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Overdrive help/advice please


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Im trying to sort out an O/D problem on my friends 4A, its fitted with a J type box, so far Ive checked all of the wiring and there is power everywhere there should be, the solenoid can be felt to click when the switch is operated but the O/D will not pull in mechanically, however, if I run the car and operate the solenoid direct from another battery, the O/D does pull in?

 

Looking at the relay with a meter, I get 12 v into it and 12v out of it at W2 .......BUT! If I attach a test lamp .....its bright at C1 etc but very dim at W2 even though the meter reads 12v and also dim at the supply end on the switch

 

My gut feeling is a bad earth somewhere which is where I will go next but and advice would be very welcome

 

Many thanks

 

 

Tom

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Hi Roger

 

Thanks for that but everything is new, the car was fully restored last year, the O/D has worked intermittently, only just got round to looking at it

 

Tom

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Not sure about the tests you have done Tom. W2 goes to the interlock switches so a test lamp will be dim there because power has to come through the relay coil first. You need to do that test on C2 which is the terminal that drives the o/d solenoid.

 

If the lamp is dim on C2 (with the o/d on) there is either something wrong with the connection as Roger says, or the relay contacts are not making properly. If its OK there, try the lamp on the solenoid end of the wire.

Edited by RobH
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A meter may show continuity but its no guarantee the connection can handle a high current (a meter only takes microamps). If you can measure what voltage gets to the solenoid end when the power is applied to it and with the solenoid in circuit it might tell you something about the connection. Is it the same as the voltage you applied direct from a battery ? If not then that is likely your problem.

 

 

I suppose it could also be that the solenoid adjustment is marginal and just needs a wee bit more voltage to make it operate than the car wiring will allow. Have you checked the solenoid adjustment?

 

(edited- of course the J doesn't need adjustment)

Edited by RobH
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W2 is only the earthy side of the relay coil. There is no point in measuring that since the relay is operating OK. The terminal that feeds the solenoid is C2.

 

This is the circuit in case you don't have it:

 

 

post-7865-0-01769600-1515801163_thumb.jpg

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Well Tom could do that Peter, though it sounds as though its not his car. It would involve some wiring changes to put the switches in series with the solenoid rather than to earth as at present (assuming the wiring is stock '4A.) Unless the relay is at fault, doing that its probably not going to solve the problem.

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