I installed a 70 amp alt and a HEI dizzy in my 79 f150 and now the motor wont start. I put a new battery and voltage regulator on also. I show 13.26 volts at the battery with the ignition off but when trying to start the truck I show only 9.36 volts to the ignition wire for my Dizzy and it requires a full 12v. Anyone have a cure for this problem? Thanks

 

The voltage is cut back at the solenoid when the engine starts. It shoud have full battery when cranking.

 

I thought it would but when cranking Im only getting 9 volts to my dizzy wire But when im not cranking i get 12 volts to the wire with the ignition on and not cranking.

 

It sounds to me like the wire you have going to your distributor was originally intended to go to the coil and either has a ballast resistor inline or is a "resistor wire" which intentionally cuts the voltage down to your stock coil

Edit - probably not so if you're getting 12 volts when you're not cranking. It is very possible that you just have a voltage drop problem due to poor connections, load on the wire, too small a wire, etc. What is your actual battery voltage when cranking?

 

I have a 12 awg wire that is ran directly from my dizzy to my ignition wire. I also had to lenghten my wire from my alt. to the solenoid and regulator. for the bat. wire I used 10 awg and for the sta and fld wires I used 12 awg. Could be poor connection cause I just had everything wire temporary cause I only have a rolling chassis right now.

 

Electricity can be a funny thing. A given length of wire tends to have a certain resistance which will cause some amount of voltage drop. The longer the wire the higher the resistance and thus the higher the voltage drop. As a device tries to draw power, across a wire, as the voltage goes down, the current goes up. As the current goes up so does the heat in the wire. As the wire gets hotter, it's resistance typically increases. The increase in resistance decreases voltage more, which increases current more, etc. Eventually this can lead to your wire getting so hot that it melts the insulation, melts itself, etc.

As such I always try to run the largest gauge wire that is feasible for my application and keep the wire runs as short and neat as possible. #12 copper wire is supposed to be good for around 20 amps. I seriously doubt that your ignition draws anywhere near 20 amps so if you are having a voltage drop, it is likely not because of the wire, provided that the wire length is not excessive and it's not seriously kinked, broken, frayed, etc. This means you should double check all of your connections. If you have to splice two connections use very good quality crimp connectors. It is better to crimp AND solder them, and make sure that you properly insulate the splice. NEVER just put bare wire under a screw head. Always use a quality crimp on lug with a ring terminal and make sure your connections are tight and corrosion free. Some people will argue that it's a pain in the *** to do the wiring properly, but I will argue that it's a bigger pain in the *** not to. If you take the time to do your wiring correctly, you will instantly eliminate one source of trouble for good.

As far as your alternator wire, I would seriously consider an upgrade. You have a 70 amp alternator but you ran #10 wire which is rated for 30 amps. Now you could PROBABLY get away with it because it's not likely that your alternator will ever have to put out it's maximum 70 amps solely across that wire, but why risk it? If you do you're gonna be looking at some serious heat, voltage drop, and fire hazard issues. #6 wire is rated for 75 amps and would be a MUCH better choice. You can usually buy larger wire sizes by the foot at your local hardware store. Buy just a little bit more than what you need and you'll find the cost to be very reasonable. Also be sure to use heavy duty crimp on insulated lugs and do yourself a favor and get the proper crimping tool for the lugs you are using.

Once you do all of your wiring properly you SHOULD find that the voltage going to your distributor while cranking is very close to the battery voltage while cranking. If this is still in the 9's, it's very possible that it is entirely too low to fire your HEI ignition. I believe that typically you do not want battery voltage to drop below 10 while cranking. So, get your meter and check. Is your distributor voltage significantly lower than battery voltage while cranking? If so then you need to improve your wiring layout. If not, maybe your battery doesn't quite have the juice needed to crank it AND fire your HEI.

Good luck!

 

Nathan, I certainly appreciate all the info, I will make sure i put a heavier wire for my alt/bat wire. I was trying to run my alt wire down under the motor so the top of the engine is clean but that may be causing to fasr a run and losing voltafge due to the length. I appreciate all the help.

 

If you need extra length for routing, just compensate by using the next bigger size wire. However, I doubt your alternator wire is your starting issue, as it should start without an alternator even hooked up. The #10 wire may cause issues later, but I don't think it's causing this issue.

 

As Nathan mentioned, you might have the ignition module in the distributor sourced downstream of the factory ballast which is part of the wiring harness. If you've got your coil and ignition module tied at the same point, the current draw of the coil primary winding will knock down the voltage to the module and it may not be able to turn on. As such, you do not want to use the original coil power wire to power an aftermarket ignition module with a Duraspark setup if your new module is calling for 12 volts. However, as Mark mentioned, the ballast should be bypassed during cranking, so this is normally only a concern when the engine is running (key turned to RUN). There might be some funky wiring business going on.

Also, check the voltage across your battery terminals while the engine is cranking, and compare it to what you're seeing at the distributor. The voltage will sag some during cranking as the starter current drops across the battery's internal resistance. You need to look at the source voltage during cranking too - at this point you have no way of knowing if the voltage at your distributor is dropping because of a resistance wire, or because the battery voltage is actually dropping (which is to be expected to some degree).

 

K thanks. I think im just not getting enough volts to my dizzy to start the motor I will have to play with it more and seee what I got.

 

Ford Ignitions run on 7-9 volts

What you have is normal.

You may have to find another keyed 12 volts (behind cluster Yellow 3-way connector)
or a 12 v source under the hood (keyed power).

 

My dizzy has an internal coil that only take 1 12awg wire from a 12v power source. soea away with my coil and module. I have it ran to the factory wire that fed my module and I have doe away with my factory dizzy and coil wore harness.

 

In that case, move on to check the battery voltage while the engine is cranking.

 

His HEI dizzy uses a GM 4 pin IGN module, I have one on my truck.
The 4 pin module DOES NOT conduct current with the key ON and engine not turning. Thus no current flow across the resistor wire and thus no voltage drop across it.
So 12v key on and 9 volts while cranking is normal in his case.

 

If you used the coil positive wire as a power source to feed the new DIZZY you would be downstream of the resistor wire.
But if you used the power source for the DS2 module it would be a clean power source, but not really a good high amp power source. You could use this source to power a relay.
It should have spark at 9 volts, but just move the power wire to the battery + for trouble shooting.
Are you sure the DIZZY is not 180 deg out?
Jim