1964 wire length

[Don B.]

I have a 1964 coupe with stock gauges. The engine, however, has been changed and many electrically based modifications installed. So, I'm building my own engne wiring harness to address these mods and eliminate un-needed wires. However, someone in the past, before I bought the car, also modified the engine wiring harness when a/c was added.

What I need is the stock length of the 10 gauge wire that runs from the starter solenoid BAT terminal to the +12v bus on the horn relay. This is the wire across which the ammeter (actually a millivoltmeter) reads voltage to determine amount and direction of current flow... ie, how many amperes and whether the battery is being charged or discharged.

Can anyone tell me the stock length of this wire??

TNX, Don

[Richard M.]

Re: 1964 wire length

Don, the red wire from the big lug at the bottom to the forked terminal at top of pic? This one's apx 81". That sound right? It's buried so I'm assuming it's the long length of the harness. This one is no AC.
Rich

[Verle R.]

Re: 1964 wire length

Don,

Since you are redoing the wiring, and someone added A/C, maybe you should consider increasing the size of the charge wire one size; just for more capacity/safety.

Verle

[Don B.]

Re: 1964 wire length

GM Rich - Thanks for the picture and input. Yes, the 10 gauge red wire shown is the one. It runs from the starter solenoid Battery terminal across the car to the horn relay +12v bus. The length of this red wire and its size are important since it is also the external current shunt for the ammeter. You'll notice that a smaller gauge black wire is crimped into the same lug as the red wire on the starter solenoid end and there is a similar black/white wire sharing the lug at the other end of the red wire, the horn relay end. These two smaller gauge wires run directly to the ammeter and allow the ammeter to samply the small voltage drop across the red wire. The voltage drop is indicative of the amount of current and its direction flowing in the red wire. The length and size of the red wire must be fixed in order to be in calibration with the ammeter face.

Since my car had been modified years ago by someone, I can't count on the length of the red wire to be as GM intended, which is why I ask.

On a side note: It's very important that the red wire never opens up (becomes disconnected) leaving just the ammeter wires still in place. All the current demanded by whatever is 'on' in the car will try to flow through the ammeter which won't do and may even damage the meter. So, the condition of those two crimped terminals at either end of the red wire are vital to the health of the ammeter.

If you can measure the red wire length and pass the result on to me, it would be appreciated. The only thing I am unsure about is the possibility of a fuseable link associated with this 10 gauge red wire. All the power for everything in the car except the starter flows through the red wire (I think) and it is unfused as far as I can tell.

TNX, Don

[Don B.]

Re: 1964 wire length

Hi Verle -

Was there a size difference between car with and without a/c?? I've assumed the red wire is the same in both cases. The length and gauge of the red wire is very important in order to keep with the ammeter calibration. However, the gauge could be changed once the length and gauge of the original red wire are known. The original wire resistance could be calculated from these two parameters and, once the resistance is known, any gauge increase could be handled by shortening the wire. The idea is to keep the resistance constant since that is what causes the voltage drop measured by the ammeter.

The best replacement for this arrangement would be to buy or construct a shunt built for this purpose that is short in length itself. Then a much larger gauge wire of nealy any length could be used.

TNX, Don

[Verle R.]

Re: 1964 wire length

Don,

I don't know for sure, but suspect, the red wire is the same size for A/C or not in the original wiring harness. That is a good question that maybe someone else can answer.

The reason I suggested a larger charging wire is, when people add A/C to a car they often add other devices that increase load on the electrical system which leads to an alternator that produces higher amperage than stock. This higher load can cause trouble.

If this is not your case you will probably be safe with the 10 gauge wire.

The larger wire will produce less voltage drop so the gauge will show "other than normal" charge or discharge. If you want to increase the voltage drop you would actually have to increase the length of the red wire.

The proper correction for this is to change the gauge circuit, (change the resistance), to normalize the reading for the size/length of the red wire.

Verle

[Don B.]

Re: 1964 wire length

Yes, you're right Verle - the larger gauge wire would have to be longer to keep the resistance the same. I'm a little out of it today fighting a cold off and didn't get any sleep last night.

The interesting thing about having people of unknown backgrounds work on a car is that changes are made without consideration for the original specs. My '64 was originally not an a/c car so the alternator was on the passenger's side. In adding the aftermarket a/c, the alternator was moved to the driver's sice of the engine. The original harness was retained and modified with wire splices as needed. So, some of the wiring is much longer than it needs to be - namely, the alternator (single wire style) output wire and I think there are others like it. I have yet to completely unwrap the old harness to see what else is lurking there. The car also had a MSD capacitive discharge ignition and distributor. In addition, I've added a radiator fan (with aluminum radiator), an electric water pump and an electric fuel pump. Power for these items will not come through the 10 gauge red wire, but through separate fused circuits that cnnnect to the battery at the starter solenoid.

thanks for your input.
Don

[Verle R.]

Re: 1964 wire length

AH HAH!!! More devices, more power!

Don,

I have added some of the same things to my car. I added a separate small fuse block fed by a separate feed wire and use solenoids to control the compressor, fans, etc. Just trying to keep the big loads off the main wiring harness.

Verle

[Don B.]

Re: 1964 wire length

Yep, that's what I intend to do as well. You bet... more power! R-R-R!!
Don

[Wayne M.]

'63-65 A/C harness 2987814; 10 gauge is 117_1/4"

A/C harness is longer than base (P&A Group 2.525 and Gr 9.276). Regular harness is as Rich has shown. His should have a 12 gauge wire from starter BAT terminal to horn relay 12V+ bus. Air cars have a 10 gauge wire here, as you've noted. In pic, you can see the starter wires and BAT 12V connection on the right; in the middle of the picture are the two brass spaded and shrink wrapped connections to the horn relay. The 10 GA wire is the biggest red on the left of the non-soldered spade.

This length is as I measured, from center of attaching bolts/screws. Can take other measurements for you off this example, if needed.

The picture is of a repro air harness that I've had for over 15 years, initially to replace the one in my '65 C60, until I found out by comparison that my car's original harness was more intact than I thought -- so it remains.

But, IMHO you're putting too much importance on the length (& resistance) of that big red wire. Otherwise, air cars would have to have a differently calibrated ammeter, which is not the case. I'm no electrical engineer (too bad Jack H. is on holiday) but I believe the shunt is INTERNAL to the dash instrument, so that relative residual resistances in attaching wiring (if of sufficient capacity) does not affect the reading.

[William C.]

Re: 1964 wire length

Per the wiring print, wire size is 12 ga, length is 33 inches.

[Don B.]

Re: '63-65 A/C harness 2987814; 10 gauge is 117_1/

Thanks for your input, Wayne. Yes, the large red wire pictured is the one in question. What was your measured length??

I believe your statement about the internal shunt within the ammeter is correct. However, the internal shunt is about 1.4 Ohms according to a measurement I made. The large red wire carries a lot more current than that flowing through the gauge since the wire resistance is at least 100 times less than 1.4 Ohms. (I've assumed that the red wire is at least 1 meter long.) From what I find, 10 gauge, stranded copper is about 3.34milliohms / meter and 12 gauge is about 5.32 milliohms / meter. Since there's a linear relationship between resistance and voltage drop for a fixed current, I would think there would be a big difference in ammeter reading between using 10 AWG and 12 AWG wires and I'm wondering how GM compensated for this. As you point out however, it may be somewhat moot in that automotive ammeters are not particularly accurate and are generally used to show whether the battery is being charged or discharged. Cost reduction is the name of the game.

In my '56 C1, the shunt is totally internal to the ammeter as it was for most cars way back then. My guess is that as cars became more complex with additional electrical loads (such as a/c), GM considered it easier to route heavy gauge wires external to the ammeter and measure voltage drop across a known length of wire.

TNX, Don

[Don B.]

Re: 1964 wire length

Thanks, Bill. That's the info for which I've been looking. Now I can proceed to design my harness.

Wayne tells me that there's a gauge size difference between cars with a/c (10 gauge) and not (12 gauge). Do you have the same info for an a/c car??

Don

[William C.]

Re: 1964 wire length

I don't have access to my AIM for '64 right now, if you can look at the C-60 section and give me a part number I will check and see if I have the info. Unfortunately my collection is not 100% complete. I do know that when the engine wiring was consolidated into one harness in 1966, and '67 the alternator feed was upped to 10 gauge, and I have a print for the '65 MY with the A/C wiring layout that uses 12 GA wire to the Alt, so I would assume the same would be true of '63-64. Length on that one from the alt stud to the horn relay is 33.6 inches.

[Don B.]

Re: 1964 wire length

According to my AIM C60 E2.00, the engine harness PN is 2987814, Harness Asm - Eng wiring.
tnx, Don