Electrical on street/ strip car

On the car I am building for Drag Week I plan on using
most of the stock wiring harnesses but with relays...
I'll trigger the relays with the wire that normally
would go to the item(in a lot of the cases) sure I'll
need to add some

Stock harness on mine.

Doug,
Interesting question, and one I'll be tackling soon!! When I bought my 62 Valiant, it was a bracket car, with moroso W/P drive, no alternator, Mp ignition, and started with the key.
My plan all along was to put it back to street/strip, but I was in a hurry to go racing! So I added a painless wiring 6 switch panel, relays, and a digital 6, and completely bypassed the stock system...
Now, I want to get the lights hooked up, alternator hooked up, and I'm trying to decide how much of the 50 year old stock harness to trust, and integrate into the plan...

if it were me I would eliminate the old wiring harness and use just the switches and key. thats pretty much what I did on my challenger. except I didn't use the key. but I used the overhead roll bar mounted switch panel. could have easily used factory switches. mine is wired for turn signals, lights, brake lights etc. painless kit

I use the stock harness for lights and wipers only. Everything else is worked off of a relay panel I built in the glove box, switches are on my TA shifter console. It does use the ignition switch still.

I thought it would be cheaper to build my own relay panel. By the time I was done I could have purchased one for just a small amount more.

IMHO..I think it's far easier and that you'd be way ahead using an aftermarket kit.There are several to choose from and lots of good ideas in the street rod magazines.

how much of the 50 year old stock harness to trust

Definitely, replace or bypass all the original bulkhead connectors.

Either way I will buy all new. Its not about the cost. I only have one chance of doing it right. I am thinking about complete aftermarket so I can hide most of the wiring.What kits have you used and how were they?

Doug