Wiring issues

[docstoy]

Ok,here we go. After inspecting your grounds for being clean and tight, turn key on, do you here fuel pump run for a few seconds,if yes next,if no ck fuse for fuel pump , your ses light on key on engine off and not trying to crank, if yes good if no inspect fuses, do you have owners manual for your truck ? If you do then it will show locations of fuses. If not I'll try to tell which ones you need to ck/inspect. They will be underhood left side behind pcm/vcm and at left side of dash. Let's get that far first as I suspect you may have blown a fuse when you saw sparks. You need to ck underhood fuses ecm-b, ecm-1 , eng-1 , ign-e , ign-a , ign-b , these are to get it to run and not all that are needed to drive . Left dash fuse block fuse #1, #4 , #14 , #18 , #20 , #24 . I think that's all for powertrain operation and dash operation also your fuse panel covers may still have a picture of fuse location/description . If you had fuse(s)blown and you replaced them. Cycle key to prime fuel system and see if it will crank and start if not we will continue. You will need fuel pressure gage and spark tester .

 

[docstoy]

Grounds that I'm aware of ,behind your battery at fender, ground under heater hoses to frame , ground at thermostat housing /upper radiator hose , you need to remove battery to ck first one and while you have battery off ck power wire on back side of underhood fuse block probably not all but should be enough to run. Also when reconnecting battery positive cables first with cable that runs across radiator /upper fan shroud next to battery then spacer then rear positive cable , then connect negative cable, again , cables , spacer should be free of corrosion . Hope this helps

 

[Road Trip]

Hey guys, I’m struggling to get my truck running. I don’t even know where to begin… sigh



To start with, it’s an electrical issue & it’s been plaguing my truck for abt 2 years now & only getting worse. Right now I can’t even get it to run, just crank. When I turn my brights on, the windshield wipers go on too, full speed. While this is happening, the driver side high beam is completely dead.

So I replaced both the windshield wiper motor & the headlight harness & neither fixed the issue. The high beam bulb is good I can get it to come on if I give it direct power.

I did the trick with the test light where you bridge the neg cable & the neg post on the battery to see if you got a short & it lit up. Then I went to the fuse box & started pulling fuses one by one & when I remove the BAT fuse, light goes out.



Ok where getting somewhere… except now idk what to do.


I’ve replaced the fuse box already bc it had some bad looking burns on the bottom side. I’m 100% positive I did that correctly bc I took pics & moved wires over one at a time using a q tip to keep myself from forgetting which slot it came out of from the old one. & I even got the truck to start once after I was finished. But then I went to put it back onto the little plastic stand & something arced & the truck died again…

Ignition switch also replaced with one from an identical truck. I know that doesn’t mean it was good but it looked a lot better than the one I pulled from my truck did.


Sigh…



Someone pls help me my truck has been down for like a year now.

Greetings MYF,

A saying that I happen to agree with is that you don't fail until you quit. I know what it's like to have a
project get bad stuck, and you start to get the feeling that this is going to become a failure that will color
how you feel about your ability to keep something rolling down the road. :-(

But then I'd finally decide to reach out to a a mentor and ask for help, and to my surprise they would coach
me on the repair until the yard art was transformed back into solid transportation. They would use the broken
machine as a real world training exercise. And when I asked them why they were willing to help me, they
would simply reply that they remembered what it was like to be stuck, and have an elder help them.

So we're here to help. And it's possible to pull this off -- awhile back some guy had been given a GMT400
for free because it had bad electrical problems, but over time we worked through the issues methodically,
and the last we heard from him he was pretty happy with how it turned out...even at night. :0)

****

Enough setting of the dinner table. As long as your truck is wounded but stock, then with the Factory Service Manuals
we *can* get this sorted out. First things first. When you have electrical failures that make sense but can't be fixed by
swapping parts, then it's usually a power problem. But when you have illogical (ie: functionally unrelated) electrical problems,
it is usually traced back to a shared ground. And these can test the patience of even the most seasoned troubleshooter.

So I propose to give you a quick tutorial on how to take weird failure symptoms and locate a shared electrical connection between them.

When I turn my brights on, the windshield wipers go on too, full speed. While this is happening, the driver side high beam is completely dead.

OK. You have a '97, but I've discovered that the '99 FSM (Vol 4, Electrical Wiring section) is pretty much identical,
so I opened up the copy on my laptop and started scanning the ground distribution diagrams looking for anything
shared by the headlight & windshield washer wiper circuit. Check this out:

You must be registered for see images attach

Of course, with nothing more than the symptoms you shared this isn't incontrovertible proof that G200 must be a marginal ground
and is the root cause, but by the same token the headlights and windshield wipers are on separate power fuses and are otherwise functionally
independent. But the control modules for these 2 systems do share the same ground. And when electrical circuits backfeed
through other circuits due to a shared marginal ground you can experience some pretty weird symptoms. As a matter of fact there's
plenty of real world examples illustrating this sprinkled throughout the forum.

Since we now have a troubleshooting interest in G200, is the location of G200 documented in the '99 C/K Electrical Service Manual?

You must be registered for see images attach

In the general area under the steering wheel on the inside of the dash is the physical location of G200.
WITH THE BATTERY DISCONNECTED, remove G200, clean every surface back to shiny metal, and reassemble/secure
this ground. If this solves the interaction issue, great! If not, your time was not wasted, for grounds in new
condition just make all subsequent electrical troubleshooting in the area that much more clear & unambiguous.

Speaking of which, on a truck this old it would well worth inspecting/renewing every ground on the truck. Fortunately,
the General has a short list of every single ground in the wiring harness. (See 1st attachment for the list.)

****

So I replaced both the windshield wiper motor & the headlight harness & neither fixed the issue. The high beam bulb is good I can get it to come on if I give it direct power.

To test the bulb, did you just apply +12V and used the existing ground? Or did you use 2 wires (+12v & ground) in order to test the bulb?
I'm trying to figure out if G113 is a suspect ground or not:

You must be registered for see images attach

By the way, if you would like a brief tour of how the electrical wiring system is laid out in the General's
Factory Service Manuals, then head over hear and give this a read. (Wiring diagram info in the FSM)

Since you haven't been all that active in this forum, I'm going to assume that you are not aware
that thanks to the efforts of others there are the factory service manuals for your vehicle available
for free download over here. If you haven't already done so, give yourself the gift of the best
documentation available to use when troubleshooting/fixing your GMT400.

****

I was going to start in on the spark/no start after issue, but this is already longer than it should be.

If nothing else, from this point forward whenever you are getting ready to move any part of the wiring
harness around (either to Facilitate Other Maintenance or post repair reinstallation) ...never do this with
the battery connected. It's just too easy to have a momentary slip, arc is generated, and suddenly
POOF $$$ go up in smoke. Myself, I learned this the hard way, and in 20/20 hindsight what happened
to me was all too predictable. But at the same time I appreciate your honesty, and between our 2 stories
hopefully others reading this thread while researching similar issues will be able to learn from our
misadventures and avoid doing this to themselves.

We covered a lot of ground, but again as long as you can get the wiring on your truck back to stock
(if any mods have been made) ...then between the all of us we should be able to get your truck
back on the road and once again earning it's keep.

Hope this helps. Best of luck. And let us know what you discover.

Cheers --

 

[Canadian Rust Bucket]

I’ve replaced the fuse box already bc it had some bad looking burns on the bottom side... But then I went to put it back onto the little plastic stand & something arced & the truck died again…

I'm not an incredibly experienced electrical troubleshooter. But I think this is a really good place to start looking. The fuse box is plastic. The stand is plastic. So what could possibly have arced? My vote is you've got a pinched or frayed wire in that area that's causing a short. Maybe something that is connected to the fuse box that only made contact with the body when you lowered the fuse box back into place.

 

[HotWheelsBurban]

Where’d you purchase the disconnect?

Yes I'd like to know too. Thinking about this for my trucks.

 

[Caman96]

Yes I'd like to know too. Thinking about this for my trucks.

I’d post the link, but Amazon links seem hit or miss lately. $12.99

You must be registered for see images attach

It’s made better than it looks in picture.

 

[99xcss4]

Yes I'd like to know too. Thinking about this for my trucks.

that is a good idea here is some https://www.ebay.com/itm/2047708567.../Z3qCAG4RSq7LZFLBIY34FgDs=|tkp:BlBMUJqhmvXvYw https://www.ebay.com/itm/2019861645...wqdjVkdQEO9cpb8iKbDWrunA==|tkp:BlBMUJqhmvXvYw https://www.ebay.com/itm/1343372633...zei+QFos6EKUOmkKPEu2UEbNzQ==|tkp:BFBMmqGa9e9j https://www.ebay.com/itm/4032416079...AWevj4Juwpnpu11yGQPFcCvdkQ==|tkp:BFBMmqGa9e9j

 

[MurderYurFace]

Greetings MYF,

A saying that I happen to agree with is that you don't fail until you quit. I know what it's like to have a
project get bad stuck, and you start to get the feeling that this is going to become a failure that will color
how you feel about your ability to keep something rolling down the road. :-(

But then I'd finally decide to reach out to a a mentor and ask for help, and to my surprise they would coach
me on the repair until the yard art was transformed back into solid transportation. They would use the broken
machine as a real world training exercise. And when I asked them why they were willing to help me, they
would simply reply that they remembered what it was like to be stuck, and have an elder help them.

So we're here to help. And it's possible to pull this off -- awhile back some guy had been given a GMT400
for free because it had bad electrical problems, but over time we worked through the issues methodically,
and the last we heard from him he was pretty happy with how it turned out...even at night. :0)

****

Enough setting of the dinner table. As long as your truck is wounded but stock, then with the Factory Service Manuals
we *can* get this sorted out. First things first. When you have electrical failures that make sense but can't be fixed by
swapping parts, then it's usually a power problem. But when you have illogical (ie: functionally unrelated) electrical problems,
it is usually traced back to a shared ground. And these can test the patience of even the most seasoned troubleshooter.

So I propose to give you a quick tutorial on how to take weird failure symptoms and locate a shared electrical connection between them.




OK. You have a '97, but I've discovered that the '99 FSM (Vol 4, Electrical Wiring section) is pretty much identical,
so I opened up the copy on my laptop and started scanning the ground distribution diagrams looking for anything
shared by the headlight & windshield washer wiper circuit. Check this out:

You must be registered for see images attach

Of course, with nothing more than the symptoms you shared this isn't incontrovertible proof that G200 must be a marginal ground
and is the root cause, but by the same token the headlights and windshield wipers are on separate power fuses and are otherwise functionally
independent. But the control modules for these 2 systems do share the same ground. And when electrical circuits backfeed
through other circuits due to a shared marginal ground you can experience some pretty weird symptoms. As a matter of fact there's
plenty of real world examples illustrating this sprinkled throughout the forum.

Since we now have a troubleshooting interest in G200, is the location of G200 documented in the '99 C/K Electrical Service Manual?

You must be registered for see images attach

In the general area under the steering wheel on the inside of the dash is the physical location of G200.
WITH THE BATTERY DISCONNECTED, remove G200, clean every surface back to shiny metal, and reassemble/secure
this ground. If this solves the interaction issue, great! If not, your time was not wasted, for grounds in new
condition just make all subsequent electrical troubleshooting in the area that much more clear & unambiguous.

Speaking of which, on a truck this old it would well worth inspecting/renewing every ground on the truck. Fortunately,
the General has a short list of every single ground in the wiring harness. (See 1st attachment for the list.)

****



To test the bulb, did you just apply +12V and used the existing ground? Or did you use 2 wires (+12v & ground) in order to test the bulb?
I'm trying to figure out if G113 is a suspect ground or not:

You must be registered for see images attach

By the way, if you would like a brief tour of how the electrical wiring system is laid out in the General's
Factory Service Manuals, then head over hear and give this a read. (Wiring diagram info in the FSM)

Since you haven't been all that active in this forum, I'm going to assume that you are not aware
that thanks to the efforts of others there are the factory service manuals for your vehicle available
for free download over here. If you haven't already done so, give yourself the gift of the best
documentation available to use when troubleshooting/fixing your GMT400.

****

I was going to start in on the spark/no start after issue, but this is already longer than it should be.

If nothing else, from this point forward whenever you are getting ready to move any part of the wiring
harness around (either to Facilitate Other Maintenance or post repair reinstallation) ...never do this with
the battery connected. It's just too easy to have a momentary slip, arc is generated, and suddenly
POOF $$$ go up in smoke. Myself, I learned this the hard way, and in 20/20 hindsight what happened
to me was all too predictable. But at the same time I appreciate your honesty, and between our 2 stories
hopefully others reading this thread while researching similar issues will be able to learn from our
misadventures and avoid doing this to themselves.

We covered a lot of ground, but again as long as you can get the wiring on your truck back to stock
(if any mods have been made) ...then between the all of us we should be able to get your truck
back on the road and once again earning it's keep.

Hope this helps. Best of luck. And let us know what you discover.

Cheers --

You are a godsend! Thank you so much for that thorough explanation. I think I know what I need to do. Will update everyone with the result soon! Again, thank you!

 

[MurderYurFace]

Greetings MYF,

A saying that I happen to agree with is that you don't fail until you quit. I know what it's like to have a
project get bad stuck, and you start to get the feeling that this is going to become a failure that will color
how you feel about your ability to keep something rolling down the road. :-(

But then I'd finally decide to reach out to a a mentor and ask for help, and to my surprise they would coach
me on the repair until the yard art was transformed back into solid transportation. They would use the broken
machine as a real world training exercise. And when I asked them why they were willing to help me, they
would simply reply that they remembered what it was like to be stuck, and have an elder help them.

So we're here to help. And it's possible to pull this off -- awhile back some guy had been given a GMT400
for free because it had bad electrical problems, but over time we worked through the issues methodically,
and the last we heard from him he was pretty happy with how it turned out...even at night. :0)

****

Enough setting of the dinner table. As long as your truck is wounded but stock, then with the Factory Service Manuals
we *can* get this sorted out. First things first. When you have electrical failures that make sense but can't be fixed by
swapping parts, then it's usually a power problem. But when you have illogical (ie: functionally unrelated) electrical problems,
it is usually traced back to a shared ground. And these can test the patience of even the most seasoned troubleshooter.

So I propose to give you a quick tutorial on how to take weird failure symptoms and locate a shared electrical connection between them.




OK. You have a '97, but I've discovered that the '99 FSM (Vol 4, Electrical Wiring section) is pretty much identical,
so I opened up the copy on my laptop and started scanning the ground distribution diagrams looking for anything
shared by the headlight & windshield washer wiper circuit. Check this out:

You must be registered for see images attach

Of course, with nothing more than the symptoms you shared this isn't incontrovertible proof that G200 must be a marginal ground
and is the root cause, but by the same token the headlights and windshield wipers are on separate power fuses and are otherwise functionally
independent. But the control modules for these 2 systems do share the same ground. And when electrical circuits backfeed
through other circuits due to a shared marginal ground you can experience some pretty weird symptoms. As a matter of fact there's
plenty of real world examples illustrating this sprinkled throughout the forum.

Since we now have a troubleshooting interest in G200, is the location of G200 documented in the '99 C/K Electrical Service Manual?

You must be registered for see images attach

In the general area under the steering wheel on the inside of the dash is the physical location of G200.
WITH THE BATTERY DISCONNECTED, remove G200, clean every surface back to shiny metal, and reassemble/secure
this ground. If this solves the interaction issue, great! If not, your time was not wasted, for grounds in new
condition just make all subsequent electrical troubleshooting in the area that much more clear & unambiguous.

Speaking of which, on a truck this old it would well worth inspecting/renewing every ground on the truck. Fortunately,
the General has a short list of every single ground in the wiring harness. (See 1st attachment for the list.)

****



To test the bulb, did you just apply +12V and used the existing ground? Or did you use 2 wires (+12v & ground) in order to test the bulb?
I'm trying to figure out if G113 is a suspect ground or not:

You must be registered for see images attach

By the way, if you would like a brief tour of how the electrical wiring system is laid out in the General's
Factory Service Manuals, then head over hear and give this a read. (Wiring diagram info in the FSM)

Since you haven't been all that active in this forum, I'm going to assume that you are not aware
that thanks to the efforts of others there are the factory service manuals for your vehicle available
for free download over here. If you haven't already done so, give yourself the gift of the best
documentation available to use when troubleshooting/fixing your GMT400.

****

I was going to start in on the spark/no start after issue, but this is already longer than it should be.

If nothing else, from this point forward whenever you are getting ready to move any part of the wiring
harness around (either to Facilitate Other Maintenance or post repair reinstallation) ...never do this with
the battery connected. It's just too easy to have a momentary slip, arc is generated, and suddenly
POOF $$$ go up in smoke. Myself, I learned this the hard way, and in 20/20 hindsight what happened
to me was all too predictable. But at the same time I appreciate your honesty, and between our 2 stories
hopefully others reading this thread while researching similar issues will be able to learn from our
misadventures and avoid doing this to themselves.

We covered a lot of ground, but again as long as you can get the wiring on your truck back to stock
(if any mods have been made) ...then between the all of us we should be able to get your truck
back on the road and once again earning it's keep.

Hope this helps. Best of luck. And let us know what you discover.

Cheers --

Oh sorry, when I tested the driver side high beam bulb for functionality, I removed it from the housing & gave it direct power with some wire & alligator clips to a different 12v battery. I just wanted to verify that it did indeed work

 

[Erik the Awful]

Regarding battery disconnects, I really don't like the exposed blade switches, even if you're putting them on the ground side.

3x the price, but far safer and less prone to corrosion. This one's also rated to carry starting current.

Longacre Push/Twist Battery Disconnect Switch - 2 Terminal - Demon Speed Motorsports

Longacre Push/Twist Battery Disconnect Switch - 2 Terminal - Demon Speed Motorsports

demonspeed.com

If you're expecting to shut off power while the engine's running (emergency shutoff), you'll want a four pole switch so you don't spike the alternator.

JOES Heavy Duty 4 Terminal Battery Disconnect - JOES Racing Products

JOES Heavy Duty 4 Terminal Battery Disconnect Switches are designed for cars that run high amp Alternators and need to isolate the Alternator to a separate

www.joesracing.com