Voltage Drop to Dizzy When Cranking

[77CVT]

Swapped the points dizzy in my '71 with a HEI.  There is a massive voltage drop in the wire that hooks to the HEI.  I get 12v with ignition on but when cranking it goes to <1v.

This means it won't actually fire until I release the key back to the on position.  I tried hooking a relay with that wire as the switch wire but there it wouldn't trigger the relay when cranking.

I'm sure that this wire was only ever supposed to carry about 8-9v when cranking because of the old ig coil setup, but even 8v I'd be happy with.

- Could it be leaking voltage from the ignition key?
- I'm figuring it may be easier to chase a wire that has enough voltage when cranking (starter wire?) and use that feed for a relay.

Suggestions?

[Vettech]

There would be little diff between std or HEI current draw. Capacitor discharge ign will use very little current, and as long as you turn on ign (hear it run up ) and then crank they will fire everytime, but alas everybody wants HEI. If the wire has  ~1v now, then it was likely it was like thls before you changed it. I recently changed to reduction gear starter, turns an 87 - 350 over like magic. The old starter laboured when RE-starting hot, sounded like it was labouring with a flat battery, but was a combination of stuffed nose bush, heat soak, no shims (incorrect teeth spacing) and age. (possible higher comp in motor- another story). The advantages of HEI are, no point wear, correct dwell angle for all combinations of engine revs ~ load, constant current load thru coil. In all vehicles with older style starter motors, the voltage will drop VERY low when cranking, BUT ~2volt is FAR TOO LOW. Check cables, crimped lug ends, cable diametre, dirty joints/corrosion at battery terminals, and the size and connection of the earthing cable.(this needs to be on the starter to block bolt) In my 78 the battery is in the cab behind the LH seat, the cables are long, I've replaced the originals with good quality welding cable. A good tip is to clean the battery terminals, tighty fit the cables - then give a very (VERY) light spray of "Lanolin". Sorry to prattle on, hope this helps. Oh! sometimes if the starter is poling (I think its called) it will draw far too much juice and act like a short, dropping the battery termimal voltage to nothing.

[Reklaw]

Have you measured the voltage across the battery while cranking? Hasn't got an immobiliser in it has it?
BobW

[sabre]

Original points / Delco distributor used a 9 volt coil and voltage drop resistor either built into the wiring or as a ceramic resistor. During cranking the resistor is bypassed to give a strong spark during cranking. The ignition switch has a separate output to make this happen. Either the bypass wire or the switch will be the problem.
On some other models the same function is provided from the starter solenoid. Try running a wire from the second (normally unused) small terminal on the solenoid to the HE I power terminal. It will supply 12v during cranking. This is standard wiring in some cars and when Chevs are used in boats.

[Vettech]

Good thinking Sabre, I must admit I never gave it a thought that the car could be original, been a while since I've seen an original.

[sirfixalot]

The yellow wire on the starter puts 12 v up to the coil when engine cranks. You should also have a pink & black wire at the coil joined to the yellow. The pink & black wire is the inline resistance between coil & firewall plug on left handside of car there is also a fusable link in series between coil & firewall plug. You need to run a new wire from the fusable link to the coil & bypass the resistance wire.From the firewall plug you have pink & black wire copper - fusable link - pink & black resistance wire - coil

[77CVT]

Thanks gents.  yes it's original, but probably butchered in some places.   

I'll check that sirfixalot and if it frustrates me too much I'll check sabre's idea.

I have a reduction starter on my 85 to Vettech, night and day difference!   

[sabre]

I'll check that sirfixalot and if it frustrates me too much I'll check sabre's idea.

I think you'll find sirfixalot's and my input are the same. Sirfixalot has just added the wire colours and picked up my oversight of removing the dropping resistance.
You'll find the HEI will work with the dropping resistor (either the inbuilt resistive wire or the ceramic after market) but the HEI should have full power so sirfixalot is again correct. It should be removed / bypassed.
Good luck.

[Vettech]

well!.. what happened, how did you go?