72 TA : New Project

[njsteve]

I have a question on that ballast resistor. When you apply 12 volts to one end, what does the voltage read at the other end? I was getting the exact same voltage (12 volts) out of all of the spare ballast resistors I have in the shop. I thought it is supposed to read a lower voltage or am I mistaken?

[John Brown]

A resistor only cuts down the voltage when the car is running. Its like having a restriction in a water pipe. When the system isn't flowing you have full pressure. It's when you open the valve that the restriction effects the flow.

[njsteve]

Interesting! I will do some more experimenting tomorrow and see what the results are.

[njsteve]

Today's experiment involved taking the original resistor wire lead from the original burned factory harness and connecting it between the pos terminal on the coil and the pos harness leads to see if the voltage would be reduced. I would note that the original resistor wire does feel different than the alleged resistor wire that is in the repro harness. The original wire is a much stiffer, silver colored wire with a rubberized jacketing and, not copper wire with regular colored insulation as in the repro harness.

With the car running, the voltage varied between 10.5 to 11 volts depending upon idle speed. With the car off but the key in the run position, it shows 12 volts (as predicted by member John Brown). Very interesting result since it indicates that the original factory resistor wire doesn't cut the voltage down to the recommended 9 volts.

I then took an old ballast resistor, (actually the one from the original cobbled together and toasted harness with the aftermarket electronic ignition) and connected that between the pos coil terminal and the repro harness pos leads. The result was 9 volts when the engine was running and 12 volts with the engine off and the key in the run position. Though not stock, it brings the car right into spec for points ignition running voltage.

I then removed the ballast resistor and hooked the repro harness back up as it was originally and it read 14.3 volts with the car at high idle. When not running but key in run position it read 12.4 volts.

The battery by the way read 12.8 volts with the car off.
When running and the alternator charging, the battery read 14.3 volts, the same voltage as the alternator output. If you shut off the car, unplug the alternator and restart the car the pos coil voltage reads 12.4 volts.

So the inevitable conclusion is that there is no resistor wire in the repro harness and that whatever voltage the alternator is putting out is the voltage that is going to the pos lead on the coil, resulting in fried points.

I will update this electrical mystery after I talk to American Autowire and M&H on Monday.

[mockingbird812]

Good stuff Mac. Good luck and keep us posted! [img]<<GRAEMLIN_URL>>/biggthumpup.gif[/img]

[njsteve]

Just to be safe, I temporarily installed that ballast resistor between the factory pos leads and the pos terminal on the coil. I mounted the ballast low on the firewall using the existing through bolt from one of the three pedal bracket bolts coming through the firewall. You can't see it unless you are really looking for it. Runs 9.4 volts at idle.

[njsteve]

Spoke with both M&amp;H and American Autowire today.

American Autowire is working on getting me a replacement harness. They said it is possible that it was put together wrong, without a resistor wire, a few years ago when I originally purchased it. (Luckily I saved the invoice) They seem to be very attentive to customer needs and it looks like they are going to send me a new harness so I can swap it out and return the old one so they can dissect it.

M&amp;H, the makers of the SE breakerless conversion indicated that you should only run the lower voltage (9 volts) to their unit when running and not a full 12 volt load because it will eventually burn out the unit. They agreed that running the ballast resistor is a good thing to do for the time being.

[mockingbird812]

Now you're gettin' somewhere!

[njsteve]

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: mockingbird812</div><div class="ubbcode-body">Now you're gettin' somewhere! </div></div>

Yeah, it's like a bad 1950's detective novel: [img]<<GRAEMLIN_URL>>/grin.gif[/img]

&quot;There she was, pumpin out a turgid twelve volts, way over my nine volt limit. I said Baby Cakes, you gotta lower that voltage or we're both gonna get burned. She just smirked in the blue afterglow of her tesla-coil, sparks flying like Frankenstein's monster tied down to the slab.&quot;

Hopefully we'll be getting to the good part soon! [img]<<GRAEMLIN_URL>>/rolleyes.gif[/img]

Update: American Autowire fedexed the replacement harness out today. Since they are in NJ, it should be here tomorrow or Wednesday. Then comes the disassembly fun to remove the old one. A+ customer service!

Here's their website: www.americanautowire.com

[mockingbird812]

[img]<<GRAEMLIN_URL>>/haha.gif[/img] You've got a future Mac!!! I love your &quot;prose&quot;!!! [img]<<GRAEMLIN_URL>>/haha.gif[/img]