I decided to ditch the “stock” motor that came with my 88 Blazer for a GM Pefromace parts 350 with a Holley 650 carb and HEI distributor. So the wiring harness is pretty hacked up with butt connectors and several “custom” options. So I’m really wondering should I ditch the factory harness and go with a painless set up or should I try to find a factory one and go that route. I would like to keep the stock gauge cluster. If anyone knows where to get a harness that would be a great help. Thanks.
CK5
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TBI to crate 350 (harness question)
- Thread starter Rooneyb
- Start date
I’m doing some work on this now but I’m in the infancy stages and I haven’t stripped anything yet, my plan is to start at the ECM in the glove box by removing it and move forward with pulling the harness through the firewall and out of the engine bay from there, I’ll then figure out what is attached to the TBI harness and work forward from there with reverse engineering. I want to try to find my own key on power for the distributor without having to hack a bunch of the wiring. From what I understand the TBI stuff is fairly stand alone and most of the harness will come out and not need to be cannibalized, I’m posting mostly for thoughts and opinions on this method and to see if anyone tells me I’m not on track and has a better thought process. There isn’t a lot of support from my searches for removing the TBI unless I’m missing something. I also don’t want to hack up my TBI stuff because one day I’d like to use it or sell it and not trash it.
One of my concerns is the fuel pump power, I plan to use the in tank lift pump and I’m only guessing here but I fear that the pump maybe run off the TBI harness. My thoughts are I’ll either give it power (safely of course) or I may just stick a mechanical pump on the motor and draw through the pump. (I saw at least one instance on the internet where a guy said he’d done this with success.)
One of my concerns is the fuel pump power, I plan to use the in tank lift pump and I’m only guessing here but I fear that the pump maybe run off the TBI harness. My thoughts are I’ll either give it power (safely of course) or I may just stick a mechanical pump on the motor and draw through the pump. (I saw at least one instance on the internet where a guy said he’d done this with success.)
As you guessed the tbi harness is pretty much standalone, there are a couple of wires for power and that is it.
You can use these wires to power the ignition.
I know at least one is hot all the time and one is key on
I have done this to 2 trucks before, one was an '87 one ton that no one seemed to be able to fix, so we made it get back to work by pulling the TBI. The 2nd was my '90 when I pulled it to install the Proflo4.
The fuel pump wiring is easy to separate from the main TBI harness. And if I remember correctly, the ECM fuse that is hot all the time, provides power for the fuel pump. I didn't check to see if it powered anything else.
I used a fuel filter with a return port on the '87, just before the carb. This truck kept the oil pressure switch in the wiring for the pumps.
Using the factory wire for the coil power works fine.
All of the gauge wiring is separate.
A carb and HEI doesn't require much wiring, an electric choke only adds that one wire, so I would look at the overall wire harness to find out how much work it would be to repair what stays vs the hours to remove it all and install a new harness.
The fuel pump wiring is easy to separate from the main TBI harness. And if I remember correctly, the ECM fuse that is hot all the time, provides power for the fuel pump. I didn't check to see if it powered anything else.
I used a fuel filter with a return port on the '87, just before the carb. This truck kept the oil pressure switch in the wiring for the pumps.
Using the factory wire for the coil power works fine.
All of the gauge wiring is separate.
A carb and HEI doesn't require much wiring, an electric choke only adds that one wire, so I would look at the overall wire harness to find out how much work it would be to repair what stays vs the hours to remove it all and install a new harness.
Working on mine I found that the light blue wire coming off the transmission torque converter lockup runs to the ECM at C7 labeled ‘high gear input’. My question is what is the ECM doing with it and what should I do with it? The other wires coming off the trans have their own plug that plugs up near the stock ECM location under the dash which I’m believing would be the brake switch and the like.
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