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Lucas sb316 starter solenoid


BobP
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I have just bought a new Lucas starter solenoid sb316.it only has one small blade connector I assume for the red/white trigger wire from the starter switch.where does the wire from the coil go?. Help please thanks,this is on a spitfire 1500

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If you mean SRB316, the round one with a rubber button, then it's the wrong solenoid for your car. That's the part fitted to early (round tail) Spitfires which didn't have a ballast resistor and hence no connection from solenoid to coil.

I believe the later type, square one with extra lucar terminal, is actually cheaper

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if I remember the early square ones had a little black push button, knowing that I modified the later square ones by drilling a small hole in the raised (boss) plastic & fitting a small plastic rod into it which I can push to remotely operate the starter.

Being an Yorkshireman dragged up in Australia I was taught "Where there's a will there's a way'.

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You can fit the early type - just don't connect the coil wire - but you'll lose the purpose of the ballast resistor wire. You could convert the ignition system to early spec - change the coil to a 3 ohm one and connect a bit of proper non-resistive wire from the white "switched live" circuit to the coil positive - but there's little benefit in that unless your ballast wire is failing. Or you could send the wrong solenoid back to the ignorant supplier (who undoubtedly won't pay any attention at all to being informed of their error), buy the correct one and mod it as Peter suggests.

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1 hour ago, Pete Lewis said:

you can simply fit the ballast yellow /white  coil feed ballast bypass to the starter terminal on the solenoid with an eyelet rather than the lucar 

both are common terminals  it just there to boost the  6v coil with 12v when cranking .

Pete

Thanks a lot Pete will try that

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12 hours ago, Peter Truman said:

if I remember the early square ones had a little black push button, knowing that I modified the later square ones by drilling a small hole in the raised (boss) plastic & fitting a small plastic rod into it which I can push to remotely operate the starter.

The ones with the red button were the push-starter versions, I gave one away by mistake a few years back and regretted it ever since. It's very handy being able to turn the engine over from the engine bay. One on eBay at present but £30 used and £15 postage.

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3 hours ago, Pete Lewis said:

you can simply fit the ballast yellow /white  coil feed ballast bypass to the starter terminal on the solenoid with an eyelet rather than the lucar 

both are common terminals  it just there to boost the  6v coil with 12v when cranking .

I don't believe that's true. In fact, I'm sure it's badly wrong.

If you connect the coil to the battery feed stud then you permanently wire your ignition on

If you connect the coil to the starter motor stud then you short your coil +ve (ballast) to ground through the much lower impedance starter motor, and the engine will not run

If you connect it to the lucar with the switch then the ballast resistor is trying to engage the starter motor

All three options are highly undesirable

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I see your logic  , odd as far as ive seen all early versions were joined with an eyelet on the starter post  not a link to the red /whites ign switch feed early sols did not have the extra/spare lucar to use on a ballast feed .

never the battery feed ( where did that come from) , not studied the diagrams  but there s history here somewhere  maybe 

the later design was obviously better .

Pete

 

  

 

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3 hours ago, Pete Lewis said:

so to correct the logic   if you dont have the extra lucar blade   the yellow /white? ballast boost must be connected to the white /red ignition feed

I don't think that quite works either, as the ignition feed to the coil (through the ballast) is then trying to energise the starter solenoid all the time. If you don't have the extra terminal you can't use the ballast bypass - either leave it unconnected or fully convert to non-ballast.

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to clear up all the thougts on this  I dug out my  lucas manuals it  shows the ballast as being connected via/to the main contact bridge plate 

so it is only energised when the sol is in operation 

then Robs thoughts on alien feeds and connections being un wanted is good and its  ballast feed only powered up when energised 

there  is no way of improvising   correctly any 3 terminal solenoid 

Pete

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