Topic: yet another wiring question on my 78 T/A

[Rick Fox]

Hi folks,

I have another wiring question in reference to my 78 T/A 400.  I understand the pink wire coming from the firewall is supposed to power the coil.  (I’m guessing the wire is a #12.)  There is also a smaller brown wire that runs with it in the harness that has a factory female end.  I understand this is supposed to be the tach wire.  My question is: there is another #12 brown wire with these two.  Does that go to the starter?  (There is no purple wire coming from the firewall.)  Also, there is a red wire apprx. #12 that runs from the passenger side of the firewall with the A/C wires.  Does this wire go directly to the alternator? 

Here’s the deal, I hooked the red battery wire to the starter and ran the smaller lead wire attached to it directly to the alternator.  I then ran the red wire from the A/C loom to the alternator.  I then hooked the larger brown wire to the switch side of the starter.  When I turn the ignition there is no power to the pink wire that's supposed to power the coil, however I have a faint (barely lights up the tester) signal from my tester throughout the entire fuse panel below the steering column.  I’m at a total loss.  (I never claimed to know much about wiring anyhow)  I’ve looked at several wiring diagrams and cannot make heads or tails out of my problem.  I did get the motor fired up using a temporary lead wire from the battery to the coil.  I could really use the help folks.  This car has so much potential, but I’m about to pull my hair out right now.  Please give it some thought and get back with me.

Thank you all in advance for your time.

[gilbertsta]

pictures get best responce...

[Rick Fox]

I'll get some photos uploaded tomorrow.

[eroc022]

yeah that will help, so far you have listed everything ok, the only brown wires under the hood, are tach, and an alt wire, but it should be in a plug with a red wire... its the common lead on the alt...... then there is a tan wire for the brake switch on the proportioning valve, and either a tan/brown/green wire that goes to pulse wipers.... all have plugs on the end and only go to one spot....

[Rick Fox]

Eroc,

The majority of the wires still had the correct ends on them.  I found the green wire went to the heat censor and the blue wire went to the oil sending unit and so on.  As far as the alternator there are three wires ran together, two of which are made into a factory plug.  The other had an eyelet on the end and was in the same harness.  I’m assuming that it’s correct for me to run a wire direct from the battery to the alternator?  Really the two #12 wires (pink and brown) are the hold-up.  I noticed the large brown (not the tach) came out of the plug in the firewall where most diagrams indicate a purple would be.  This was my reasoning for running it to the switch side of the starter.  The smaller brown wire (tach) came out of the firewall slightly above the large plug (the one with a bolt in the center) in the firewall.  It was in a smaller harness along with the cruise control wire and windshield wiper motor wires. 

Is it possible that lack of a chassis or engine ground could be the problem?  I’m assuming this would account for the faint light from my tester when checking the fuse panel.  I also noticed when I would check the fuse panel I would get a “clicking” sound from somewhere on the steering column every time I made contact with a fuse…….  Let me know what you think……………………… 

[eroc022]

Ill have to look at my diagrams... Ill have a definate answer for you after a few hours.... I am about to hit the sack... you have described everything really well, and seems like you know where alot of it goes... but like I said, that wire is throwing me off, a picture of it... and what kind of connector/terminal is on the end should help too....

[Rick Fox]

No connector on the end of either wire.  I’ll get a few pics posted on here.  Thanks for all of your help thus far.  It’s very much appreciated.

[Rick Fox]

this is the red wire coming out of the firewall with the A/C harness

[Rick Fox]

This is the the pink wire (doesn't look pink in the photo) I've been rambling about. 

[Rick Fox]

Hopefully these pics will make it easier.  I need to get power to the pink wire so it will be hot when the key is on.

[eroc022]

[eroc022]

now from what I understand, the wires coming out of a grommet above the fuse block is your options....cruise control, tach, and pulse wipers.... should also be a vacuum line for your cruise.

and now from what I am thinking back to your original question,  if you have everything hooked up like the diagram I posted, and all your grounds are in place, which should have one at the back of the passenger side head to the firewall, (there are more but this is an easily serviceable location) you should have a good ground for your chassis, if all is good there you can move to the underside of the dash electrical....

on a sidenote, I hope you have your alternator hooked up as that is one of the main power blocks on these cars...

if you still need help breaking down connections and wires post it up and I will help ya...

[brian c]

I think Evan's got you headed on the right path.

If you still don't have power to the starter once you get your grounds connected I would suggest the following:

Check the connection & functionality of your neutral safety switch. It's up on the column and is tied into your transmission shifter. If the linkage between your tranny is missing OR misaligned, you will not start your car in a stock setup. It can be jumpered for testing, just make sure your car will not take off on you when you do this as it will start in gear!

Only other thing I can offer up is that I do have a 10G wire running from the + battery post of the battery to the alternator. That gives me full power to the car. I should add a fuse to it at some point to prevent a fire under hood, I've just been lazy.

[Rick Fox]

Thank you for the diagram!  After comparing it to the plug in the firewall on my car I’m wondering if it’s possible I have the wrong plug?  I noticed my wires are in different places than what your diagram indicates is correct.  I’ll post a picture momentarily.  With the way I had everything hooked up my fuse panel was always hot.  Also, I’m back to blabbing about having no purple wire and also no power to the pink wire.  Would having the wrong motor harness explain why I’m having so many issues?

[Rick Fox]

this is what was on the car when i got it.