So tried to start my 78 512bb after a while. Tried to get her running and no fire at all. Pulled plug wires on both banks and no spark. So here is where I need some help. Checked power coming to the coil (MSD8202), we have it but don't have it down stream. There is a thick plug type wire out of the back of the coil and there is power there. It plugs into a long heatsync looking thing (ballast resistor I think but it is not the MSD one) with black and green wire coming from the end of that. We tested the green wire with ignition on and did not see any voltage. So is it as simple as something is shorted or broken in that piece? We traced those wires and those are spliced into an aftermarket ignition box (MSD type). But why the 2 wires green and black out of the coil?
I had pulled the center wire off the distributor to check voltage and just had not put it back on. The main wire can be seen in the second picture. So if you can see the green and black wires exiting the left side (first pic), they run down to this MSD through the little block seen in the second picture.
That seems a very unusual set-up where you have something (on the engine or inside the distributor) triggering the red coil, whose secondary high voltage output is "converted" (by that odd long thing with green & black wire) to a low voltage signal to trigger the blue Jacobs ECU box, that then fires the blue Ultra-coil coil which sends its secondary high voltage output to the distributor. IMO, you'd be better off, reliability-and-anti-kluge-wise, getting a more conventional MSD system using only one coil. Can't recall any particular thread showing such a cleaner MSD system installation on a BB512(i), but I'm sure that some of the BB512(i) owners will know of some examples.
I pulled the distributor cap first, cleaned the points, then started checking why we had no fire. That led me to the coil. We are getting power to the coil, just not down stream past the slim block thing resisitor on the fender well. That is why I was asking what it was and if it could cause the problem. Of course the main dist wire was connected!!
You can't measure for this with a DC multimeter -- you'd need an oscilloscope-type meter. If it was working, the signal coming out of the top of the red coil would be a very high voltage spike, and the signal on the green and black wires would be a low voltage spike (used to trigger the Jacobs ECU box).
Points? Are you saying that someone modified your distributor to use points, or installed a different distributor? Don't all the BB (even 365BB) use Dinoplex?
This screwed up system was working ok, just not working now. Would like to fix if possible before putting a real MSD on. So can anyone identify this???? Image Unavailable, Please Login
That is a Jacobs CDI ignition from the early eigthies with a Jacobs Secondary Trigger adapter, but the setup is a bit bizarre indeed. Steve is right, you might want to clean this up and install new MSD or Crane CDI's if the original Marelli AEC104 Dinoplex setup is not there anymore. Here is the wiring setup for an MSD setup: http://www.dinoplex.org/PDF/Wiring_MSD6AL2_for_AEC104.pdf Good luck, Adrian
so it gets more confusing! The dinoplex is still there and hooked up. So I really don't know how the whole thing is wired up. Does anyone have a good set of pictures of a MSD install in the rear of car with pics also showing the wiring harness changes? I assume the harness is disconnected from the dinoplex and rerouted?
The Dinoplex is what's running your red coil. The (excellent) pdf that Adrian posted is really all you (or a shop) need(s) -- the 6-pin connector shown in the pdf is the connector connected to the Dinoplex unit. Try a search on "MSD Dinoplex" -- should get you a lot of 512BB(i) threads (and maybe some 246 threads that you can ignore).
