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Old 09-08-2014, 06:33 PM   #1
rdgt67
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70 gmc back up lights

I have a manual column shift and I found the backup switch on the trans. There is only one wire going to it. It is cut iff so no idea where it went. Research doesn't clearly show the wiring. The replacement switch shows 2 post. Any comments??
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Old 09-08-2014, 07:53 PM   #2
geezer#99
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Re: 70 gmc back up lights

The wire to the tranny is part of the tcv system. Transmission controlled vacuum switch. The wire clips to that post on the tranny which is the ground for the switch which should be up on the intake or on the firewall. It's function is to provide vacuum to the vac pot on the dizzy when you get into high gear.
Your backup switch is on the steering column down close to the firewall on top of the column.
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Old 09-08-2014, 07:56 PM   #3
rdgt67
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Re: 70 gmc back up lights

I dont have any of that stuff. I have a 250 cid and the vac for the dizzy comes of the carb.
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Old 09-08-2014, 08:09 PM   #4
geezer#99
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Re: 70 gmc back up lights

You very well might but know you know what it's for.
Did you find the back up switch?
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Old 09-08-2014, 08:12 PM   #5
rdgt67
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Re: 70 gmc back up lights

Have to go look. Haven't done that yet but I will. I want to them operational. Its a 3 sp manual. Will they make a difference?
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Old 09-08-2014, 08:22 PM   #6
geezer#99
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Re: 70 gmc back up lights

The tcv won't change anything for you.
Back up lights tell grandma in her prius you're backing up. Handy if you need to fight a ticket.
Take a pic of your motor and firewall. Tcv might still be there or not.
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Old 09-08-2014, 10:40 PM   #7
rdgt67
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Re: 70 gmc back up lights

Geezer, My hat is off to you. I learned something. The tcv is long gone and the b/u switch is where you said. Not going to try and resurrect the tcv system. Thanks for the info!!
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Old 09-09-2014, 07:09 PM   #8
kitsbeach
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Re: 70 gmc back up lights

Quote:
Originally Posted by rdgt67 View Post
Geezer, My hat is off to you. I learned something. The tcv is long gone and the b/u switch is where you said. Not going to try and resurrect the tcv system. Thanks for the info!!
Can you post a picture of the back-up switch.?

I found the wires for mine but it still not obvious how it hooks up as nothing seems to move when I shift into reverse so I don't understand what would activate the switch.
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Old 09-09-2014, 07:19 PM   #9
rdgt67
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Re: 70 gmc back up lights

Took my switch out and it appears that part of the rank is broken off. Does anyone gave a picture of a good one and where x6an I buy one. My searches havent turned up anything.
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Old 09-09-2014, 11:02 PM   #10
rdgt67
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Re: 70 gmc back up lights

That's not it. It mounts on top of tge steering column at the base near the firewall. Found some good pictures by doing a search. The LMC site sells them but its not a good picture. Wanted to be sure mine is broken.
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Old 09-10-2014, 01:07 AM   #11
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Re: 70 gmc back up lights

is this it.?

And do you know how it mounts or is it obvious.?
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