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Old 03-13-2013, 09:55 AM   #1
NordicSaab
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Default Ballast Resistor getting very hot with key in ignition

Hey RL,

I just pull my engine harness on a 1981 Euro (CIS) 5 speed for some repair work. Did what I needed to and now whenever I turn the key to the On (Not the start) position my ballast resistors get very hot and within a minute or so will start smoking.

I have been doing much research, but cant seem to figure out where the resistors pull power from (seems to be the chassis side of the harness, which I didn't touch) . Any of my electrical gurus have a guess?
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Old 03-13-2013, 09:58 AM   #2
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Forgot to mention. This issue does not occur when the key is out of the car.
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Old 03-13-2013, 10:12 AM   #3
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I'm no guru but check the resistance in the coil and for any abrasions in the wiring to the coil.

The resistors are powered whenever the car is ON. The power is supplied by the wire between the resistors when cranking. Your problem is a short on the "out" side of the resistors.

Find a wiring diagram. Like maybe here: http://www.2010.cannell.co.uk/manual...s_porsche.html
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Old 03-13-2013, 11:49 AM   #4
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did you wash the engine compartment?
if so it could be as simple as the cleaners and dirt from the cleaning operation burning off of the resistors ,
when they are on / key is on, they will get hot.

did you possibly swap the coil wires around?
are any of the wires to the coils pinched
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Old 03-13-2013, 12:43 PM   #5
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Quote:
Originally Posted by Mrmerlin View Post
did you wash the engine compartment?
if so it could be as simple as the cleaners and dirt from the cleaning operation burning off of the resistors ,
when they are on / key is on, they will get hot.

did you possibly swap the coil wires around?
are any of the wires to the coils pinched
I did wash the engine bay including that area, but this is definitely a short somewhere. not only do the resistors get hot, but the wire leading to them does as well.

Is there a switch or device that limits the amperage these resistors receive? I will test Voltage and resistance when I get home tonight
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Old 03-13-2013, 01:27 PM   #6
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did you connect the starter wires correctly?
early cars have 3 connection points instead of the later 2 connection points
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Old 03-13-2013, 02:00 PM   #7
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Quote:
Originally Posted by Mrmerlin View Post
did you connect the starter wires correctly?
early cars have 3 connection points instead of the later 2 connection points

This is one of my top concerns. I thought I put them correctly, but I could be wrong.

Could someone explain to me what the 2 secondary posts on the starter do?

If I did switch the two wires could it potentially cause this symptom?
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Old 03-13-2013, 02:27 PM   #8
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need a wire diagram to assist here
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Old 03-13-2013, 07:58 PM   #9
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Need a wire diagram but, to contribute, newer cars don't have a resistor terminal on the starter because it's not technically points/distributor ignition, not in the traditional sense. It's there so that the starter draws the most power until the motor is started and the key is in run position not start position. So that the starter gets as much power as possible.
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Old 03-13-2013, 08:07 PM   #10
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open the 14 pin connector see if the wires may be shorted together
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Old 03-13-2013, 08:22 PM   #11
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Actually, with the key on, there is current flowing through the ballast resistors to the ignition coil.

The resistors do get very hot, in normal operation.
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Old 03-14-2013, 10:24 AM   #12
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Quote:
Originally Posted by NordicSaab View Post
Hey RL,

I just pull my engine harness on a 1981 Euro (CIS) 5 speed for some repair work. Did what I needed to and now whenever I turn the key to the On (Not the start) position my ballast resistors get very hot and within a minute or so will start smoking.
I cannot offer an explanation but the same happened to me with my '79 about 8 years ago. While troubleshooting some starter/solenoid problems, I was measuring voltages in that area and had the ignition key in ON position. I don't remember how many minutes I had the switch in the ON position but when I got out from underneath the car, I saw smoke coming out from under the hood. I immediately shut the ignition off and opened the hood. It was very clear what created the smoke. I remember actually touching the resistor and almost burnt my finger. Allowed it to cool off, then tried to start the car. It started fine without any indication of a problem. I repeated this test several times over the next day or two thinking that it might eventually fail but no such luck. 7-8 years later, the same resistor is still in place and working, though I bought a back-up, which is in the car at all times.
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Old 03-14-2013, 02:59 PM   #13
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Quote:
Originally Posted by 928nut View Post
I cannot offer an explanation but the same happened to me with my '79 about 8 years ago. While troubleshooting some starter/solenoid problems, I was measuring voltages in that area and had the ignition key in ON position. I don't remember how many minutes I had the switch in the ON position but when I got out from underneath the car, I saw smoke coming out from under the hood. I immediately shut the ignition off and opened the hood. It was very clear what created the smoke. I remember actually touching the resistor and almost burnt my finger. Allowed it to cool off, then tried to start the car. It started fine without any indication of a problem. I repeated this test several times over the next day or two thinking that it might eventually fail but no such luck. 7-8 years later, the same resistor is still in place and working, though I bought a back-up, which is in the car at all times.
And if you went out and touched it today...the same burn would occur.

A ballast resistor reduces the"incoming voltage" to a lower voltage, by turning that current into heat. If you clean and get oil onto the resistor or the white heat sink material, it will smoke.

All normal.
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Old 03-14-2013, 06:17 PM   #14
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Originally Posted by GregBBRD View Post
And if you went out and touched it today...the same burn would occur.

A ballast resistor reduces the"incoming voltage" to a lower voltage, by turning that current into heat. If you clean and get oil onto the resistor or the white heat sink material, it will smoke.

All normal.
Greg, that is comforting to read but there was nothing comforting about the smoke that was coming out. I know they run hot but this didn't seem normal. I could be wrong, it had been 7-8 years since this happened to me, but I don't recall having sprayed anything onto the resistors. What was on them was there before and they didn't smoke during regular use before or since. Almost seems as if there was more heat generated with the ignition ON - engine OFF than when the engine is running. However, I am reluctant to test this theory because I may not be lucky 2nd time. I'll just avoid leaving the ignition key in the ON position any longer than absolutely necessary.
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Old 03-14-2013, 06:36 PM   #15
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Quote:
Originally Posted by 928nut View Post
Greg, that is comforting to read but there was nothing comforting about the smoke that was coming out. I know they run hot but this didn't seem normal. I could be wrong, it had been 7-8 years since this happened to me, but I don't recall having sprayed anything onto the resistors. What was on them was there before and they didn't smoke during regular use before or since. Almost seems as if there was more heat generated with the ignition ON - engine OFF than when the engine is running. However, I am reluctant to test this theory because I may not be lucky 2nd time. I'll just avoid leaving the ignition key in the ON position any longer than absolutely necessary.
There's air blowing on the resistors, when the car is moving. They will get hotter when sitting still.

Go stick your finger on them after 30 minutes of running.....same burn.
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A mechanic who used to work for me would say: "A parts supplier or a person working on a car needs to be 5% smarter than what he is working on, to be successful."

We would laugh until it hurt and then fix whatever was sitting in front of us that someone had completely screwed up.

The longer I spend reading and seeing what people build and do to their 928s, the less I laugh these days.
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