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Old 01-21-2006, 03:42 PM
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electrical problem

I am working on a 1972 Dodge Challenger, originally equipped with a 318, I dropped a re-worked 440 out of a B300 Tradesman, anyway, last week I was doing some dash work and fixing dash lights, cigar lighter, dome light etc. It went well or so I thought! after re-assembling the rally dash, The car would'nt start, I've checked everything I can think of, fuses, distributor, coil, ECU. Symtoms are this, I have no spark from the coil, I only have 5 volts to the pos side of the coil, I believe I should have 12 volts, with the key in the on position, the ballast resistor gets very hot, I replaced most everything in that electrical system under the hood. I'm seeing 12 volts from the starter relay, to the ballast resistor, to the volt meter to the ECU, the only thing I'm not sure of is that I have 12 volts on the right side of the ballast resistor but only 5 volts coming out of the left side which is the side that goes to the pos lead of the coil. Any suggestions?

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Old 01-21-2006, 05:34 PM
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Doc here,

Ok, let's see if I got it...

You have 12 volts constant in "Run" to the ballast from the ignition switch.

You Have 5 volts from the ballast to the coil + side...

You have 12 volts constant to the Ballast while Cranking ("Start" Mode) Correct?

If this is so, 5 volts seems a little low on the coil +, though a ballast, typical is 6 to 9 volts loaded..unless the battery was a little low, or your DVOM was slightly out of calibration..

Pull the cap, rotate the engine until the points are on a low lobe...(closed) Measure the power at the coil + should be 6 to 9 volts , (I think we established that as a parameter) Then , rotate the engine until the points are on a high lobe..(wide open) Measure the coil + again, It should read 12 volts. If not you may have a defective ballast or coil..Or a short between the coil and points.

Quick and dirty test, jumper over the ballast (12 volts to the Coil + side) and try to start it, If it fires and runs, the ballast is headed south..(don't do this too long, It can damage the coil and points) If it won't crank or runs badly check the coil..

To do that, Disconnect the wires from it, you need to set your DVOM for R X 1 on Ohms scale and measure the primary windings...It should read less than an ohm but more than 0.00 If it reads 0.00 replace the coil, the primary is shorted out.

Next measure your secondary , set your DVOM to R X 10K on Ohms scale and measure the secondary, It should read between 10,000 and 11,000 ohms..Much above or below that range, replace the coil. (see Illustration)



If that checks out good, Look at the Dizzy itself, are the points actually opening and closing? Is the gap too wide? shorted wire , RFI Cap or something grounding out the points? Dizzy / Points getting a good ground? (pigtail on the adjuster screw on the points base) Inspect the cap for Carbon sprayed all over the inside of it..

My bet is on the coil primary, or a short going to it.

PS...KEWL username..good 'OL Song, my Ex #3 and I had that as our song..AND it's also good for someone working on electrical problems

Doc
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Last edited by docvette; 01-21-2006 at 05:38 PM. Reason: Cuz I can!
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Old 01-23-2006, 08:34 PM
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1991 pontiac firebird

I really need to know where the sensor is located on the car for the fan to turn on because the engine is too hot to cool the radiator
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Old 01-23-2006, 09:14 PM
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Doc here,

Here is the stock locations for your sensors, NOTE: they may still use a sender in the radiator bottom, so check there too...

ALSO NOTE: the location of the Cooling Relay..Check that also..



Here Is the electrical diagram for the same system..



Note: the Fan Control is PCM supported..not just sender dependant..so the senders could be good and the PCM has a problem.

Check to BE SURE you have a good GROUND at the fan...this will kill it right off..

ALSO NOTE: The fan circuit for B+ to the motor, is supported by a FUSE LINK..check it to be sure it is good..

The relay control logic for the motor relay, (Interface between the PCM and Fan motor) Has a 25 amp fuse on it, Check BOTH of these IF the fan does not run at all.This is the most likely scenario.

Doc
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Last edited by docvette; 01-23-2006 at 09:16 PM. Reason: Cuz I CAN!
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Old 01-24-2006, 05:57 PM
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Low voltage at the ballast resistor and no spark.
These symptoms point to a shorted condenser.
Of course, this has nothing to do with the dash work. Go figure.

vicrod
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Old 01-29-2006, 02:43 PM
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fixed electrical problem

Man, this was a tough one, thanks for the tips, but what I ended up doing was retracing my steps, I was doing dash electrical work when the problem started so I went back and removed the dash gauge cluster and disconnected all the guages except the volt meter....bingo It started right up! I had bought a used Tach on Ebay and installed it, It was bad, I put the old one back in and problem solved! God is good!!
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Old 01-29-2006, 03:12 PM
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Quote:
Originally Posted by SmokeGetsInYourEyes
Man, this was a tough one, thanks for the tips, but what I ended up doing was retracing my steps, I was doing dash electrical work when the problem started so I went back and removed the dash gauge cluster and disconnected all the guages except the volt meter....bingo It started right up! I had bought a used Tach on Ebay and installed it, It was bad, I put the old one back in and problem solved! God is good!!

Doc here,

KEWL! Glad to hear you got it fixed,

Thanks for posting back with the fix,It may help someone else..

That's kinda rare but happens! And the last thing you'd think about...But then again, It's usually the last thing worked on is the culprit!

Doc
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Last edited by docvette; 01-29-2006 at 10:01 PM.
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