8 replies to this topic

[Marks LXTorana]

Hi all, I have an electrical gremlin when trying to start my freshly built engine (304 block with Holley carby). It wants to run when I'm cranking it although when I stop cranking the engine dies. Keep the ignition in the cranking position and the engine runs. I thought maybe the live wire to the coil was possible dead in the "run" position although the voltmeter confirms I have 12 volts.

Is the attached diagram correct for my set up? The only thing I can think of is that I have an extra earth wire that is grounding the ignition signal to the distributor in the run position, which I will check tonight. My tachometer signal wire currently comes off the coil although I will change it over to the grey wire so I can program the rev limiter.

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[Dr Terry]

If you are using the factory yellow wire to supply 12V to the coil, this is your problem. The yellow wire is supplied thru a ballast resistor which is built into the harness. What this means is that the 12V that you a seeing on the voltmeter is not a good 12V, because it's not under load.

 

Do 2 things first.

1. Re-run your tacho wire to the MSD's grey (gray ?) wire.

2. Temporarily run 12V directly from the battery & then try to start.

 

The engine should start immediately. If it does run a new 12V supply wire from the ignition switch which has a full load 12V for both start & run.

 

A simple wiring trick is to drop the steering column & short the yellow & (thick) pink wires together. This will give you a good 12V supply in both these positions.

 

Dr Terry

[Marks LXTorana]

Spot on Dr Terry as always!

I rewired the tacho to the "grey" wire and ran a temporary live from the alternator to the coil. Started first time!

 

Now my confusion lies with your permanent fix. The original wiring diagram shows the yellow and pink wires from the ignition already joined before the yellow then extends to the coil. I can recall seeing the yellow and pink wire joined in my car which made identification much easier. Are you saying there is another wire to join with these? I have to say it doesn't seem to show any ballast, unless it is reflected by a slight squiggle in the pink wire going to the fuses?

[76lxhatch]

Its a matter of which end they are joined at, because the thick pink wire itself is the ballast resistor (resistance wire). You need to join them at the steering column end as mentioned.

[Dr Terry]

This is why I said "thick pink wire". The ballast wire is actually cloth covered & is thinner when compared to the thick pink wire which supplies 12V to the fuse box. The thick pink & the ballast wire are joined together at the IGN 1 terminal of the ignition switch.

 

This thicker pink wire is regular copper, as is the yellow wire so they can be easily soldered to each other. The ballast wire is 'ni-chrome' & will not take to solder easily.

 

There are many different ways of achieving a full 12V supply to the ignition coil, but I've found this is the simplest & most reliable. It is also easily reversible. Just shave a bit of plastic insulation off each wire & solder them together. Don't cut any wires.

 

Dr Terry

[Marks LXTorana]

Perfect, thanks guys. Not only do you have the solution but also a very simple explanation as to why!

I'll get onto it today and report back.

[Marks LXTorana]

Done! The wiring took no more than 15 minutes and it started first go. She is purring like a kitten (actually more like an angry lion!).

Thanks Dr Terry and 76LXHatch for your help.

[76lxhatch]

The ballast wire is actually cloth covered ... <snip> ... thicker pink wire is regular copper

Interesting, all the ones I've seen appear to be insulated with regular plastic (or whatever it actually is) and are printed with something like "resistance wire do not cut". Perhaps that is later models though, and you don't see many unmodified these days.

[Dr Terry]

Interesting, all the ones I've seen appear to be insulated with regular plastic (or whatever it actually is) and are printed with something like "resistance wire do not cut". Perhaps that is later models though, and you don't see many unmodified these days.

Quite correct. Early cars have a cloth covering & the later cars have a heat-proof plastic covering with the 'do not cut' wording printed on it.

 

Dr Terry