74 challenger doesn't crank.

[yacko]

Hey all,

Just recently purchased a 74 Challenger and was in starting no problem for one week but then stopped cranking.  I replaced the battery and the problem persisted.  I looked at the wiring diagram on http://www.mymopar.com/downloads/1974/74ChallengerA.JPG and figured the problems could be the starter relay or neutral safety switch. 

After some diagnosing, I was checking grounds and somehow the car was cranking and started.  I hooked up a light tester to the positive terminal of the battery and the negative end of the tester to pin G on the starter relay.  Once this happened, the car started to crank.

Now my question is, could the starter relay be faulty, or even the safety interlock switch?  Im trying to figure out how the relay works in relation to my iginition.  From the figure above, Pin G and S are grounded (via ohmeter).  Also, does the nuetral safety switch switch the ground to +12 when the ignition key is turned?

Any tips are appreciated..

Thanks

[GoodysGotaCuda]

Welcome to the forum.

G - goes to the neutral safety switch. The neutral safety switch provides the ground circuit for the coil within the starter relay when in neutral or park.

I - is provided 12v when the ignition switch is turned to "crank". If the ground is provided by the NSS and power is applied by the ignition switch, an audible "click" should be heard from the relay.

S - goes from the starter relay to the starter solenoid. Once the solenoid is energize it actuates the armature on the starter. Once engaged, the starter receives direct power from the battery cable itself.

Now when you stated you used the test light on the G terminal;

Did touching the G terminal with the other end on battery cause it to crank?

Or did you leave the test light hooked to battery +, terminal G, then hit the key (what should have happened if the NSS is weak/inconsistent)

The quickest/easiest ways to diagnose a "no-crank" is to do the following;

If at first the car will not crank in Park, move the shifter to Neutral and try it. It's not uncommon that this works with an intermittent NSS.

If that does not work, I would bypass the NSS completely;

To bypass the NSS, attach an alligator ended wire from Terminal G to a known good ground. By doing this, you completely bypass the NSS. If the engine cranks over after jumping the ground, your problem lies within the NSS/circuit.

...If that does not work;

Using a voltmeter or test light, check for 12v on the I circuit while the key is in the crank position. "I" should have 12v applied to it. If it does, check the starter solenoid terminal "S" for the same 12v. If 12v is on I but not on S, the problem is internal within the starter relay.

If I does NOT have power when the key is in "crank", your problem lies within the bulkhead connections, or the ignition switch itself.

...If that does not work;

Some may do this before anything else. While someone is holding the key in the crank position, using a long extension and a hammer, hit the side of the starter. Be careful not to short the extension to a positive cable on the starter. If that works, your problem lies within the starter itself.

[HP2]

As a '74, my money is on the safety interlock switch. These were wired in with sensors in the seats and the seatbelt systems and were very crude. Like most electrical systems, they have not aged well and being wired through the interior, fared even less so than regular underhood wiring. On '74s, the G terminal on the starter relay runs through the seat belt interlock systems before connecting with the neuteral safety switch in the trans. Like Goody said, running the G straight to ground should allow it to turn over and start.

 

[Jamiez]

The seat belt interlock can be bypassed with a pencil.  However if you just disconnect the 2 wires that go to the bottom of each seat (which is the weight sensor) the car will start without the belt fastened.  If the car is not cranking due to the seat belt, the buzzer should sound and the fasten seat belt light should be lit.