[AZ64GP]

Hello,

I'm starting to replace the wiring on my '64 Grand Prix. I bought an aftermarket GM wiring harness (not a OEM-style replacement harness) for muscle cars, and I have a question regarding the ground wiring. The replacement harness I have, which I heard is common for replacement automotive wiring, does not include ground wires for the components. I also have a copy of the '63 Pontiac Body and Chassis manual (with the '64 supplement manual), and there's a lot of good wiring diagrams, troubleshooting, etc., but nothing regarding number or location of grounds for the various parts of the car. At least that I can find.

Have any of you replaced wiring on an old car (if it was a fullsize '64 Pontiac that would be even better), and can tell me where the grounds are or point me in the direction of where I can find a diagram that would show them? Do you know the number of grounds and what is typically grounded? I assume there are one or two main grounds to the frame of the car, and several smaller grounds that are parts of the body wiring harness for the various electrical components. If I even knew what parts are typically grounded in the factory wiring harness (i.e. there's one ground for the taillights and the rear portion of the car, one ground for the front lighting, etc.) My other option is to pick apart the original body harness and trace the ground wires through the harness and see what goes where. I will be replacing the ground wires as I replace the harness, but I want to make sure I'm duplicating the type and number of grounds that the car would have come with from the factory.

I would appreciate any insight you may have on this topic. Thank you in advance for your help!


Chris

[Deadhead]

We will need to know if you have an A/C car or not as those have a few more ground straps. There are some old threads regarding '66 cars and how many ground straps they had originally and their locations. This will be close and get you started as to where to look. The block will have them or the remnants of many of them which will also give you clues.

You are going to be best served by taking your original harness out of the car and comparing it side-by-side with what you have AFTER you label all the functions of the block connectors etc. Pros do this on a plywood sheet so they can secure various parts to keep them straight. Since it is doubtful a generic harness will have some of the specific type connectors used in these cars, I suspect you are going to have to re-use some of them anyway, so this will save you a lot of time. Tape on the device and tape on the wire would be a good way to go. If this is the case, you will need to make or buy a tool to extract the connectors from the plastic blocks by bending their tangs down to release them. Check the bulb sockets carefully to make sure they are the same.

There is not going to be anything easy about doing it with a generic harness, so be prepared to spend some time.

When I did my '63 with an M&H, I was able to chop everything off at the devices and simply match up the new with the old, tossing the cut ends as I went. Took longer to feed the thing from the inside of the car into the engine bay and get the grommet right than to hook up.

Vaya con Dios.

[Stuart]

There's a wiring diagram online at http://www.oldcarmanualproject.com/t...ing/index.html that may be useful - I don't know about the 1964 factory manual but I've found in some cases this set of wiring diagrams can be easier to follow.

In general, you can't have too many ground connections. The front and rear lights are normally grounded right near the lights, either in the trunk or somewhere on the front radiator support. The engine should have three or four ground straps, my '61 has one on each cylinder head at the rear that fasten to the firewall, and one on each cylinder head at the front that fasten to the frame right by the upper A-arms. There should be a couple smaller ground straps between the radiator support and the frame as well, since it's rubber mounted.

[mike nixon]

is this an OE harness or a STREET ROD harness [ IE Ron Francis?}

IMO the ROD harnesses area pain in the ass unless you're building a rod from scratch.

If it's a rod harness the OE diagram will do you very little good.

Mike

[AZ64GP]

Thank you for your replies! I appreciate any information I can get. I think Deadhead has a good idea by laying out the harnesses side by side and comparing them. Thanks to Stuart as well for the wiring diagram link. That's the same or similar to the harness diagram in my Pontiac factory manual, but it helps to have it accessible on the computer too. Mike is right that the OE diagram isn't too much help for the new harness, but it does help me know what wiring goes where and helps understand the various colors of the factory harness wiring. I just wish the OE diagram showed grounds.

The harness I bought is similar to a Painless harness...it's made for GM cars of the 60s and 70s. I considered getting a reproduction from M&H, but I wanted a modern fuse box, and ability to add devices onto the car in the future (i.e. an electric radiator fan, etc.) if I choose. Cost was also a big factor as replacing the harness with a M&H (or similar) would have cost me $2,000 just in harnesses and connectors. I spent 1/10th that for this harness, so even if I spend some money for the reproduction connectors, I'm still way ahead. If I had a rare car or was doing a numbers-matching restoration, then an OEM-like reproduction would have been the way to go. I've already converted it to front disc brakes, replacing the transmission with a later 3 or 4 speed automatic, etc., so complete originality for the whole car isn't as much of a concern.

The harness will definitely take more time as I have reuse or source new connectors, etc., but I'm willing to take as much time as necessary if I can save money and have something closer to what I'll need when the car is complete.

Thanks again for your help!

[64catdroptop]

I suppose I would need to ask: which harness are you replacing? You '64 Prix has an engine harness, a forward light harness, an under dash harness, and a rear light harness. (if you have A/C, you'll also have a harness for that), and also a small harness for your console.

Second, why are you replacing the harness(es)? They are easily restored with some markings (as Deadhead had said), a couple of rolls of good 3M 88 black electrical tape, some small wire ties for markers (where wires split out of harness) and a run through the dishwasher.

Unless your fuse block is so badly damaged that it can't be used, I would recommend reconditioning your original harness. You'd have it done in less than a week just working evenings for a couple of hours.

Nixon's point is well taken - unless you're building a street rod from scratch, the harness you purchased will be a real headache to use.

[Deadhead]

Originally Posted by AZ64GP

I considered getting a reproduction from M&H, but I wanted a modern fuse box, and ability to add devices onto the car in the future (i.e. an electric radiator fan, etc.) if I choose. Cost was also a big factor as replacing the harness with a M&H (or similar) would have cost me $2,000 just in harnesses and connectors.

Thanks again for your help!

Holy Crap! I paid $400 for the complete harness and a headlamp harness from M&H a few years ago.

As Ron says, If you source the spade connectors and some bulk wire, you could easily repair your original depending on the fuse block. Most have extra slots that you could add circuits to. Be cheaper and better to do this even if you have already bought the other one.

[61 389-348]

Originally Posted by Deadhead

Holy Crap! I paid $400 for the complete harness and a headlamp harness from M&H a few years ago.

As Ron says, If you source the spade connectors and some bulk wire, you could easily repair your original depending on the fuse block. Most have extra slots that you could add circuits to. Be cheaper and better to do this even if you have already bought the other one.

I think I paid even less than that for the complete harness from M&H for my 63 GP, although that was 13 years ago. That should be real similar to a 64 GP harness. Install wasn't too bad and took several evenings of a week to complete.

[AZ64GP]

Thank you Deadhead and 64catdroptop for your replies. I did a lot of research into whether I should replace my harness, what route should I go (i.e. generic "street rod" harness or OE replacement harness from a place like M&H), etc. I also spoke to my family mechanic and other friends of mine, who have built or are building hotrods and restored cars, and they all said that I'm better off replacing the wiring harness and should not try to restore it. I didn't want to risk an expensive restoration in the future on 50 year old original wiring, a fuse block that has corrosion, and all in a car that sat outside and hasn't been driven since the early 90s. I have learned too that as wiring ages, the wiring just doesn't carry electrical current as well. For example, I didn't want to put the dashboard back together only to find out that every light in the dashboard is dimmer than they should be because of the old wiring simply not conducting the electricity as well.

To answer 64catdroptop's question, I'm replacing all of the harnesses. I've already purchased the harness for the car, and I'm moving forward, so there's no turning back now with the wiring . I priced the various M&H harnesses (I also got pricing from a company that produces a similar OE replacement harnesses to M&H), and when you add up the dash harness (that alone was $565 last I checked), and all of the various individual harnesses (air conditioning harness, taillight harness, etc.), there was almost $2000 in harnesses when I included any taxes and shipping. The taillight harnesses alone for my '64 were over $350, which is 8' of wire, a connector, and 8 taillight/turn signal/brake light/reverse light sockets. Even with the new harnesses from M&H, I'd be reusing the original fuse block which may or may not be any good as it is corroded. I couldn't justify spending $2,000 in wiring harnesses for a car that will be worth $25,000 when I'm done with it. If this was a numbers-matching restoration of a rare car that would be worth $60,000, then I agree that an OE replacement would be the only way to go. I also realize I will probably have to buy some harnesses from M&H (the console harness comes to mind) and some connectors, but from what I can tell, the generic harness I purchased is pretty complete. Even if I have to buy a small harness or two from M&H and connectors, I'll still be a long way from spending $2,000 for all OE replacement harnesses.

I agree that a replacement harness from M&H would have been easier and faster for me to complete the wiring, but I'm in no hurry. The restoration/restomod of this car is going to be a 5+ year project, and I have help completing it. If it takes me 4 months or longer to wire the car, I'm fine with that.

Chris

[das maler]

Just rewired my 64 safari. I used an american autowire kit. pretty much the same reason, couldn't justify a 2k harness on a 5k car. Took about 20 hrs, 2-4 hrs a night for a week. The key is to have quality crimpers, I bought some pakard, and delphi crimpers used off ebay, having the correct tool for any job makes things easier.

[Willshire]

Back to the original question regarding grounds, if you have your grounds from the block to the chassis and the block to the firewall you should have little problem. I have my ground for my fuel sender still disconnected (replaced floor in trunk) and it still works fine as it is grounding through the gas tank straps. Everything in that car is made of metal and you will notice there are no long grounds for anything. Basically, 6" of wire, ring connector, star washer and sheet metal screw. Done. BTW make sure you buy a $20 kit of assorted star washers and grounding will never be your issue. I agree with putting the harness on a sheet of wood and duplicating it with your univ harness. Old wire only loses its ability to conduct if it is allowed to corrode (turn green). If most of your connectors are in good reusable condition you could cut them off at 6" and solder and heat shrink them to your new hardness thus saving even more.