New member with a question

[Paul83]

My name is Paul and am from the Houston area. I have recently aquired an 83 GMC shortbed with a 305. Not sure if it is a 700r4 or not, but it is an automatic overdrive tranny. I also got an 85 chevy cab that had a 3 speed auto in it. The the 3 speed had a 2 wire plug for back up lights. This is going on the 83. The 83 trans had a 4 prong 3 wire connector that plugged in to it. Will the overdrive trans work without the wires being hooked up? I hope the only problem is I won't have reverse lights. I will post pics of the truck sometime tomorrow. Thank you for any answers.

[cmyc5575]

Originally Posted by Paul83

My name is Paul and am from the Houston area. I have recently aquired an 83 GMC shortbed with a 305. Not sure if it is a 700r4 or not, but it is an automatic overdrive tranny. I also got an 85 chevy cab that had a 3 speed auto in it. The the 3 speed had a 2 wire plug for back up lights. This is going on the 83. The 83 trans had a 4 prong 3 wire connector that plugged in to it. Will the overdrive trans work without the wires being hooked up? I hope the only problem is I won't have reverse lights. I will post pics of the truck sometime tomorrow. Thank you for any answers.

Welcome to the forum!!! Idk much about the wiring on the trans, but someone here should know. Always be prepared with pics.

[andrewmp6]

I think it should be fine but wait for someone else to ok it before driving it like that.

[D13]

Sort of.
The back up lights are on the column not in the trans. So you shouldn't have that issue no matter what.
The only overdrive auto originally available in this timeframe is a 700R4, unless someone has swapped in a 2004r (unlikely but possible). If you do a search you can find out how to identify th trans' by the shape of their drain pans. It will shift gears without the connector plugged in. What you lose is the lock up converter which is significant (about 10% fuel economy), and it generates a lot more heat. Short drive, being easy on it, OK. Push it hard or tow and it will cook.
The 3 speed plug is different internal wiring. I'm guessing it's a 350C (again search and look at the pans). The wiring is different between the two.

[TexasJeff]

Hey Paul welcome the the forum, from a fellow Houston area member, I am from the Tomball area.

I would have to agree with D13 on his advice

[Your41Plague12]

If it's an 85 with a 3-speed auto, it's a TH400 from what I understand. I thought they quit using the TH350 around 1981ish. Someone please correct me if I'm wrong, I would like to know.

[Paul83]

Ok. So I have got some more information. There was one wire to the fuse box, the other 2 wires hooked up to the brake light switch. Down the line 2 other plugs were picked up in the harness 1 looked like it went to the a/c I think. I am going to delete those 2 plugs and hook one back to the fuse box and install the brake switch from the donor truck and hook it up the way it was in the original truck. I will let you know when I get time what happens.

[piecesparts]

You stated that it had overdrive. That would eliminate the thought of a 350C tranny. THe 350C is a lock up converter modified 350 3 speed tranny, where the 700 and 200 R4 trannys had the lock up and the OD on the shifter. My 84 GMC and my son's 86 Silverado both came with the 350C trannys and have long since been removed from them. We no both run a modified 700 R4 tranny in our trucks, but the lockup feature and the lock up converters have been removed. I do beleive that you could get a little better economy with the lockup, but when we changed trannys, this is what we went with at the time.

I agree the backup light switches are inside the cab, and the plugs on the side of the trannys are for the lockup features, which are usually triggered from a vacuum switch on the top of the engine.