help i cant get my truck to start

[1972chevyowner]

i have got it down to when i let go of my key i have no spark so its an ignition problem ?? so what do i look for to fix this??

1972 350 and im still running points

any help would be great thanks

[geezer#99]

Check the wires on the starter. Could be yellow one broke off.

[1972chevyowner]

I just put a new starter on and replaced that wire I put a bigger wire on could that have made a difference??
I have spark when the key is turned but not when i let off I thought power was only going though that wire when the key was turned ??
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[geezer#99]

The yellow wire sends 12 volts to the coil in start mode only. If you follow it back to the coil you'll see that it joins with the resistance wire from the ignition switch.
When you replaced it did you make sure it was like original wiring.

[1972chevyowner]

my starter had an S and an R i hooked the R up to the switch it was a purple wire for the S it had a yellow wire hooked up to it the wire was so bad i broke it in half like a twig so i replaced it with a new wire it is a thicker wire its red

at the coil there is that new red wire on one side and on the other side of my coil there is a black wire that goes to the points

i hope this explains things a bit better

[VetteVet]

The red arrows show the wire from the ignition switch to the starter and then to the coil. The white/orange/purple is connected on the inside of the firewall to the ignition switch. It is the resistor wire and I have seen it go direct;y to the positive side of the coil and connect there with the yellow wire from the R terminal on the starter.

[geezer#99]

So if you replaced that yellow wire did you splice it to the resister wire pointed out by the arrow in Vettes diagram? If not it won't stay running when you release the key.

[1972chevyowner]

so if i trace my old yellow wire i will find another wire hooked to it??

i know what you guys are saying is my problem!!

[geezer#99]

Yup. THe yellow wire is connected to the resistance wire.
What the yellow wire does is supply 12 V to the coil only when you start the motor. When the solenoid on the starter gets power thru the purple wire (from the ignition switch) there's a disc in the solenoid that contacts the yellow wire terminal in the solenoid. When you release the key back to run position the disc moves away from the yellow terminal.Then the power to the coil comes from the ignition switch thru the resistance wire. The resistance wire drops the voltage to 6-7 volts. The coil can't run with 12V all the time or it burns up. That's why there's a resistance wire. To drop the voltage.
You need the extra voltage for starting but not while running.

[1972chevyowner]

haha learn somthin new every day i will fix it today and tell you how it goes thanks for all the help

[VetteVet]

If you plan on keeping your truck there are three modifications that you absolutely should do on it.

1 The headlight relay mod.

2. The external to internal voltage regulator alternator mod.

3 The points to HEI distributor mod.

There are many others too but they are rather expensive. You already
have the disc brakes, but the overdrive transmission is a great upgrade.
The Tilt steering column,Power brakes etc.

The first three can be done for under $100 each by almost anyone, even without professional help.

[1972chevyowner]

Well it runs like a beast
And I plan on doing lots of things to it cause I never wanna get rid of it
Thanks for all the help
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