Failed Restart Ignition Resistor

[Phil Gillespie]

So been playing around with ignition system on 39 coupe still 6v +ve earth.
The trail of the Electronic Unit which does away with condenser has not been performing as hoped.
So changed her back to original set up. 3rd Generation 78 model divers helmet distributor with supplied condneser and fitted with an original rebuilt Skip coil.
Still running as per original set up the resistor under dash giving 3.5 to 4 v to coil.
Test run at good load and nil rough running or noted miss as before around 40 to 50 mph.
Got home and into garage stopped engine and Shit it would not restart!!
Condenser??? Then checked voltage after resistor and found only 2.5v no wonder it would not crank up. When it got hot of course increase in resistance.
This resistor was 0.8 ohms initially.
So found the cause of the non start for sure and now to get a reliable resistor.
Thought the resistor I had fitted was a good one.
For a good qualty unit to go to??
Thanks,
Phil NZ

[petehoovie]

"For a good qualty unit to go to??" > Third Gen Automotive....Ideally, you want a NOS resistor....

[koates]

With the distributer timing points closed so that the coil has power on it then check the voltage into the resistor and then out of it. The old ford ignition switches give trouble with bad connections inside. You can bypass the switch to test if its good or not. Remember testing voltages in the coil primary circuit the distributer timing points MUST BE CLOSED so that the coils current draw is loading the circuit. No point testing without the loading on the resistor. And yes use an original FORD RESISTOR if you can because they are the best quality. Regards, Kevin.

[koates]

Phil, your 2.5 volt reading at the coil (engine stopped) may be OK because you are testing with the engine stopped and timing points closed. The longer the ignition is ON while you are testing voltages then the hotter and hotter the resistor will become and hence the lower the voltage becomes. This circuit is all designed to work with the engine running and distributer points rapidly opening and closing which acts as a current limiter. Just fit a new condenser for a trial. They give a lot of trouble . Regards, Kevin.

[Brian]

Back in the old days, the trick was to hold a penny across the resistor to allow full voltage to coil for those hot starts! -useless trivia for you.

[Phil Gillespie]

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Originally Posted by Brian

Back in the old days, the trick was to hold a penny across the resistor to allow full voltage to coil for those hot starts! -useless trivia for you.

Well I did similar after the non start. Put a jumper across the resistor. It started right up. So changed it out with a spare??? Will keep the jumper handy in meantime.
Phil NZ

[Phil Gillespie]

I see on recent posts on similar the use of a 4 pole solenoid to give full voltage for start up and also the use of a diode to give the same full voltage for start up.
I'm using the coil with 0.8 ohms plus the 0.5 ohms resistor and have previously checked when running at idle and get 3.5 A approx which is in the ball park.
Phil NZ

[JSeery]

Originally Posted by Phil Gillespie

I see on recent posts on similar the use of a 4 pole solenoid to give full voltage for start up and also the use of a diode to give the same full voltage for start up.

But you will need to find a solenoid that works on 6v with ground to close it. Or rewire the starter switch to provide power vs ground.

[flatjack9]

I gave up on resistors and use resitance wire. Just have to figure out the length to get the right voltage.

[JM 35 Sedan]

Originally Posted by flatjack9

I gave up on resistors and use resitance wire. Just have to figure out the length to get the right voltage.

Good idea! I've found brand new resistors that were poorly crimped at the ends of the wound wire causing intermittent function in the ignition supply circuit. I've had to silver solder them to make them work in the past.

[Phil Gillespie]

So today took the 39 coupe for a run down to local town and back.
It went well. When I got home into the gargage and turned it off. The restart was as before. Would not start up. Previously had changed out the resistor so maybe not the problem? Have a "trash can" condenser fromTubman on the way.
Presently has me stumped.
Phil NZ

[KGS]

Originally Posted by Phil Gillespie

So today took the 39 coupe for a run down to local town and back.
It went well. When I got home into the gargage and turned it off. The restart was as before. Would not start up. Previously had changed out the resistor so maybe not the problem? Have a "trash can" condenser fromTubman on the way.
Presently has me stumped.
Phil NZ

Maybe a bad, or just dirty ignition switch. I had that problem with my '39 and I had to rebuild the switch.
Ken

[Phil Gillespie]

Originally Posted by KGS

Maybe a bad, or just dirty ignition switch. I had that problem with my '39 and I had to rebuild the switch.
Ken

Have recently rebuilt the ignition switch I did think the same.
Phil NZ

[Phil Gillespie]

This morning out to garage and engine started right up after overnight and cold start. Must be some link as to cold start and hot restart. I'm hoping condenser?
Phil NZ