That is a great idea, I found this pic that looks workable.
Problem is all the new ballast seemed to be completely sealed, not sure how well you could cut that ceramic material, seems brittle?

a deft hand with a dremel type tool should work, with having the ballast clamped in a stationary position, to remove the unneeded ballast. but remember, the duel ballast has two different values, but i can't remember off hand what the resistances are. that is why there are locating pins on the plugs, to index the ballast slot. pick the side with the resistance you need, then gut the other side. hope this makes sense.

primary resistor uses to be between .5 and 1.5 ohms

secondary 5 ohms.

several ppl has got success modifying the ballast ( per an idea I posted once ) to the ballast bypass replacing the resistor with a jumper wire on ceramic groove to those ign system doesn't need the resistor anymore ( such as FBO and some others ). In that way you don't need to hack the wiring and still keep the stock look on firewall, and get it back to stock just replacing the ballast again remaining the wiring untouched. The white stuff is simply epoxy, easy to remove.

now, using a dual ballast in place of the single ballast just to hide the diode, Dunno if will look right a bigger ceramic piece and unused prongs there. Simply wouldn't look right. If you already got a single ballast, is better just install parallel the diode between ballast prongs ( solding or using dual male/ single female spade kind splicers ) and protecting with shrinking tube. I think would be less noticeable than the weird uncomplete bigger ceramic stuff. My idea came on if already using a dual ballast with double plugs on engine harness

thanks for reviving my old memory on the resistance values natcho ! my idea of using the dual ballast was to hide the diode in the unused cavity, then use spades [factory tabs through the ballast] and re-wire the dual plug to connect the single ballast to the diode. it wouldn't look totally factory correct, but similarly correct, as you would be using factory terminals and a factory ballast. i guess it would come down to how the final appearance looked, and it's position on the car. hope i'm somewhat clear in projecting my thoughts on this idea.

yes... could be nice too... One groove with the resistor, the other groove with the diode. Just would need just to jump out on dual ballast plugs on both sides. Blue wire is already done actually from factory on existant dual ballast setups, just would need to jump the brown side between both prongs straight at the same plug like blue wires are already done.



This is of of course you are using a 4 pins ECU, not 5 pins. You would be sacrifing the secondary resistor what feeds the unexistant pin on 4 pins ECUs

and as mentioned ALLWAYS conecting same plugs on same side of ballast, never reversed like being just a resistor doesn't matter.