Where's the best spot on a 71 to get my 12 volts to trigger my msd box ? its pre wired for my Duraspark dizzy so that part is easy and I know the big red wire go's to pos side of battery and black go's to neg side....
I setup mine the other day. Big red goes to positive. Big black to negative side of battery. Small red to igintion wire on drivers side. Orange wire to positive side of coil. Black to negative side of coil. Magnetic pickup to dizzy if it has it. White to the points/amplifier. Hopw this helps.:Handshake
If you are looking for a good spot run the small red wire off the MSD to power: I just set mine up recently and found that I had an open accessory terminal off of the fuse block. The connection is "switched" meaning it will only come on when the key is turned to the on posistion. It is a single post without anything else associated with it so it returns a full 12 volts. I probed several other connections and found that there was a draw that took the voltage below twelve volts when cranking as other components were being ran off the same wire. The MSD will not trigger properly with low voltage. I passed the wire through the firewall via a OE grommett and then ran the wire forward to the MSD. Seems to work great now. Mike
Thanks Mike, I'll look to see if I have a extra feed on my fuse block.... That would be a good place for it...
I have an ignition/accy relay wired up and ready to install with my new relay bank. Trying to take most of the load out of the cars original harness. Use an existing ignition feed to trigger the relay control side. The load side of the relays run to a Batt + fused feed. This way my ignition feeds and loads are under the hood and the existing old wiring from the ignition switch is for low load relay triggers only. Also relays for horn and headlights. Mounting in the washer bottle since its never been filled. LOL. Best of all I know I have a new, good 12 volt supply. Just thought the relay may be an option for you instead of an old ignition feed.
I haven't worked with relays before, but now is as good a time as any... I will look into wiring in one... I can just mount it next to the msd box right ? Im putting it where the windshield bottle used to be...
Ok im going to bump this thread.... Someone chime in on where to pull 12 volts... Every key on 12V i've tried so far drops below 10V in start mode... If I use a relay with the same sorce the relay will quit working in start mode right ?.. I tried using The accessory stud on the fuse block it also drops below 10V in start mode... HELP !!!
I really don't think it needs to be a full 12 volts. It simply turns the MSD box on and off. I am using my original wire from the coil. As long as the large red wire is getting full battery voltage your ok.
I havn't checked the battery voltage cranking yet... Key on I have 12.75 at the msd... In start mode it drops to around 7 volts on the trigger wire..
The old coil wire is where I tried first... At least I think that was what it was, it's the old harness that also has the temp and oil sending wires as well Right ?
I'm wondering if most of the voltage drop you're seeing with starter running would also show right at the battery.
I'll check it when I get home... If I use a relay to turn on my box, dose it have to have key on 12V or 12V while cranking over the starter ?
I won't comment on that since I don't have personal experience with the ignition boxes. Just chimed in 'cause I thought the voltage drop might be occuring at the battery because of the high current for the starter motor. In which case, you NEVER find a 12V source with the starter running.
