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#1 |
Registered User
Join Date: Sep 2003
Location: Mississippi
Posts: 36
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Wiring help on firewall
I've got a '71 Cheyenne, 350 automatic, bought "used" a month ago. After getting the HEI wiring sorted out, and a new wire run from the eng. harn. conn. to the distributor, I thought I'd go poking around to see where "all those other un-plugged wires went. (I downloaded the 67-72 schematics, and 90% of the wires/colors match the original, but it's that last 10% that I'm curious about).
On the driver side firewall, engine side (looking from the front of the truck with hood open, this would be the upper RH side of the firewall, just behind the driver-side hood hinge) there is a "set" of relays mounted to the firewall (with bolts) and a good handfull of (about 6) wires (black, green, light green, blue, brown-white, green-white) coming "from" the relays to a harness that seems to "go no-where". Two of the wires go to what used to be the "backing lamp switch connector" on the old manual tranny, so I've got them figured out (not needed anymore). Two of the other wires (green and green-white) had a "spade connector" simililar to the one on the temp. sensor on the block. Another one "used" to go the an oil sensor gauge on the block, but was disconnected. Not sure what the other wires do, but most thing seem to work okay without any of them. Question: any idea what the "relays on the firwall" were for?? I can't find them on the 67-72 schematic. Any hints/help is appreciated . . . Thanks. Orion 762 |
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#2 |
My other Love
Join Date: Aug 2001
Location: Castlegar B.C. Canada
Posts: 4,085
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those wires are for your TCS (transmssion controlled spark) what they do (or did) is they didnt allow your vacum advance to work unless the transmission was in third gear. The system was also controlled by temperature, hence the thermostat plug. Don't bother get it working again, it is useless and gives you crappy gas milage.
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![]() Castlegar B.C.The great white North (Canada Eh!) Hooter_5@hotmail.com First generation Monte Carlo club pictures of my life |
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#3 |
its all about the +6 inches
Join Date: Jan 2001
Location: Hilliard Ohio
Posts: 2,693
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Hooter, you talking about the relays too..or just the wires.
As far as i know, there are no relays under the hood on these rigs...never seen any on any truck as of yet. (nor in the schematics) |
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#4 |
Registered User
Join Date: Jan 2003
Location: Seattle WA
Posts: 1,466
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Yes I have them on my 71 as well....they don't look like regualr "bosch" type relays....smaller and metal cased....Now I will have to trace the wires down and see as well...
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#5 |
its all about the +6 inches
Join Date: Jan 2001
Location: Hilliard Ohio
Posts: 2,693
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Hmmm, can you get pics? I've never seen this.
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#6 |
Registered User
Join Date: Jan 2003
Location: Seattle WA
Posts: 1,466
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My truck is on vacation right now....so I looked at the pics I already had and you can't see them.....so I will have to wait until she comes back.
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FocuzTech Performance Evergreen Protective Coatings Gatorhyde...the best kept secret in spray in bed lining & protection |
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#7 |
its all about the +6 inches
Join Date: Jan 2001
Location: Hilliard Ohio
Posts: 2,693
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Cool. I'd really like to see this.
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#8 |
Registered User
Join Date: Jan 2003
Location: Seattle WA
Posts: 1,466
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I just removed them about two/three weeks ago and took a wire wheel to the casing to clean em up.....guess they could be fusible links or circuit breakers...
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FocuzTech Performance Evergreen Protective Coatings Gatorhyde...the best kept secret in spray in bed lining & protection |
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#9 |
Registered User
Join Date: Sep 2003
Location: Mississippi
Posts: 36
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Well folks . . . based on Hooters reply, I went ahead and yanked them out with a BFH, then blow-torched the old bolt holes shut so "no one" could ever put them back on again! I trust I was not too hasty? (/sarcasm . . . )
Actually I did a Google search on TCS for these year model chevy's, and many had them installed. The idea was "not to let you have any vacuum advance" until the automatic tx was in 3rd gear. I guess this was early '70's vintage "environmentalism" at it's peak! (Imagine NO vacuum advance until 3rd gear!) When I got this truck, this "stuff" had already been disconnected, but the wiring harness (and odd relays) was still intact on the firewall. Getting those useless wires and stuff out sure made things look a LOT better under there. (Actually I took the wires/relays off very carefully: even noted the "change" in my '71 Chevy Truck Log Book.) BTW - what I "thought" was my "backing lamp switch connector" (unplugged near the tranny down by the header pipes) was apparently the "connector" used by the TCS setup. Earlier threads here had identified this "hanging connector by the tranny" as backup lamp related. With this "new level of confusion" in my mind . . . . okay then, HOW DO you get the backup lights to work?? The "schematic" showed these LG and DG wires going thru the Engine Harness Connector, then on to the fuse box and the "tail and stop lamp harness". On my truck, they went instead to this TCS setup and relays on the firewall. Hmmm . . . Thanks for your help on this . . . Orion 762 |
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