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Old 02-15-2020, 01:32 AM   #1
AASmedic
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Help with underhood harness on a 71 C10

Can anyone tell me what these harnesses and relays go to and what they are used for?? Thanks in advance.
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Old 02-15-2020, 03:18 AM   #2
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Re: Help with underhood harness on a 71 C10

Emissions stuff. Should go down to the transmission
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Old 02-15-2020, 11:40 AM   #3
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Re: Help with underhood harness on a 71 C10

Right- Transmission Controlled Spark. It prevented vacuum advance until the engine was warm enough and the trans was in high gear. It looks like the harness has been chopped off. You can remove it or just ignore it. How is your vacuum advance connected to the vacuum source?
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Old 02-15-2020, 10:40 PM   #4
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Re: Help with underhood harness on a 71 C10

Quote:
Originally Posted by Steeveedee View Post
Right- Transmission Controlled Spark. It prevented vacuum advance until the engine was warm enough and the trans was in high gear. It looks like the harness has been chopped off. You can remove it or just ignore it. How is your vacuum advance connected to the vacuum source?
Makes me wonder if this truck was originally automatic. The connections were just laying behind the engine and not connected to anything. The engine was replaced 20 years ago. Vacuum advance is hooked up to the port on the carb. It has a 4 speed manual transmission. Do I just need to remove this part of the harness?
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Old 02-17-2020, 11:23 PM   #5
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Re: Help with underhood harness on a 71 C10

You can just toss it if you want. The system also worked on manual transmissions, in which case there was a manual switch on the shift linkage (at the transmission) instead of a pressure switch in the valve body of an automatic transmission.
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