I'm looking for advice regarding modifying a perfectly good reproduction engine wiring harness to provide full time 12v to the coil and HEI-type ignition module. If I understand correctly, the stock ignition is set up to provide a full 12v to the coil and points only during cranking. It drops down to about 9v when the ignition switch is allowed to return to the "Run" position. The problem is, even after reviewing my very easy to read Stage 1 Restoration poster size '72 Buick wiring schematic, I'm not absolutely sure which wire by-pass (or un-solder from the splice or terminal at each end) and replace with 14 or 16-ga red or pink wire. I "think" I'll have to R&R the wire that's labeled on the schematic as "20 WHITE/ORN/PPL (1.8 * RES.)" that runs from the firewall receptacle to a splice somewhere before the coil "+" terminal. Does that sound right? As always, thank you in advance for the help.
See this thread: https://www.v8buick.com/index.php?t...ystem-function-tests-and-modification.248990/ As described in the thread, I removed the terminal for the original points wire from the engine harness plug, where is plugs into the back side of the fuse box (the one with the resistance wire spliced into it), and taped it up in the harness. I added this in it's place and just zip tied it to the original harness: https://www.yearone.com/Product/1964-72-skylark-gs/l00510 That red wire connects to the 12V ignition conversion that I have. this way if anyone ever wanted to convert it back to points, the 12V wire can be easily removed and the original resistance wire for the points reinstalled.
Find an unused switched terminal on the fuse box and run a new wire to the HEI. You should be able to hide it pretty well.
I was able to do this on other GM cars I've owned, but this GS400 is very optioned out and the IGN terminal in the fuse box was already occupied by a connector going to the power seat. If the terminal is open, that is a far easier way to provide the 12V source for ignition.
Rich, Just use a relay which will be triggered by the rsistence wire. One wire from a 12volt ignition on source & another going to the HEI. Very simple, easy to do & no messing with the resistence wire at all. IF the time comes to use points again all you have to do is hook-up the resister wire to the coil again. No cutting, splicing or otherwise. Tom T.
Tom, My car was actually set up like that from the previous owner. It was all PerTronix stuff (relay, coil, and module). When I started having issues with the ignition system, I took it out and installed the 12V wire to replace the stock wire in the harness connector. I was trying to simplify things and constantly cleaning the wiring contacts on the relay. Eventually, after replacing everything with another distributor and the FAST electronic conversion, I determined that the ignition problem was actually a worn out distributor.
Recently I learned another thing in relation to this. When installing an electronic ignition conversion system, make sure that when you turn the key to the start position (to engage the starter), there is at least 10V at the coil when cranking. I was having some problems with the ignition firing when starting. Measured 7 to 8 volts when cranking. It turned out to be a weak battery. Now that the battery is new, it fires up every time. I guess the weak battery is not as noticeable with a mini starter.
Maybe a piggyback connector would work. https://www.ebay.com/itm/272676004587?hash=item3f7cc1a2eb:g:eOgAAOSwubFaaYpP
I'll have to check that. I'm pretty sure the power seat only works with the key on. Maybe its the power windows that are plugged into that.
