Dist power from ign sw?
 

OK I am trying to start my stock 350 chevy with a new dist I installed----new wiring harness also. I can get it to turn over and occasionally backfire. I have the dist power coming from the far side of the ign switch--start position---wrong? or where does that ign sw. terminal go? and where do I get HEI power? I have lots of unused wires on this new harness TY

Re: Dist power from ign sw?
 

You need constant power. Start position only is powered till you let go of key. Needs to be hooked to run position.
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Re: Dist power from ign sw?
 

Yes, ignition switch has an "S" terminal for start that goes to distributor +.
(It is cast into bake-a-lite plastic back on ignition sw.)
Does it backfire when you let off the key, or during cranking. If during cranking, the distributor has B+, but not on TDC #1 on power stroke. If backfires when you let off key, power to the distributor is coming for on and loaded with gas in cylinders.
Check the search box and check the box for "Forum" and wiring diagrams in color can be found. Many talented Tech's have posted their heart out as it take a lot of work.
I have never purchased an aftermarket harness, but most come with markings on wires. Just because I build my own, you may have extra wires that are not used depending on equipment, year and add-ons.
Let us know of shoot a PM for help.
Retired ASE Master Tech & Ex ACDelco instructor.

Re: Dist power from ign sw?
 

HEI Power is terminal closest to firewall, while the one next to it is tach signal. Just for giggles, remove front drivers-side spark plug and stick a finger loose into hole. With a buddy, use a remote starter / jumper, crank over by "Bumping" to get compression on #1, then look at timing marks. Move with wrench backwards to 10 degrees before TDC or "0", install old spark plug or spark tester into #1 wire. If you supply B+ to HEI, loosen hold down bolt, rotate distributor cap/housing counter-clockwise, then slowly rotate clockwise until you get spark...lock down. You're are 10 degrees before TDC on #1 in power stroke.

CAUTION: Make sure choke valve (Butterfly) on carb is open and throttle is open. This will help keep fuel from building up in the intake & cylinders.

If you did a T-Chain prior to starting with dot on dot, this is 180 degrees out of timing. Common mistake for #1 cylinder in "BANG" stroke!

Remember; the 4 strokes of an engine are; Suck, Squash, Bang, Blow. You want Bang on #1!