Author Topic: electrical gurus, need your help  (Read 8112 times)

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Offline 78cali

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electrical gurus, need your help
« on: September 03, 2009, 02:16:00 AM »
First of all, hi to Brett.

Okay, here's the deal. I have a 1978 T/A which hasn't seen daylight since 1984. We started the process of reviving her and after 2 years, she's alive!!! The weary 400 was stroked to a 467 and she's just beaming with joy ready to be driven.

Now the problem....we replaced the engine wiring harness with a new one but didn't replace the other half that deals with all the electrical equipment in front. I figured that I didn't have to since when parked many moons ago, the lights, horn, door buzzer, radio, a/c, etc all worked.

Now, I don't have any headlights, no horn, no turn signals, no radio, no blower, no interior lights, no instrumentation panel lights. I mean everything that deals with the front of the car. I however, have power to the rear of the car brake lights, running lights, etc. but nothing in front.

Is there a fuse or something for the front? Maybe a wire that's supposed to be connected to the battery.....please help!!!!
Rene'

Offline 78ta

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Re: electrical gurus, need your help
« Reply #1 on: September 03, 2009, 05:13:59 AM »
What you provided is a good start but with out being there or being able to see pictures we need more details.

You said the brake lights work but do the tail lights work? That may change some of my theory. If the tail lights don't work, you may not be getting 12v from the alternator. Possibly due to a blown fusable link or just a bad alt.

There's a lot here and I've changed several things as I learned more in researching it but I left it all incase something might help. There are a million ways to go about this. Read through it and hopefully something will point you in the right direction.

First thing, check for 12vdc at the two red wires in the bulkhead connector. They are coming from the alternator and I believe they should both have 12v all the time. Now because I suspect a missing ground, first put your negative lead on the neg batt terminal itself and the red lead on the red wire in the bulkhead connector for this check. Then if you do have 12v, move the black meter lead to the sheetmetal on the firewall. If you don't have 12v now, you're missing a ground wire. Probably the large bare braided wire that goes from the block to the firewall.
 
Three of the things you mentioned, headlights, interior lights and horn should all have power all the times so, for those things, you can eliminate the ignition switch or connection to it as a source of the problem. You could have multiple causes but again, it sounds like you have a bad or missing ground in the engine compartment.

The red(pos) battery cable should go over to the alternator. Then another red wire, possibly two,  should come off the alt and go to the bulkhead connector on the firewall. This wire may (probably) has a fusable link in it which could be burnt. The red wire may change color to black or green where the fusable link is. Not because it's burnt, that's just how the schematic is drawn. The schematic is unclear as to whether there is one or two fusable links and red wires going to the bulkhead connector. That easily checked just by looking at your connector. I believe this is the only "main fuse" in the engine compartment. One red wire goes to the corner pin on the bulkhead connector near one of the screws. The other goes one row down and 4 pins away from the first red wire. These appear to be the only red wires in the connector. These are what bring power into the cabin. One of them splits once inside the cabin. One leg goes to the fuse box to the fuse for the tail lights. You said the brake lights work but do the tail lights work? If so, that wire must have power. However, one of the legs that splits from that same wire goes to the horn relay which you said didn't work. This is why I think bad ground up front.  The other red wire goes directly to the head light switch. The head lights ground to the front sheet metal which, if not connected to the negative battery terminal via the engine block to firewall ground wire, won't work.
The blower motor uses a resistor pack to vary the speed of the motor. It is mounted on the a/c box if you have a/c. I suppose it's on the firewall if you don't. Anyway, those resistors can open causing the blower to not work on high speed. It should always be running at low speed when the key is in and on. This is for positive air pressure in the cabin while the engine is running.

If you removed the engine, you may have forgotten to reinstall the braided ground wire the goes from the engine block to the firewall. I believe there is another bare braided ground that goes from the trans to the frame on the pass side. These are very important.

Does the car run? I am wondering if the plugs on the ignition switch attached to the steering column have been plugged in good.

If the car's interior has been taken apart, make sure that you have reconnected the dash/instrument panel ground wire located near the driver side courtesy light bulb. It's just a 12 gauge or so black wire that attaches to the metal dash via a screw into the dash through the eyelet on the wire.  

If none of this helps and you still have the original harness, lay it out and go through it wire by wire and verify what each does and see if there is a wire that is needed but missing from the new harness.
Good luck,
« Last Edit: September 03, 2009, 06:29:08 AM by 78ta »
Randy

Offline 78cali

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Re: electrical gurus, need your help
« Reply #2 on: September 03, 2009, 01:34:18 PM »
Just by reading through your post, I may have the answer right there. To answer your questions first, yes, I do have both brake lights and tail lights. With regards to the car running, yes, it does run. Alternator is brand new and very strong (charged up an almost dead battery in less than 20 minutes of running time).

1. I was just under the car when I came across a wire that you mentioned and it's not connected to anything (similar to a battery cable).
2. I also remember a braided wire by the firewall close to the distributor that's not connected.

I'll tackle these first as these are out in the open and follow your lead with regards to checking fusable links.

WOW, thank you so much!!!!!!! As mentioned, I came across those wires but gave them no concern. I knew they were grounds but thought that it had no bearing to me losing power to the front and inside the car. hehehehe.....you must be laughing and shaking your head. Thanks again and I will update you of my find.
Rene'

Offline turbota400

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Re: electrical gurus, need your help
« Reply #3 on: September 03, 2009, 02:04:20 PM »
Believe it or not, grounds can mean life or death in a car.
Shawn
1972 Chevy C-10
1980 Trans Am Pace Car - 428 ci Poncho in the works
1992 S-10 2WD- Work Bomber/Gas saver
1997 Chevy X-cab 4x4 - Vortec 350

Offline 78cali

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Re: electrical gurus, need your help
« Reply #4 on: September 03, 2009, 03:05:14 PM »
As mentioned, there's a wire similar to a battery cable hanging down and have no idea where it belongs.


The braided wire is bolted onto the firewall, where does the other end bolt on to?


There's also this connector which I have no idea where it should be.


A red wire from that connector leads to nowhere, where should it go?


There are also 2 green wires, one lighter than the other, also from that bunch by the blower
Rene'

Offline brian c

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Re: electrical gurus, need your help
« Reply #5 on: September 03, 2009, 03:37:11 PM »
Pic #2 - loosen an intake bolt, clean the surface, and attach.

Pic #3 - High speed relay for your AC fan.

Pic #4 - red wire should have a white clip on it that plugs into an extension harness. That extension harness connects to your alt.

Pic #5 - those should run into a 2 pin, round connector I believe. Might be square. Either to your AC Line or AC compressor. Would have to do some digging as BOTH are light/dark green. Yes GM fouled up on that one.

1978 Y88, '70 455 HO block bored 0.060, TH350, 3.42:1 gears...Oct '08 Fbodywarehouse Calendar - Woot!
1980 Firebird - no engine/tranny... to be pacecar clone

Offline 78cali

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Re: electrical gurus, need your help
« Reply #6 on: September 03, 2009, 03:52:05 PM »
Thank you!
pic #2 should be easy
pic #3 I don't see any where to plug it in
pic #4 can I just run a wire and connect it to the alt? Since this is connected to pic #3, will this in turn run my blower motor?
pic #5 should be easy as well

THANKS AGAIN!!!
Rene'

Offline 78cali

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Re: electrical gurus, need your help
« Reply #7 on: September 03, 2009, 03:53:11 PM »
What about that battery looking cable wire that's on the passenger side?
Rene'

Offline brian c

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Re: electrical gurus, need your help
« Reply #8 on: September 03, 2009, 03:58:46 PM »
Thank you!
pic #2 should be easy
pic #3 I don't see any where to plug it in
pic #4 can I just run a wire and connect it to the alt? Since this is connected to pic #3, will this in turn run my blower motor?
pic #5 should be easy as well

THANKS AGAIN!!!

In Pic #3 - see the holes on the side of your AC suitcase just behind your hand in the photo? That's where the relay SHOULD be mounted. Looks like its missing. Just need to get one - I think I got mine at NAPA or the like. Pretty cheap to do.

Pic #4 - sure you could. Just use a ring terminal on the end that connects up to the post on the alt so it doesn't slip off. **Yes once you get the relay and the + feed setup your blower motor *should* work - all things being equal.

Your first pic I can't makeout so I'll take a stab in the dark and hope I'm right on one of them...

1. Its a shifter cable that needs to be hooked up to the tranny.
2. Its a speedo cable that needs to be hooked up to the tranny.
3. Its a ground wire that needs to be connected to something - perhaps subframe, tranny or firewall.

Are you sure its a wire???

1978 Y88, '70 455 HO block bored 0.060, TH350, 3.42:1 gears...Oct '08 Fbodywarehouse Calendar - Woot!
1980 Firebird - no engine/tranny... to be pacecar clone

Offline 78cali

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Re: electrical gurus, need your help
« Reply #9 on: September 03, 2009, 04:21:39 PM »
yes, and its thick just like a battery cable it's also bolted on to the subframe
Rene'

Offline 78cali

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Re: electrical gurus, need your help
« Reply #10 on: September 03, 2009, 04:35:08 PM »
This relay that you mentioned, what is it called and NAPA you said carries it? So all I have to do is plug in that black connector to the "relay" and run a live wire to the alt. Am I correct?
Rene'

Offline Rick

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Re: electrical gurus, need your help
« Reply #11 on: September 03, 2009, 04:44:15 PM »
What about that battery looking cable wire that's on the passenger side?

The is called the secondary ground.  One end connects to the subframe, and the other end goes under a bolt on the bellhousing to the block.

Offline 78cali

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Re: electrical gurus, need your help
« Reply #12 on: September 03, 2009, 05:08:46 PM »
Thank you Rick! Is this essential? One end is bolted on but the other end seems to have been cut or the connector is missing and it's so thick that I have no idea what to put there enable to connect it. Besides, it's too short to reach the block.
Rene'

Offline 78cali

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Re: electrical gurus, need your help
« Reply #13 on: September 03, 2009, 05:13:41 PM »
By the way, in relation to my problem, I forgot to mention that the wiper and power windows work and all my gauges. Other than these, no power and no lights.
Rene'

Offline Rick

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Re: electrical gurus, need your help
« Reply #14 on: September 03, 2009, 09:56:24 PM »
Thank you Rick! Is this essential? One end is bolted on but the other end seems to have been cut or the connector is missing and it's so thick that I have no idea what to put there enable to connect it. Besides, it's too short to reach the block.

Well, it's a redundant ground, so it's likely that everything would work OK without it BUT if another ground connection somewhere went funky then you could have all sorts of "ground" problems.  "Ground" problems are kind of like ghosts -- hard to find, hard to pin down, and really sometimes even hard to describe consistently.  If the redundant one on yours has been cut off too short, I'd make up another one.  It connects between the subframe where yours bolts on now and the bolt mounting the transmission to the block.  Most of the time when Billy Bob pulls the engine he just cuts it off and/or forgets to reconnect it because he doesn't understand what it is about.

The grounds on the gen 2 F-body are the weak point in the design.  The only part of the electrical design that's worse than the grounding scheme is the power window wiring design.  That may have well been done by chimpanzees.

Incidentally, the copper braid that bolts to the firewall up in the engine bay is supposed to bolt onto the back of the passenger side head.  You use one of the accessory holes to do that (the heads are symmetrical, so it's the same set of holes used for the power steering pump on the driver's side).