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hey elco centro
been a while since i posted. I got my Non-CCC quadrajet and vacuum dist installed on my 1985 305. shes purring like a lion and i love the reman Qjet. Now that Ive deleted the computer i was wondering If anyone whom has spliced in a TCC lock up bypass switch could post up some pics and wiring diagrams of how they did it. I have the THM200c (Metric) trans. I did a basic search but couldnt find any pics and diagrams and im a visual person. you could type up descriptive step by step instructions and I could probably get it but pics are worth a 10000000 words. thanks.
If someone has a link to a thread that covers this feel free to send it
 

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Wow JJ thanks for the quick response. I already have a toggle switch, inline fuse and plenty of wire and connectors. All I need now is the GM pressure switch? My tranny , THM200c METRIC , only has 3 gears I'm assuming it will still work? Also where exactly does the pressure switch screw into in the transmission?
 

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your transmission may already have everything for automatic operation
in it already wired up..
the computer just added just the ground for the solenoid on the lockup,
when it was ready, probly based on VSS/TPS..
.
normally the pressure switch is inside the pan. on the valve body..
I have no idea which port internally, I never had a T200c or 200-4r,
but my 700r4's are supposed to work the same way, mine locks in 3rd and 4th..
the write up by TrannyMike uses a external pressure switch on the
trans pressure test port on the case for a 200-4r,
I'm not sure if T200c is the same ??
a defi-nint answer may be in that thread tho..
.
you can test yours just by hooking up the on/off switch to the TCCground at the computer or case plug..
if the switch is in the trans it should only lockup in 3rd gear,,
and the brake light switch or the 3rd gear switch should un-lock it when
you slow down or brake..
if it don't work right just turn the switch off, till you hit the hiway..
.
for automatic operation
depending on your rear gear ratio, it may want to lockup too early or late
for city driving..
that's when people add a vacuum switch or lockup controller and/or manual switch..
 

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I literally just did this a week ago on my '87 with a 200-4R, using the kit from TCI; I had also changed to a Holley and vacuum advance HEI distributor. Tranny is in the car, so I had her on stands to drop the pan (what a mess; I installed a drain plug while it was out) and worked from below. You have to remove the interior wiring harness and replace with theirs, including the 4th gear pressure switch, exterior wiring plug and the vacuum switch for lockup. It can be wired to a toggle switch also, but I chose vacuum on the carb and it works. TCI has a video on youtube that explained the wiring pretty well also.
 

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looking at the instruction sheet, it would be the B terminal for the ground...
.
as a test
if you disconnect the connector from the trans,
turn on the Ignition switch, and check both wires for 12volts with a volt meter
only 1 should be hot, the other is the ground to the computer..
 

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Discussion Starter #8
• Sorry got home late tonight from my sons practice. I snapped a couple pics just for reference but didn't have time to test the plugs with the test light. I didn't see anything in my Haynes about which pin is ground or anything about the transmission for that matter. But I'll know for sure when I check with the multimeter or test light tomorrow. I automatically assume the green? green/yellow? Green/white? But I don't want to make an ass of myself till I know for sure. Sorry I'll clean everything up tomorrow and post a better pic. It's hard to tell what color the wires are.
• I'm pretty sure the TCC solenoid isn't accessible thru the pan like the 700 and 2004r. I noticed jegs and painless sell aftermarket kits for the 700 and 2004r. If I can make my own harness out of the toggle, fuse, and wire I already have that would be ideal.
• I feel like I found a thread on another forum, maybe gbody or a vette forum, where a guy rigged up a toggle tapping into the ALDL? I'll try to find it again but it kinda makes sense, his description just went over my head.
 

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Ok here are those articles, sorry if this knowledge is common sense to everyone else, I'm just now figuring it out haha


 

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yep, bunches of different ways to do the same thing..
.
here's everything you need to know,
Except what you wanted to know...
Trans TCC.jpeg
I had a answer for you till I saw the "200C NOT USED" on the diagram,,
like the 200c don't have a pressure switch ???
maybe it just uses the VSS 40mph signal to make the ecm happy ??? I don't know..
.
yes
if you ground the F terminal on the ALDL it should lockup the TCC,,
if everything else is working [ power, brake switch, TCC solenoid ]
that is the TCC test terminal.. [ I forget about those ]...

the A terminal in the ALDL is just a ground...
.
and the diagram says its the D terminal on the trans connector
for the ground on the TCC solenoid,, not the B like on the instructions...
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yea that Darbysan guy is purty sharp, he's on here too..
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it is strange that you don't have a Purple wire at the trans,,
so I looked up the V6/200c diagram and the only difference
is the green/white wire is blue...
.
I think I need another nap...
 

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Discussion Starter #11
Wow thanks so much JJ for putting your time into this. Yeah I wonder why it says it's not used on the 200c. I should probably search for the ID number on the trans to verify everything, could've been swapped at some point? It says metric on the pan and the filter and gasket I just replaced fit perfectly. Ordered off rock auto and said it's for 200c
 

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This is what I was going to rig up. This is the toggle switch I have. It has the LED light in the tip. I was thinking of using small blade connectors to go into the ALDL sockets or I could T the wires from behind the test block? I wasn't sure If i would even need the 12v supply to the switch? Do I just need a 2 prong switch? Sorry I'm not the most knowledgeable electrician
 

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the switch should still work with-OUT, the 12v or the light-up feature,
but that's where it gets different..
your using the switch on a ground circuit, after the load..
if its a LED light in the switch, then I don't know ???
LED's don't usually work backwards..
lots of different kinds of switches out there now days..
 

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that specific switch should come with a wiring diagram..
.
most 123 switches have the extra ground for the LED on #1,,
for a positive switched side.. and
the load is on #2 and #3..
.
I think,???, this pic is what you are actually tryin to do, switch the ground..
just leave off the #1 terminal.. switched load on 2 and 3..

elec 3t grnd switch.jpg
.
this is where I found that pic..
the first pic at the web site is more normal,
switching the hot with a ground for the LED..
link to pic
and
heres the search
 

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Discussion Starter #17
Ok I see what your saying. I don't have the package for the switch anymore, so I just went out and tested everything with jumper wire and test lights. I tested pin F with key on engine off and it had power
 

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good test, so the power is going thru the TCC solenoid all the time,
that tells you if there is a pressure switch in the trans its normally closed or broken,,
and if it opens with pressure then the TCC wont work, so probly no pressure switch..
or there is no pressure only in 3rd gear?? I don't know...
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yes F term should be hot, and when you hit the brake it should go out..
that's power from the ignition switch to the gauge fuse and to several other things,
one being the brake switch and TCC solenoid..
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the way they have the switch wired in the pic, F would be on #3 term,
it don't matter if your not worried about the LED, but it might work I don't know..
but the hot side of the switch would be on #3..
and you can see #2 going to the neg-battery post..
 
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