No start with key

[EAG]

Hello,

1951 DeSoto Custom 6 volt positive ground

No start with key. I only get a click. 
I can jump the start with a screwdriver and she starts right up and runs, but not with key. 
And, can only shut it off by disconnecting coil wire. 
I have 6 volts at the ignition switch but on 5 at the solenoid. 
Ignition wire runs to ?horn/ignition relay on firewall. 
Can I bypass that relay and connect directly to solenoid?

Or are there other options or fixes?

[Plymouthy Adams]

first get your schematic for the year and model, your test meter and troubleshoot the problem......with wiring askew it would be impossible for anyone here to state your problem with certainty.   Can you by-pass points of contact, make other changes...of course you can, but unless you annotate these running changes on a drawing for prosperity, you should not.   

[Dan Hiebert]

That sounds like the switch, to me.  A quick check could be to either use a jumper between the appropriate contacts on the back of the switch to see if it cranks the starter, or to remove the appropriate wires from the switch and touch them together to see if it cranks the starter.  If you don't want to do that, you can remove the starter switch and bench test it, but as Plymouthy notes, it is better to troubleshoot the problem than to jury-rig something.  I would isolate where the problem is and fix it.

[Mr.P-15]

Hi EAG:

 

Yes, you can bypass and jumper your way out of almost anything, BUT: let's do a little logic here.....Does the car still have its original 1951 wiring harness? If so, take a good look. Is it stiff and brittle? Can you see any bare wires? Will pieces of insulation flake off with just a little flexing? Do the headlights go dim when the engine goes from road speed to normal idle? Again, is that wiring really 73 years old?

If the harness has been replaced, was it done right? (i.e. with the appropriate gauge of wire) or a slop job by someone who didn't know what they were doing?

Remember the name of the game with 6 volt systems is current, and the more current you are trying to draw, the more deleterious the effect of a given amount of resistance will be.

Worn, frayed and oxidised wiring will have more resistance than wiring in good condition. And it matters: for example, if you draw 12 watts from a 24 volt system, you're pulling a half amp. (24x.5=12). It will be one amp in a 12 volt system (12x1=12) and yes, you can see where this is going, 2 amps in a 6 volt system (6x2=12). Lots of folks will switch out their 6 volt systems for 12 volt because they use wire of a gauge specified for 12 volt systems, because that's what you'll find at the auto parts store. Things will of course, work poorly. Six volts will work just fine when done right. Clean. tight connexions are a MUST. NEVER use those auto parts store battery cables! Triple ought is the way to go!

So, my advice to you would be yes, check the ignition switch, but don't eff around, rip that harness out and replace it. For functionality, peace of mind and safety.

These harnesses are quite simple, I've made quite a few, and with modern insulation you can go up in gauge (down in number) with the same thickness, giving you even better current handling. Supplies are available from Rhode Island Wiring and YnZ's Yesterday's Parts. They will also make the harness for you, even going up in gauge and with original style colour coded cloth coverings if you should so wish. Expect to shell out some buckaroos if they make it for you, though.

I bought my first harness some 30 years ago, but after that I made my own. The process is quite easy, actually: you stretch out the original harness on a board 3 or 4 meters long and duplicate the lines one by one, keeping track of your colour codes, of course. You will want a volt-ohm meter at your side. You can also use the opportunity to add wires that might not have been there originally, such as for turn signals and back-up lights that you will want to add in the future.

 

Hope this helps.