XJ6 & XJ12 Series I, II & III 1968-1992

Low voltage at coil +; ignition protection?

 
  #1  
Old 09-17-2014, 03:34 PM
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Default Low voltage at coil +; ignition protection?

Hello jaglovers,
about my V12 Daimler double six 1979 series III; D jetronic
I have a low voltage at the coil + VE (3.4 V instead of the workshop ref.value (4-6 V) ( distributor pick-up connector R B Y disconnected)
In order to find the cause, I have followed the white wire at the entry of the ballast resistor and could measure a value of 10V there. After the key contact (white wire at pin 3 inside the car after the key lock) I measure 10.9 (with Key on) (KO: batt=12.7). So I have a (corrosion) resistance in the lock contact which I will try to clean. Anybody has tip on how to proceed?
On the other hand having 10.9 V at the middle entry of the ballast resistors (ign. on), but from there to the coil +Ve I am loosing a lot (10.9 - 3.4= ...) over the resistors, which is a lot. I guess to much. Anybody an idea?
In the workshop manual one mentions an "ignition protection relay"; what are the parameters here? Thanks fr your tips
 
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Old 09-17-2014, 03:48 PM
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Default forgot to mention ball res. values

Originally Posted by patpin View Post
Hello jaglovers,
about my V12 Daimler double six 1979 series III; D jetronic
I have a low voltage at the coil + VE (3.4 V instead of the workshop ref.value (4-6 V) ( distributor pick-up connector R B Y disconnected)
In order to find the cause, I have followed the white wire at the entry of the ballast resistor and could measure a value of 10V there. After the key contact (white wire at pin 3 inside the car after the key lock) I measure 10.9 (with Key on) (KO: batt=12.7). So I have a (corrosion) resistance in the lock contact which I will try to clean. Anybody has tip on how to proceed?
On the other hand having 10.9 V at the middle entry of the ballast resistors (ign. on), but from there to the coil +Ve I am loosing a lot (10.9 - 3.4= ...) over the resistors, which is a lot. I guess to much. Anybody an idea?
In the workshop manual one mentions an "ignition protection relay"; what are the parameters here? Thanks fr your tips
I forgot to mention the resistor values in the ballast (from top to down):
100 ; 10.4 ; 0.8 ; 1 ohm.
 
  #3  
Old 09-17-2014, 09:31 PM
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That electrical section of the ignition switch is easily rejuvinated.

It is held to the mechanical section with a TINY, Philips head screw, and that is more "felt" than seen. It is around the outer circumference and goes in from the side, usually on the bottom edge at about 7 o'clock for RHD. Once out of the car, it is simple enough to open up and clean. I usually open it INSIDE a clear plastic bag, as there is a small pawl and spring inside that almost always stays in place, but if it flys out you will never find it. The switch will still operate without it, but the "lock" to prevent operating the starter unless it returns to OFF first will be lost.

That ballast has been known to give grief over the years, but in all is a good stable unit.

My suggestion is to reinstate the 12v, or closer than you currently have, to the supply side of the ballast, and then work on from there.

I have read about this protection relay, but never found one on a car down here, so maybe its market specific item, dunno.

My issues with voltage drop over all my years has always been related to that electrical section of the ignition switch.
 
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Old 09-18-2014, 04:14 AM
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Thanks for the info on the lock, Francis!
Do you have an idea what path the white wire (power supply after ignition switch) in the middle of the ballast is following; it seems to go to the front of the motor in the middel of the V and I cannot tract it anymore from there. I would have expected it to come from the lock (ignition switch) ?
 
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Old 09-18-2014, 06:32 AM
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That WHITE wire goes DIRECT to the ignition switch. It goes via a few connectors, that are always a worry.

Why it appears to go to the front is a loss to me.

Hopefully someone with a S3 PreHE V12 will drift by with an answer.

My wiring diagrams show it as an IGN feed to all and sundry, which makes sense, but is not an answer.
 
 
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