I am working on a '70 Duster that seems to be winning, it's been sitting for ~15 years for reasons unknown.

While trying to get it running I noticed that I cannot get the ignition switch to trigger the starter relay. If I jump it, it works just fine. I turned the key "on" and jump the relay, engine runs pretty decently.

As I've traced the ignition switch issue, I have the following notes:

• Healthy Charged Battery
• ~7.0v to the yellow starter relay wire when key is in "Start" [should be 12v]
• Pulled the ign switch down, I get 12v at the red wire, but it goes down to 7v when the key is turned on. Seems like somewhere down the line a component cannot manage any current.
• The 7v is also effecting the fuse box as the keyed fuses also are at 7v.
• Pulled apart and cleaned the bulkhead connectors, nothing seemed corroded enough to mention
• Fusible link at the bulkhead has continuity, but I haven't been able to run a voltage drop on it yet. I assume a fusible link will either work...or not. Having low voltage doesn't seem like a fusible link issue to me.

We are just trying to get the car to move around the place under it's own power for now. I am not looking to do a full ammeter bypass and such, if I do not have to [for now].

I am nearly out of ideas other than just trying the bulkhead/ammeter bypass and hoping for the best...any other ideas to try?

we'll assume the batt is a good one. Cranking voltage may be in the 8's or 9's EVERYWHERE just while it is trying to start. You cant do alot of voltage checks while cranking as it will run down pretty fast. I would continue to clean ALL terminals/connections including ground paths. My gut is telling me that something is draining too much current such as the starter (the slower a starter turns the more current it draws/opposite of other electric motors) IF the battery is not the problem. What I would do first is make up a long jumper wire with alligator clips & jump from the batt positive post to the ign sw & see if it cranks OK. Holler back when you find out anything

I agree with RR, it sounds like a dirty connection limiting the voltage to and from the ignition switch. Do you have access to a wiring diagram or wiring schematic? If so start by measuring the voltage going to the 12v lead the ignition switch from the main bulkhead connector, if the switch has less than battery voltage with the switch off then look at the 12v connector in the bulkhead with that harness unplugged
As RR said it may be dirty and corroded causing the voltage drop
the other thing may be as you have suggested is the fuseable link connection on the bulkhead connector also
What ever is causing it can be fixed by you

My first guess would be the fusible link wire at the firewall bulkhead connector as already suggested. You could try wiggling the connectors while you have the volt meter hooked up. It might show you where the bad connection is. Also, most of the circuits go through the ammeter on the gauge cluster. I've seen the bolted connections on the ammeter loosen up and go bad too.

Thanks Robert.

The Battery voltage while in "start" remains at 12v, because I can't trigger the starter relay with only 7v going to it. So the starter itself is not consuming any current.

I'll try the long jumper and see how it goes. The ammeter dips about 1/8" when I turn the key on, nothing appears to be coming on when I turn the key on..perhaps something is there. Car is completely stock with no wiring hacks or add-ons.

I do have a wiring diagram and am going through it the best I can.

The large red wire on the ign switch goes down to 7v when I turn the key on, as does the switched fuses. That red wire goes to the bulkhead, then the fusible link, then to the starter relay.

Is there a direct replacement fusible link out there? Given it goes directly to the bulkhead connector, replacing it is a bit difficult without a new pin.

i would test voltage on that red wire unhooked from the relay.
also run through those other wires that are dropping to 7v, unhook them and retest and see if there is a component that is draining voltage...

it could also be the 12ga [10ga ?] wire going to the starter solenoid from the relay. i ran into that one time, and it drove me nuts trying to find out why the starter wouldn't engage, no matter what i tried !
after i changed the battery cable [this wire is part of the cable going to the starter] with one from the pile of unknown application, it has worked flawlessly since.
as that appeared to be the problem, i inspected that wire very close. it had a crack in the insulation, and under the insulation crack[s], the wire had turned green. i removed the insulation in both directions until i came upon nice copper strands, and it was almost 1 3/4" long. green with white dust similar to battery acid damage/corrosion.
just my experience, but maybe something to look at.

Might check the ammeter connections as all of the current inside the car goes through it

After decades of working on car wiring systems, I've come to the conclusion that the majority of the problems are 1) poor connections, and 2) poor grounds. For your case, you say you have 12v at the ignition feed with the ignition off and 7v with the ignition on. That tells me you have a poor connection prior to the ignition switch. With the ignition on, just start following the wiring connection by connection back to the battery. Somewhere you will get your 12v back and there is your problem. The trick is to systematically start and work through the system in sequence. "Shotgunning" is rarely successful.

Voltage is able to run throught a hair but as soon some load is required, this is not enough and get a voltaje decay.

Time to check bulkhead red and black wires and ammeter studs. The ign switch takes the power from black side of ammeter from a splice into the underdash harness. the splice itself is hard to beat, but after 50 years, the ammeter must be checked.

The studs inside the ammeter are "riveted" ( somehow smashed really ) to the shunt inside the ammeter assembly. With the lack of power coming from stock alt the shunt begings to overheat due the stress added being allways forced to handle loads that could be not necesary to handle for long times if a correct alternator was installed by MaMopar. This heat over the shunt stretchs the shunt making the amm stud to loose from it and missing conection, causing more heat. This makes to rust the stud outside and terminals attached.

and of course the terminals mentioned at bulkhead also begin to heat, melt and rust.

If just a better matched alt was used fom factory!!!!

How many amps is the starter drawing when trying to start?
You say you have to jump it at the starter relay,did you check continuity on the neutral safety switch harness?
Does it start in Neutral?
Did you ground the wire at the starter relay (that goes to the neutral switch) to body and did it start by the key?
If so a ground issue is present or open circuit in the neutral safety switch
hope this helps