to say it is, I've seen weirder things, but I'd start there.

 

[chengny]

Well, the fuse was for the park and turn signal. I check the wiring to the head lights to the firewall and they looked in good shape, I didn't look to hard under the dash just the fuse block area. I'm wondering if the switch may be going south. The rear light harness I found a splice of the 4 wires, ugly butt connectors and they look corroded so that may be the culprit. I'll know more tomorrow and look under the dash as well.

That's where I was headed.

 

[75gmck25]

A few simple checks for light grounds.
- Instrument panel ground is up under the dash. On my older truck its grounded to the emergency brake pedal bracket, but on newer trucks they apparently added a grounding block. If this ground is missing it will cause instrument panel lights and turn signal indicator issues.

- Back up under the bumper, in the middle of the truck, there is a large gauge white harness ground wire that needs to have a good ground to the frame.

- On each side of the radiator support near the headlights there is a black ground wire. The one on the passenger side usually also connects directly to the battery negative.

- If the rear tail-light harness is screwed up badly you can unplug the connector (same place you add a T for trailer lights), and just replace the tail-light harness only.

- If you have issues with individual lights, its usually the ground wire at the light housing, or one of the bulbs is inserted incorrectly/incompletely. These grounds are exposed to water/dirt on the road, so they do deteriorate. There is an electrical cleaning product called DeOxIt that works fairly well to remove oxidation on the inside of the bulb sockets. They used to sell it at Radio Shack, but you might have to go to Amazon to find it these days.

- There should also be braided ground wires from the engine block to the frame and from the passenger side of the block to the firewall. However, if these are missing it usually causes more than lighting problems.


Bruce

 

[dvdswan]

Thank you for the info gentlemen.

 

[dvdswan]

Well, everything is working now. I removed butt connectors from 5 different spots on the harness, removed 3 wires that weren't connected to anything. Cleaned the grounds and secured them. A lot of hack work was done to the truck from prior owners and trailer shop. None of the connectors were taped up so I'm sure corrosion was part of the issue.

 

[roundhouse]

If you have wiring issues and there are butt connectors in sight , that’s usually the problem

Residential wire nuts are better than butt connectors

A good twist and tape is better than a butt connector

Glad you got it fixed

Now get some chrome spray paint to spray the inside of the tail light housing and some LED bulbs and make em twice as bright

 

[smoothandlow84]

If you have wiring issues and there are butt connectors in sight , that’s usually the problem

Residential wire nuts are better than butt connectors

A good twist and tape is better than a butt connector

Glad you got it fixed

Now get some chrome spray paint to spray the inside of the tail light housing and some LED bulbs and make em twice as bright

Household wire nuts need to stay in household wiring...PERIOD...thats what they are designed for...solid copper wiring.


Get rid of all the wiring that has multiple connectors or splice connectors. The more connections the circuit has, the more chances of current loss. Wiring is sold by the foot, just buy and install the correct length for each circuit. If you do need to use or splice into a circuit, then splice connectors if used correctly and sparingly are ok.

Using anti corrosion electrical contact grease with splice connectors and heat shrink is the best if soldering isn't an option.


Sorry guys...but using wire nuts is just plain stupid in any vehicle.

Twist and tape is okay, however, twist, solder and heat shrink tubing is far superior. Too many people don't even use electrical tape for electrical connections in this world. Fwiw...masking and duct tape...don't even think about it as they are not ul listed.


butt connectors are more secure than twist and tape and do serve a purpose. Heat shrink tubing should also be used to seal all butt splice connectors, especially in wet environments.


It should be no suprise that there are still some retards out there using solid copper wiring in auto wiring circuits.

If all else fails and you dont want to use correct wiring techniques and materials, then invest in a high quality fire extinguisher and always carry your cell phone. When your vehicle ignites at least you can keep the fire under control while on the phone calling 911.

 

[dvdswan]

I soldered and used heat shrink on them. I used to build connectors for electronic equipment on ships so no worries there. It's just scary to think what people think is ok to do to even just get them by. But since we are only human we are all guilty in some fashion of that.

 

[henrym]

So last night verifying the truck would be safe for the road, I had my son help me with the lights. I had brake lights only. No headlights, turn signals, or running lights. Trailer light didn't come on either when the brake lights came on. (Its one of those slide in the receiver hitch lights). As I head back into the garage to get my glasses and flashlight, my son being the wise crack that he is, don't know where he got it from, says, "maybe its a fuse". "You think!?" sure enough fuse was blown.

Good: I have all lights now.
Bad: When the lights are on, tail lamps and trailer light are on as if hitting the brake pedal.

Now, being this is a 40 yo truck and I would hope the low number of previous owners the truck had, one of them was not the sharpest tack in the bunch when it came to wiring. Its pretty ugly under the dash, engine compartment, and chassis. I've pulled out quite a bit of useless wires.

I'm pretty confident the problem/short is in the tail light harness or trailer harness. I just hate going through other peoples work because you never know what you will run into.

So I'm torn between tracking down the short or replacing the harness.

I'm thinking of just buying a length of trailer 4-wire to replace the rear harness as someone had hacked into it years ago.

Any thoughts? Or stories to share of electrical woes...

I totally understand about hating electrical, regarding the harness running to the rear, I did exactly that, except I used a 7 wire trailer harness, so i had an extra wire for my electric trailer brake, and for a rear mount light that I use with a toggle for extra lighting while backing up in sketchy territory, or hooking up said trailer. Works like a charm, and no extra wiring needed.