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Old 01-12-2010, 12:13 AM
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re-wiring c1500

To start off, I have a 91 c1500. I replaced the stock TBI 350 with a carbureted 355 so I have a lot of wires that originally went to the TBI set-up that are not in use anymore. Also I have electrical issues with blinkers, fuel system, and a couple interior lights. I want to get aftermarket electric gauges as well. So I've decided I'm going to take out all of the old wiring and computer and replace it with a new wiring harness and new gauges, so everything will be new and problem free.
As far as wiring experience goes I have only done small things like a CD player with speakers/subs, a tach, and various other small projects like those. I do realize this is not a small project and it will take time. This is fine because it is not my daily driver and will not matter if its out of service for a while.
I know there is quite a few different brands out there that make harnesses, but what I don't know is which brand would be the easiest, or if there even is an "easiest" brand. I'd also like to know if these kits come with absolutely everything I'll need or if there will be other stuff needed.


Thanks for any feedback...Andy

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Old 01-12-2010, 08:00 AM
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I believe your 91 if it has an automatic transmission has an electronic speedo that feeds into the computer. Also the anti lock brake system feeds into and is activated by the computer. You had better think this out a little further before ripping everything out. Depending on where you live you may not be able to get the truck inspected if you rip out the computer.


Vince
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Old 01-12-2010, 09:37 AM
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Quote:
Originally Posted by 302 Z28
I believe your 91 if it has an automatic transmission has an electronic speedo that feeds into the computer. Also the anti lock brake system feeds into and is activated by the computer. You had better think this out a little further before ripping everything out. Depending on where you live you may not be able to get the truck inspected if you rip out the computer.


Vince




Thanks for pointing that out. As far as the transmission goes, yes, its a 700r4; however I believe there is a trans controller I can buy so that the 700 will work with a carbureted engine. Also I don't know how its hooked up exactly, but as of right now its working with the engine somehow. Now the ABS I have not though about, nor do I know how to go about that problem.
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Old 01-12-2010, 09:47 AM
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Andy,
your ride has so many special termination connectors designs it's not likely available in the general aftermarket....

you can contact some local body shops to see what harnesses are available for collision repairs (and gasp when the tell you the price!)

it's not rocket science to trouble shoot / diagnos and correct the very very common problems you listed....

on this link, scroll down and read the "electrical trouble shooting" article(s)

http://www.aa1car.com/carleyware/library.htm

it is just a step by step testing and eliminating procedure starting from one end or the other of any problem curcuit to pin down the problem souce...

in a sense it is the same as Sherlock Holmes solving a murder for (in this case) "what" is the guilty party...

I prefer and use a volt meter for everything but for very many common problems just a cheap probe test lamp is all you do need...

suggestion,,,keep this "picture" in your head:
on a car 12V neg ground system,,,, the energy flow is from the neg batt terminal thru the car body (electrical conductor) and ground wire at the device where "work" is done by the device with on/off control from a switch and what energy is left after the work is sucked to the positive terminal...
that explains why you disconnect the neg batt cable to work on the electrics in a car to truly kill the "energy source" (and why by far lost ground curcuit side energy "supply" is the most common problem source)...
so most often I do start troubleshooting from the "supply" end of the curcuit...

it is SO worthwhile to learn how to do the troubleshooting basics because it is the same procedure for correcting anything electrical in your life.... (appliance/outboard/house/whatever)
to save service call bucks for the rest of your life....

Last edited by red65mustang; 01-12-2010 at 09:57 AM.
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Old 01-12-2010, 10:21 AM
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ok thanks, I'll definitely read into that. I realize that finding a kit like mine is not likely, unless i did what you said and called a body shop or junk yard to get a replacement, but thats the thing, I don't want a replacement. I would like to set this up as if it was an older vehicle without a computer, and so I can get some aftermarket gauges. I know it probably would not be to hard to track down these common problems, but there is also a lot of wires that have been messed with, along with a lot of wires that are not in use anymore as I've already stated. I'm basically redoing the whole truck and figured if I fixed those problems, who's to say there wont be more electrical issues later? I just thought it might be better to start over new. Maybe not?...I'm not trying to argue, I'm just trying to figure out what's best. I'm making everything else new so why not that?

Thanks again for the replies.
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Old 01-12-2010, 11:00 AM
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Painless makes a harness for 1973-'87 Chevy trucks that might fit the bill, P/N 10205.

They have a 12 circuit pick up harness w/GM column, P/N 10103.

They also make a 'universal' 12 or 18 circuit street rod-type harness for a GM column that could be adapted. P/N 10101/10201.
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Old 01-12-2010, 11:40 AM
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honestly,
there is no real big difference between a carb or TBI functionally...
(one sucks fuel the other squirts fuel)

there is a HUGE difference and advantage when you can simply plug in a diagnostic scanner to tell you exactly what a problem is on a stock harness!!!

I picked this (nightmare) thread example at random just to give you a "clue" for what it takes to just get a tranny shift controller to work....

http://www.fullsizechevy.com/forums/...00r4-swap.html

the smart plan is put the tbi back on the motor and hook up all the wiring factory correct....
(or take all the courses needed to truly understand what you are doing)

enough time and $$$$ you can do anything but the actual results will be not as good as when you started (and endless hours of trouble shooting debug and tuning to gain nothing)....

actually read the instructions first when swapping or adding guages does make that job relatively simple

Last edited by red65mustang; 01-12-2010 at 11:53 AM.
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Old 01-12-2010, 01:22 PM
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I did this exact thing on my '91 truck, so I know what problems you are facing.

First of all, the transmission is not electronically controlled, so the only thing the computer is used for is torque converter lockup. You will need to buy a lock up kit to control this.

The ECM is also not used for any of the gauges in your truck. They will all work perfectly provided they work now and you have all of the sensors (oil, water, fuel) installed. The idiot lights also work, except for the check engine light (obviously).

I removed the whole harness and basically disassembled it and removed the wires that I did not need (injectors, TPS, MAP, etc.). It's not very difficult to do this right, just start at the inside and remove the ECM, and untape the harness so you can see that nothing is holding it in the truck anymore. Then unscrew the grommet that holds the hole thing in the vehicle from under the hood and pull it out. I used wire diagrams that listed what each wire did to decipher what I still needed, and in the end, it wasn't much. In the end, both connectors that went to the ECM were no longer needed.

You're problem's sound like they may be ground related, and this will not fix those problems. Get some wire diagrams and start tracing down the grounds. I honestly wouldn't waste the time or money in a new harness.

What specifically is going on with your electrical problems? What happens with the blinkers, fuel system, etc?

TBI is nice if it's your daily driver and having a carb on a TBI vehicle is illegal. I tried tuning my TBI for years and spent thousands of bucks trying to make it run good. I finally threw in the towel when I couldn't tune it enough to make it pass emissions. I installed a carb setup and it now passes emissions with flying colors and also hauls ***.
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Old 01-12-2010, 01:46 PM
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Quote:
Originally Posted by red65mustang
honestly,
there is no real big difference between a carb or TBI functionally...
(one sucks fuel the other squirts fuel)

there is a HUGE difference and advantage when you can simply plug in a diagnostic scanner to tell you exactly what a problem is on a stock harness!!!

I picked this (nightmare) thread example at random just to give you a "clue" for what it takes to just get a tranny shift controller to work....

http://www.fullsizechevy.com/forums/...00r4-swap.html

the smart plan is put the tbi back on the motor and hook up all the wiring factory correct....
(or take all the courses needed to truly understand what you are doing)

enough time and $$$$ you can do anything but the actual results will be not as good as when you started (and endless hours of trouble shooting debug and tuning to gain nothing)....

actually read the instructions first when swapping or adding guages does make that job relatively simple


Well I'm keeping this motor, I'm not changing back. That guy had a different tranny than I did as well. I don't want a stock truck or I would have kept that motor. Maybe its not the smartest route to go but I can't just get rid of my motor, I just had it built the way I wanted it.
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Old 01-12-2010, 01:59 PM
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Quote:
Originally Posted by Pre-Tuner
I did this exact thing on my '91 truck, so I know what problems you are facing.

First of all, the transmission is not electronically controlled, so the only thing the computer is used for is torque converter lockup. You will need to buy a lock up kit to control this.

The ECM is also not used for any of the gauges in your truck. They will all work perfectly provided they work now and you have all of the sensors (oil, water, fuel) installed. The idiot lights also work, except for the check engine light (obviously).

I removed the whole harness and basically disassembled it and removed the wires that I did not need (injectors, TPS, MAP, etc.). It's not very difficult to do this right, just start at the inside and remove the ECM, and untape the harness so you can see that nothing is holding it in the truck anymore. Then unscrew the grommet that holds the hole thing in the vehicle from under the hood and pull it out. I used wire diagrams that listed what each wire did to decipher what I still needed, and in the end, it wasn't much. In the end, both connectors that went to the ECM were no longer needed.

You're problem's sound like they may be ground related, and this will not fix those problems. Get some wire diagrams and start tracing down the grounds. I honestly wouldn't waste the time or money in a new harness.

What specifically is going on with your electrical problems? What happens with the blinkers, fuel system, etc?

TBI is nice if it's your daily driver and having a carb on a TBI vehicle is illegal. I tried tuning my TBI for years and spent thousands of bucks trying to make it run good. I finally threw in the towel when I couldn't tune it enough to make it pass emissions. I installed a carb setup and it now passes emissions with flying colors and also hauls ***.

Awesome, good to know there's someone that has gone through this before. I've had a carbed engine in there for a couple years now, but just had a different one built for more power. The blinker problems I've had for a year or so, the fuel problem is new. The blinkers will work for 2 seconds or even 2 hours, then it blows a fuse. The fuel system problem is that the fuel pump is not turning on. A guy I know intsalled a jumper wire in a little plug connecter thing under the hood by the a/c that makes the fuel pump turn on; however the fuel pump stays on at all times. It never shuts off unless I pull the jumper wire out. I didn't know the gauges would still work, thats good, but i would still like to get aftermarket gauges...is that possible? And yes I too love the carbed engine, it really moves
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Old 01-12-2010, 02:47 PM
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I mis-read your post,,,I thought you still had the tbi unit and tbi intake available

learn just the basics of electrical troubleshooting and you can correctly fix your problems....
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Old 01-12-2010, 03:02 PM
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Quote:
Originally Posted by red65mustang
I mis-read your post,,,I thought you still had the tbi unit and tbi intake available

learn just the basics of electrical troubleshooting and you can correctly fix your problems....

Oh ok I see, not a problem, and I'll work on that, thanks
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Old 01-12-2010, 03:34 PM
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Also, anyone know where to get any wiring diagrams??? Would a Haynes book(think thats what its called) have one?...Thanks
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Old 01-12-2010, 03:43 PM
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Quote:
Originally Posted by lowandloud91
Also, anyone know where to get any wiring diagrams??? Would a Haynes book(think thats what its called) have one?...Thanks
Haynes maybe, Chilton prob. not, Motors prob. not, unless they're the pro series.

Factory will, but you will have to get the right one (there are Overhaul Manuals, Repair Manuals, etc.), and they're high priced- but good.
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Old 01-12-2010, 03:52 PM
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Quote:
Originally Posted by cobalt327
Haynes maybe, Chilton prob. not, Motors prob. not, unless they're the pro series.

Factory will, but you will have to get the right one (there are Overhaul Manuals, Repair Manuals, etc.), and they're high priced- but good.
Ok, I'll look into a Haynes. Can I go to a GM dealer to get a factory manual?
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