Thread: Amateur auto electrician needs advice

Originally Posted by shack

With that setup the engine will only run will you are cranking, as soon as you let go of the key, power is cut to the coil.

Secondly you are supplying the coil with 9v and 12v at the same time with the engine cranking. The 87 and 87A outlets on the relay are the same outlets.

You need to run 12v on a separate circuit at start, then drop to only the 9v when running.

Not if he is using a change over relay as terminals 30 and 87a are closed at rest.
Best to check out your startermotor solenoid. If it has two small terminals opposite one another, your resistor bypass is already there for you.

Originally Posted by Alpal

I appreciate everyone helping, Is what I need and why i asked. This section or your post is hard to get my head around.{across pins 87-87a wire a resistor with between .8 and 1.4 ohms (lots of vairables here) rated for a constant 10-15w.}

I edited the post and will again until it is correct [I hope].

if you look at your diagram, you have 2 wires running from the relay to the coil, you only need one wire.

if you put your ballast resister across the switching pins of the relay when the relay is in the normal position power will go from pin 30 to pin 87a (normally closed) through the resistor to pin 87 and then to the coil.

when the relay is energized power will go from pin 30 to pin 87 and straight to the coil. Power will also be present at the resistor from the connection to the 87 terminal and flow to pin 87a but its now not connected to anything on that pin.

This makes for less wiring confusion in the engine bay/behind the dash.



a resistor has 3 primary values.. The maximum voltage it can handle(usually set by its insulation), the ohms rating and the total amount of power it can dissipate.(usually related to its construction)

You can safely ignore voltage in this instance as no resistor you're going to get your hands on that can do the job will have a voltage rating lower than the nominal 12v you want to put through it.

The ohms is relevent to its overal resistance and influences how much power it will soak up its important because you need it to drop between 3 and 5 volts to keep your coil running at 9v remembering that your battery will be supplying between say 11v and 12.5 v immediately after the start (too big a resistance at this point and the ignition will cut out from low voltage) and 12.5 to 14.4 v when the alternator takes over and is charging the battery and running the vehicle electrics (to low a resistance at this point may allow your coil to overheat)

Ohms and volts dictate how much power the resistor needs to disipate, in the simplest version, if the resistor is not rated for the amount of power you're asking it to turn into heat it will burn out go open circuit and that kills the ignition circuit. your engine will then try to run when you're cranking it and stop as soon as you release the starter signal voltage.

But as per the elms post, for a 2.25 petrol so long as it has either the correct type of solenoid there will be a connection on the solenoid that is only powered when the contactor is closed (although in my experience sometimes it doesnt work as the contactin the solenoid is stuffed) if you have that you can completely disregard the wiring setup you're looking at in this thread, instead do this.

1. if you dont already have a ballast resistor in the ignition circuit place on inline between the ignition wire to the coil and the coil.
2. run another wire directly from the coil to the afore mentioned terminal on the start solenoid

BUT....

check your coil and the condensor in the distributor first. you may find that these are rated for 12v already which means... you dont need the ballast resistor in the system.

BUT....

check your coil and the condensor in the distributor first. you may find that these are rated for 12v already which means... you dont need the ballast resistor in the system.[/QUOTE]
I hope you are correct. The Vehicle arrived with the coil mounted and the balast resistor attatched to it, I assumed the balast resistor needed connecting. I can only hope balast resistor is not needed. I took it off for the pic and will remove the offending bit and throw it at the neighbours barking dog.