Demond's Muscle Car

Thanks every one for all of your help in the past. I'm working on a 1967 Cutlass Supreme Holiday Coup. But these are many of our cars.

I need to replace the 10 ohm resistor wire that runs from the Engine & Dash Connector to the ACC Terminal on the Ignition Starter Switch. I have read everything from just using 16ga copper strand wire to soldering a 10 ohm resistor on 18ga wire. Me thinks that GM in their infinite wisdom use the resistor wire for a reason. Me no want fire under the dash.

My question is two fold, Sir, might you know of a source for the resistor wire?? Or what would the wattage rating be for the 10 ohm resistor??

The equation I'm using is E= I x R where E is volts; I is amperes; R is ohms. Knowing that 12V is from the system and I'm looking for 10 ohms of resistance I get 1.2 amperes. Then knowing W= E x I where W is watts I get 14.4W. Am I in the ballpark??

m371961

I would use a 14 gauge wire and a ballast resistor from a late 60s Mopar. Why complicate it?

MDchanic

That resistor wire was eliminated in 1968, without any other changes being made, that I know of - I think it's just fine to run a regular copper wire in its place.

Check with Stellar to be sure (and to get an explanation of why they used it in the first place). He's the expert.

- Eric

Demond's Muscle Car

MDchanic,

I shall do that. As I state before in the A/C Heater Control Head post,..."I don't wanna be that guy anymore...". Funny how you claim not to be an expert because you are to me.

M371961
I'm actually talking about the resistor wire that couples thru the Engine & Dash Connector at the firewall ultimately connecting to the voltage regulator #4 terminal. I have installed a 10SI alternator and rewired having used data from this sight.

You guys are the absolute best!!!!!!!

MDchanic

Oh, you put in a 10si internally regulated alternator?

You can definitely replace that resistor wire with plain copper, then.

- Eric

nsnarsk65cutlass

Not sure if i'm reading this correctly.When did they use a resistor wire on he ACC terminal?Isn't that the left rotated position on the IGN switch?Ign run has resistor wire from firewall bulk head to ignition coil right?Ohms law,ohms =volts x amps

stellar

If you are using an indicator light for the 10SI a resistor is not necessary. The light will act as the resistor. If you have no indicator light in the circuit a resistor should be used.

m371961

Sorry, late night quick answer.

MDchanic

So, Stellar, essentially, they used a 10Ω resistance in order to be sure to tickle the alternator when the engine first started, then realized that the current flow through the bulb alone did the job well enough, and saved a few pennies on the length of resistor wire, right?

Interestingly, at a nominal 12V, a 10Ω resistance will pass 1.2A
The specified ALT lamps for 1967 were either the 194 at 270mA or the 158 at 240mA, creating a typical tickler current for that year of 1.44 to 1.47A, while starting in 1968, the specified ALT lamp was the 161, at 190mA, with no separate resistor wire, for a current of only 0.19A, or roughly a tenth of what had been specified the year before (if they had felt they needed more current, they could have used a lamp that drew more, but instead they used a lamp that drew less).

- Eric

oldcutlass

All my schematics just show a brown wire from the regulator to the indicator lamp. No mention of a resistance wire.

MDchanic

From the 1965 and '66 CSMs:



- Eric

oldcutlass

His is a 67... did not look at 65/66.

MDchanic

It's in the '67 book, too, but that one is not scanned as clearly, so it's just a blur - Hey, I've got to work with what's available.

- Eric

oldcutlass

I guess I missed it.

MDchanic

Not hard to do:



- Eric

Octania

South Park - "look MORE closelier"

oh yeah there it is

stellar

Some cars don't have an indicator light, so the resistor is necessary. I am guessing, but since some cars have the lite and resistor my guess is it is a redundant system where if the lite fails the alt will still charge. OR one wire harness works for all. There are multiple regulators and diagrams depending on years and models.

stellar

A 10 ohm 10 watt ceramic resistor works well.

Demond's Muscle Car

Hey guys,

Thanks for all the input. It is my understanding that what Stellar says is correct about the light and the resistor wire being a built in redundancy. Since I'm using a 10SI (might change to a 12SI) I have routed the Brown wire that is in the Engine Compartment to the #1 Terminal on the Alternator. I still would like to have the redundancy. I kinda think that just using a 16ga or 18ga copper stranded wire will work like MDchanic says but I'll go ahead and solder a 10 ohm 10 watt ceramic to a 16ga length of wire. I'm grinning ear to ear...CO is the absolute best!!!!!!!!

Demond's Muscle Car

Man, I need to learn how to post them pics like MDchanic

My 1967 CSM cd version is also blurred but it is visible once you zoom in, some what.




Fig 12-3 Wiring Diagram (34, 36, and 38 Series, V-8)
nsnark65cutlass
You are correct about the ignition position, but we are talking about the charging excite circuit.

stellar

Just a thought here and probably not of much use, but did you ever notice that if you measure resistance of a bulb with a meter out of a circuit and again in a circuit it will change as it gets hotter in use? Also I would not recomend not using a resistor in this line as regulator damage may be a result, so be sure to use some type of resistor.

MDchanic

Stellar, I've got a question. I'm not being argumentative, and you know that I think about these things until they're fully thunk.
Also, I would never object to putting a 10Ω resistor in the exciter wire if one wanted to.

All that being said, If the facts are:

• The 10Ω resistor is specified for all 1965-'67 cars
• The 10Ω resistor is not specified for 1968 and later cars
• There are no other changes in the wiring of the charging system for these years
• The specified light bulbs change from '67 to '68, but the current draw of these bulbs only changes 80mA compared to the 10Ω resistor's passing almost 1.5A
• The Parts Manual shows the same 37, 42, 55, and 60A alternators listed from '65 through '69
• The Parts Manual shows the same regulator listed from '64 through '69 for all cars, except those with RW Defoggers, which have the heavier regulator

then I can only conclude that the 10Ω resistor is unnecessary, so long as you have an ALT warning light wired in.

Since you know a lot more about charging systems and parts than I do, I would like to know if you think I'm missing something here, which I freely admit that I may be.

Thanks,

- Eric

oldcutlass

I think what the resistance wire provides is a redundant excitation for the voltage regulator to still engage the VR in case of a lamp failure. So I would put in a 10w 10ohm resister if I could not find a suitable wire.

stellar

Eric, I think you out thunk me as usual. I'm not a very good thunker. Actually I am a bit on the slow side (seriously). I think as little as possible so I don't use it all up. I'm getting old and don't want to run out too soon.

I think (darn, there goes another one) you have a very good handle on the issue. The resistor is wired parallel with the lite so if one fails the system will still work. It isn't a critical issue as to the resistance as you can tell by the changes. I have even excited a 10SI with a flashlite bulb and 2 D cell batteries. It is possible the changes were made because 1968 was the first year 10SI alts were used. Not many models used them, but it was the introduction year of the 10SI, so maybe the wiring changes were made looking to the future. I agree as long as there is a lite the resistor is not necessary.Attachment 105444

Attachment 105445

Attachment 105446

MDchanic

Ah HA! Now, that makes sense.

Since the 10si didn't use the same exciter circuit, the extra amp or more through the 10Ω resistor wouldn't have been such a good idea, so, because GM tended to avoid making lots of different wiring harnesses (they preferred each option to have its own, for instance, rather than including those wires in the car's main harness), and since the charging system will work without the resistor (so long as the light bulb isn't burned out), they excluded the resistor wire from '68 onward.

Thanks!

- Eric

Demond's Muscle Car

To All,

I missed the excitement, no pun intended, on account of the fact I was burning my fingers soldering in the resistor. Having done some more research, I believe that both of you are correct. Using a un-resistored wire may work for awhile but over time the diode trio of the 10SI and 12SI would eventually burn up. Having a light the will have 500 to 1000 hrs of life should be sufficient to run the circuit. Saving some pennys on the wiring helped GM. I have soldered in a 10W 10 ohm ceramic resistor to the 1-3/4" of resistor wire left on the Engine & Dash Connector to a length of 18ga wire and then soldered that to the spade type connector of the Brown wire that goes in the ACC
Terminal of the Ignition Switch. I read 15 ohm. I think I'm good to go.

Thanks A-Whole-Lotta-Much!!!!

MDchanic

Really? Did the diode boards of every GM car made in '68 and later burn up?



Did you actually solder the resistor to the nichrome resistance wire?
I ask this because nichrome can't be soldered. If you did, then check your joint carefully , as it may be about to slip off.
I'd eliminate that stub of wire and go directly to a connector.

Glad you got it together!

- Eric

Fun71

I don't try to measure resistance of components in an energized circuit. The ohmmeter sources a current in order to determine the resistance, so the additional current flow from an energized circuit will alter the resistance measurement. R=V/I so the additional I from the energized circuit causes an additional voltage drop that corrupts the reading.

Aside from that, as the wire in the lamp heats up, its resistance increases.

MDchanic

Exactly: All incandescent lamps will show essentially Zero resistance when tested with a voltage lower than their rated voltage, because the resistance of most substances, including a light bulb filament, increases with temperature. The incandescent bulb does not reach its operating resistance until it is essentially white-hot, in somewhere between a tenth and a quarter of a second.
The only "normal" way to measure a light bulb's resistance is to measure current and voltage in its circuit and use Ohm's Law.

- Eric

Demond's Muscle Car

MDchanic aka Eric,
You answered your own question as to why 68 and later did not burn up. I do hope your referencing the 10 ohm Resistor Wire.

"...All that being said, If the facts are:

• The 10Ω resistor is specified for all 1965-'67 cars
• The 10Ω resistor is not specified for 1968 and later cars..."

Yes, the 60/40 NiChrome end of the remaining piece soldered to the Resistor

Lead with just minor difficulty as it was soldered in in situ. Conversely the Resistor Lead was difficult to solder to the 18ga, but I made a good joint. Tugged on both ends.

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Demond's Muscle Car

Kenneth,

It would be quite foolish to attempt to, as you say measure resistance in an energized circuit. You would want to measure amps or voltage in an energized circuit.

Eric/ Kenneth,
No where did I mention working on the wiring going to the indicator light. Why would you then assume that I was attempting to take a resistance measurement on an energized circuit. I had just soldered together a Resistor to a length of Wire.

A Digital Multi-meter (Ohmmeter) is needed for testing components: An ohmmeter can be used to directly measure an unknown resistance R.

This is the simplest way to measure resistance. It is important to realize
that an ohmmeter can not be used when the resistance is connected in a circuit and a current is flowing through it!


The above is the "normal" way to measure resistance of the circuit I described in the 21st Century. I should have expressly mentioned that the bulk head connectors were both disconnected and the battery was out of the car. I thought that by saying I was Soldering on the Wiring Harness this would not be necessary to mention.
However, Eric I think I may go ahead and go directly to the connector.

MDchanic

If it worked, it worked, but I've never been able to get solder to really stick to nichrome.

As long as the wires are twisted together well, it shouldn't really matter anyway. I believe that the other reason you don't see nichrome soldered is that it is usually used as a heating element, and thus may get hot enough to melt the solder, which should not be a factor in your case.

- Eric

Demond's Muscle Car

MDchanic aka "The Man" Eric,

Heat is a definite concern! I used he highest temp setting of my Radio Shack Soldering Iron. I used a rosin flux and a solder that is suppose to be used to solder to Stainless Steel. I've had the solder for a long time and don't remember the composition though I believe its lead free.

I have even wrapped the wires surrounding the resistor with Thermal Insulation I used Rubberized Electrical Tape over the Shrink Wrap. Yes sir, I twisted them dar wires together!!

MDchanic

That may well be the trick here, since you can't solder stainless steel either.

If you get a chance, I'd love to know what that solder is called and made of, in case I ever run into some.
Don't waste that stuff - if it worked well for this, it's worth its weight in gold.

- Eric