When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Here is the guidance I used to determine which pigtail to get to plug into my former 12 SI plug when I installed a CS-144. Worked super for me...I don't know what the 15si plug looks like but this may point you in the proper direction?
"If you are unsure which adapter to use, measure the resistance of the exciter line. Disconnect the positive battery cable and the alternator plug. Connect an ohm meter between the #1 terminal on the plug end of the alternator harness and the end of the positive battery cable. Turn the ignition key to the "on" position and read the ohmmeter. If resistance is less than 35 ohms, use adapter #8078. If it’s between 35-350 ohms, use #8077. If it’s more than 350 ohms, you have excessive resistance somewhere in that circuit which needs to be repaired, first."
Originally Posted by slickfx3
i have an idiot light,I don't want to blow the new alternator
can i just get the resistor adapter and call it a day?
Here is the guidance I used to determine which pigtail to get to plug into my former 12 SI plug when I installed a CS-144. Worked super for me...I don't know what the 15si plug looks like but this may point you in the proper direction?
"If you are unsure which adapter to use, measure the resistance of the exciter line. Disconnect the positive battery cable and the alternator plug. Connect an ohm meter between the #1 terminal on the plug end of the alternator harness and the end of the positive battery cable. Turn the ignition key to the "on" position and read the ohmmeter. If resistance is less than 35 ohms, use adapter #8078. If it’s between 35-350 ohms, use #8077. If it’s more than 350 ohms, you have excessive resistance somewhere in that circuit which needs to be repaired, first."
which on is terminal 1?
the alt has been removed and the cs144 ordered, I am not going back
"....
Wiring the CS144 required the addition of a resistor to the alt, if you check around you'll find that the resistance on the lead needs to be somewhere between 35 ohms and 500 ohms (depending on who you believe) and with only a gauge, I needed to add resistance (if the car has a batt. light that should be enough resistance) you can check by disconnecting the positive cable and measuring between the cable and the alt wire to see what the resistance is.
I purchased two different adapters, one from a vette supplier, the other from NAPA, that were supposed to be the correct ones with the resistor, neither were. There was a story floating around that a bunch were mis-boxed but if you get one, open the conduit and see if there is a resistor heat-shrunk on the wire, don't trust the part number on the box
Added a 150ohm 2 watt resistor to the line" ****** This is an updated resistor, see comments below where the original one I used was probably undersized for the application in the long run*****
The rest of the info I have is not relevant to your newer car
HIH
M
"....
Wiring the CS144 required the addition of a resistor to the alt, if you check around you'll find that the resistance on the lead needs to be somewhere between 35 ohms and 500 ohms (depending on who you believe) and with only a gauge, I needed to add resistance (if the car has a batt. light that should be enough resistance) you can check by disconnecting the positive cable and measuring between the cable and the alt wire to see what the resistance is.
I purchased two different adapters, one from a vette supplier, the other from NAPA, that were supposed to be the correct ones with the resistor, neither were. There was a story floating around that a bunch were mis-boxed but if you get one, open the conduit and see if there is a resistor heat-shrunk on the wire, don't trust the part number on the box
Added a 130ohm, 1/2w resistor (that's what I had in the junk drawer) to the line"
The rest of the info I have is not relevant to your newer car
HIH
M
That resistor is a little undersized. It seems to me that at 12 volts it would need to dissipate a bit over 1 watt.
Note that the #1 goes with the smaller lead on the connector. I put them next to each other so you could see the alternator and the connector.
Not sure what your 15si looks like but maybe this will help.
I was told i had a 15si, its only 70 amps ,mine looks the same, i have the alternator off the car, with the key on , i read 15 ohms on the #1 lead, I do have an idiot light though, but it did not light up, maybe cause the alt is off the car?
If so, then I would just go get adapter #8078 since resistance is less than 35 ohms.
Remember that everything would have been disconnected to take the ohmeter reading to begin with.
Originally Posted by slickfx3
I was told i had a 15si, its only 70 amps ,mine looks the same, i have the alternator off the car, with the key on , i read 15 ohms on the #1 lead, I do have an idiot light though, but it did not light up, maybe cause the alt is off the car?
That resistor is a little undersized. It seems to me that at 12 volts it would need to dissipate a bit over 1 watt.
Yeah your probably right. When I did the initial calculations it worked out to about 1.1. People were using 5w resistors and the likes. The painless harness was 2 or 3 watts. I didn't have anything in stock that big so I put the 1/2w one in.
Strange part is it works fine (over a year but certainly not many miles) and doesn't heat to speak of.
Probably should step up to at least a 2w just to be safe
M
There is something not accounted for in that measurement guide that makes your measured number completely wrong because you will still be fine without the resistor adapter.
The bulb resistance will increase when it lights with the key on and the engine not running. A 2 watt bulb has 72 ohms of resistance assuming it is rated 2W at 12V. If the bulb is rated 2W at 14V then the resistance is 98 ohms.
The bub would have to be a 4W @ 12V rated bulb before you need to worry about the resistance being below 35 ohms. Those cluster bulbs are not 4W bulbs. I'm doubting the bulb is even over 2W and is most likely around the 1.5W range.
Mooser - the resistor only sees voltage with the key on and engine not running. So, if you always immediately start the car when you turn the key on then you won't damage that resistor because it can handle a short overload.
Now, it's not an ideal situation because the resistor could blow if you happen to leave the key on for a bit before cranking the engine. It really depends on the quality of resistor. It could take 1W for a few minutes or it could fail within 5-10 seconds. I've tried to burn-out 5W wirewound resistors and one took around 30W for a few minutes without failing. It was glowing red for most of that time too.
Mooser - the resistor only sees voltage with the key on and engine not running. So, if you always immediately start the car when you turn the key on then you won't damage that resistor because it can handle a short overload.
Now, it's not an ideal situation because the resistor could blow if you happen to leave the key on for a bit before cranking the engine. It really depends on the quality of resistor. It could take 1W for a few minutes or it could fail within 5-10 seconds. I've tried to burn-out 5W wirewound resistors and one took around 30W for a few minutes without failing. It was glowing red for most of that time too.
LOL
I'm usually more worried about taking out the points leaving the key on without starting. (lets not go down that road...)
I've got that part of the harness out right now (again) so it's a good a time as any to step up to at least a 2w
M
There is something not accounted for in that measurement guide that makes your measured number completely wrong because you will still be fine without the resistor adapter.
The bulb resistance will increase when it lights with the key on and the engine not running. A 2 watt bulb has 72 ohms of resistance assuming it is rated 2W at 12V. If the bulb is rated 2W at 14V then the resistance is 98 ohms.
The bub would have to be a 4W @ 12V rated bulb before you need to worry about the resistance being below 35 ohms. Those cluster bulbs are not 4W bulbs. I'm doubting the bulb is even over 2W and is most likely around the 1.5W range.
me harbor freight VOM , died, so I think it's bad numbers bc of the meter
me harbor freight VOM , died, so I think it's bad numbers bc of the meter
No, the number you read could have been correct. But, that number is invalid. The bulb resistance is much higher when it is lit making it perfectly safe to use with your new alternator.
Besides, the C3 has a little bulb in series for the light circuit the same as many cars had which came with your new alternator. So, if it works for those cars it will work on your C3.
Yeah your probably right. When I did the initial calculations it worked out to about 1.1. People were using 5w resistors and the likes. The painless harness was 2 or 3 watts. I didn't have anything in stock that big so I put the 1/2w one in.
Strange part is it works fine (over a year but certainly not many miles) and doesn't heat to speak of.
Probably should step up to at least a 2w just to be safe
M
The only time it would have any voltage across the resistor is if the alternator failed or if you left your key in the run position with the engine not running. When the car is running there is no voltage across the resistor and it won't heat up at all, the same is true if the key is in the off position. Nice job on the heat shrink, mine never seems to look that good. Did you use a heat gun?
The only time it would have any voltage across the resistor is if the alternator failed or if you left your key in the run position with the engine not running. When the car is running there is no voltage across the resistor and it won't heat up at all, the same is true if the key is in the off position.
So, don't early C3's run this terminal directly to SWITCHED IGN? That's the way mine is. No resistor or bulb inline. Check your wiring diagram.
I had to add this wire because my alt was not charging.
.... Nice job on the heat shrink, mine never seems to look that good. Did you use a heat gun?
Thanks Jim, I'll take an electrical complement from you anytime.
I try to use a heat-gun unless I absolutely can't. That and I stopped buying the cheap heat-shrink tubing and I'm usually fairly happy with the end results.
11-09-2015, 11:33 AM
resistor adaptor or no resistor from stock 15si alternator to cs144? 1982
So, don't early C3's run this terminal directly to SWITCHED IGN? That's the way mine is. No resistor or bulb inline. Check your wiring diagram.
