Tuesday 8 March 2016

Relays Revisited

When I first checked out the relays there were lots of questions left outstanding.   Since working on the lambda sensor change I have managed to answer most of them.   The original post is here, with the changes in Red.   Here are the specific updates:

 The 2 relays on the left appeared to be 2 of the 3 relays I could not find (ECU, Lambda & Fuel Pump).   While writing my software analysis program I found a way of testing the fuel pump relay while the engine was off.  And by holding it I was able to confirm that the one on the Right was the Fuel Pump.

Also, I had previously found that removing the one on the left stopped the Fuel Pump working so I think we can safely say that one is the main ECU relay as the first thing the ECU does when you turn on the ignition is prime the fuel pump for 2 seconds.

And it turns out the Lambda system relay actually controls the Sensor heater, not the sensor itself, as the heater is not switched on until the engine actually starts.   So removing it would not stop the Fuel Pump from priming.   The only problem is that I have absolutely no idea where it is in the car.   It must be well hidden.

And I have since been told that there are no headlight relays fitted to the car.  I find this odd, as the headlights are quite old and must have quite a heavy current drain and if there are no relays then all that current must go through the light switch.

So now just 2 outstanding questions:

1.  Where is the Lambda heater relay ? 
2.   Are there actually no Headlight relays ?


  1. Do you have any relays behind the switches on the dash? I definetly have a relay or 2 there - can't remember which ones!

  2. I can only assume the Lambda Sensor heater replay is there as I can't find it anywhere else. Next major project is to pull out the instrument cluster so hopefully I will find it. And I have been told the Suoperspec doesn't have headlight replays, which seems a bit odd.