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Guest Message by DevFuse

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Electrical improvements for Ignition Switch

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#1 Hendrik


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  • Holland and Brazil

Posted 04 July 2005 - 05:42 AM

Dear Moderator(s) ,
This Thread is supposed to be published as a technical Article !
named :

"Improvement of Ignition Switch circuits"

The modifications as listed below where carried out on my 1800 Turbo 4WD 3ATM Wagon 1986.

No garantee can be given that it also works for your Subaru !


From the moment I bought the car , I was disturbed by the flickering of the (digital) dash lights ,
during the time the turning lights where switched on.

Somewhat later the startermotor did sometimes just "click" , no rotation........This was of course critical.


First thing I did was measuring the internal resistance of the Ignition switch :
I measured values between 2 and 4 Ohms (for run ,accessories and start)which is in my opinion a very high value ,
and about 10 times too high , it should be very close to 0 Ohm.........may be in the order of max 0,1 Ohm.
It was measured directly at the soldering points of the switch.

Even if the "big" consumers like rear defrogging ,lights et, are already switched via relays , there is still some high currents flowing via the ignition switch , like radiator fan , turning lights ,wipers , back light(s)
startmotor coil , radio , IG Coil , ECU and some more.

In total it might be well in exess of 10 Amps....in "run" for the IG terminal.
The radiator fan alone , takes already 6 Amps via the Accessories terminal.
Just make your simple Ohmic calculations of R x I , ans you will find unacceptable losses........
and much less power at the application.

Of course the one I have is rather old , but I doubt if in this miniature IG switch there is place available
for better heavy-duty contacts......So a new switch might might behave after a short time as before.

I also did see some questions in the forum from people with variation
of the sound for the fuel pump in combination with the turning lights. (not my case)
Again , probably electrical losses....


I took a simple 30 Amp relais (2 $...) to take over the main current flow for IG
in the Ignition Switch.
These relays have a very low resistance. (in the order of 0,05 Ohms)

I cut the IG lead , on the harness side of the intermediate IG switch connector.
The "using" side of the IG wire is connected to contact nr 30 of the relay.
An extra piece of wire is soldered to the wire of the "B" terminal and connected to nr 87 of the relay.
Both with thick pieces of wire ; soldering still is the most reliable way of electrical connections.
Of course well isolated (here with self extracting material)

The relay coil itself is activated by the original IG terminal.

I found some room to mecanically mount the relay under the steering column.


To take of the electrical load for the radiator-fan via the accessories terminal
of the IG switch , again the same type of relay was used.
The radiator thermo switch now controls only the coil of the relais.
Originally there is a (yellow)wire which is connected to signal the ECU that the fan turns ,
now connected to the relay coil.

From the driver seat you can switch the fan manually on and there is an indicator lamp.
This might help to cool down better at high temperatures and e.g. mountain driving.
An extra wire with additional 20 A fuse goes directly to the battery.


For the starter motor : the same thing.


For the horns I also used a relay to minimise losses there as well.


Some of the modifications are not new ,I guess the Ignition "Bridge" is unique.
All together it helps the oldie is still going strong......

The circuit diagrams are not very nice , made by hand , I hope it clarifies nevertheless.......
I hope this is a usefull number of modifications .
Success !

Attached Files

  • Attached File  ign.jpg   26.87K   253 downloads
  • Attached File  fan.jpg   21.58K   172 downloads

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