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Landyfella

Active Member

• Nov 28, 2020

• #1

Hi, I have just received a new Britpart solenoid and the instructions say the battery lead should be on the terminal furthest from the mounting bracket. However on the original/one of car it is the other way around.
So
a. does it matter
b. if it does should I go with the original (car) way around or the instructions.
Picture show new solenoid wired same as original/old one.
Thanks
Chris

 

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rob1miles

Well-Known Member

• Nov 28, 2020

• #2

Instructions if you have a ballast resistor for cold starting as this become live when cranking, if you put it round the wrong way this will always be live.

 

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Webley1991

Well-Known Member

• Nov 29, 2020

• #3

Surely a petrol wouldn't have any need for a ballast resistor, unless I'm missing something?

 

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rob1miles

Well-Known Member

• Nov 29, 2020

• #4

The petrol "may" can have a ballst resistor on the coil for cold starting. The coil is 10V and the ballast is wired in series with the coil to give the coil 10v. A wire goes from the small spade on the solenoid to the coil by-passing the resistor so that when the battery voltage drops to 10v during cranking the coil gets full voltage. Very common on 70s Brittsh vehicles and really helps cold starting. Sometimes the little spade is on a washer and can be swapped over. If you put it on the wrong side the coil is always live. They're are obviously only used on petrol engines and look like this:
https://www.ebay.co.uk/i/3036452696...Z1_jRDf5OJNWpw-xvHWoOa0BAFIx9y_waAiwBEALw_wcB
So to answer you question: yes you are missing something; a petrol does sometimes have a ballast resistor, they were often added along with a 10v coil to improve cold starting, take a close look at the coil voltage and part number to see whether its 10 or 12 v

 

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Webley1991

Well-Known Member

• Nov 29, 2020

• #5

Thanks. As I have only ever owned a diesel Series I am not familiar with the petrol wiring.

 

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Landyfella

Active Member

• Nov 30, 2020

• #6

Is there a way to determine I have wired it correctly?

 

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rob1miles

Well-Known Member

• Dec 2, 2020

• #7

I would put a bulb across the coil to ground and see that you get power when you should. If there are 2 wires to the coil +ve then it probably has a ballast resistor, if there's one then not.

 

TheMegaMan

Well-Known Member

• Dec 2, 2020

• #8

To address point a in the original question, both terminals on the solenoid are equivalent, so it doesn't really matter which terminal goes to the battery, and which to the starter motor. What matters is that you connect any wires that went to one terminal (if there were more than one), to the same (shared) terminal on the new one.

The only argument I can think of for connecting the battery to the terminal furthest from the bracket, is that you're minimising the risk of shorting the battery to the bracket (which will be at ground), should you drop a spanner on it, or something. If you're careful or insulate the terminal, that hopefully shouldn't matter.

 

ExMil109

Active Member

• Dec 2, 2020

• #9

+1 on MegaMan's response. The diagram in the Haynes manual shows the terminal furthest from the bracket as the input from battery, but I don't see that it matters electrically which way round these two terminals are connected.