Author Topic: Series resistance over heating  (Read 5266 times)

AB

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Series resistance over heating
« on: November 23, 2015, 02:03:19 »
I Just installed a rebuilt fuel pump in my 1970 280SL and was running it for a few minutes to test fuel circulation.  What I believe is the series resistance, that is located on the left of the engine compartment under the bonnet restraining strap, got very hot.  Does this resistor normally run very hot or could it be that I did not start the engine while running the fuel pump caused it to overheat?

1970 280SL, Anthracite Grey Metallic, Light Grey Metallic Top
Shed fined not run in ten years.  Acquired in Oct 2015

450sl

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Re: Series resistance over heating
« Reply #1 on: November 23, 2015, 08:40:23 »
The resistors eat energy to protect your coil...

AB

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Re: Series resistance over heating
« Reply #2 on: November 23, 2015, 16:06:49 »
Thanks for the reply.  This is a new car to me and it looks like someone removed the 0.6 Ohm series resistor and have both leads going through the 0.4 Ohm series resistor.  No wonder it is overheating.  My original wiring diagram does not list two resistors.  I will replace the resistor but do you think it is safe with the one?
1970 280SL, Anthracite Grey Metallic, Light Grey Metallic Top
Shed fined not run in ten years.  Acquired in Oct 2015

450sl

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Re: Series resistance over heating
« Reply #3 on: November 24, 2015, 08:16:59 »
Miner is a 1970er  like yours, and had the MB electronic ignitionbox and although being a very sturdy device , its still 45 years old.
You should be fine with the 0.4er for now , but on the long term you might consider a 123ignition (this is approx 400USD), does not need resistors , and your
car loves it....