The Stovebolt Site Forums The Shop Area The Electrical Bay Wiring on a 248

Ive got a 1947 GMC 300 with the 248 in it.
I have replaced the coil, condenser, points, rotor, cap and plugs and wires in preparation to try and get spark. The truck has been sitting for over 50 years so i knew i was going to need to replace everything anyway. I "hot wired" the ignition to the coil so i could control it from under the hood. I dont think i have everything hooked up right because im still not getting spark. it could be that the stock wiring harness has a short or break in it somehwere. I can trace all that if i need to.
I just wanted to know what HAS to be connected (ignition wise) in order for me to get spark. Can i bypass the ammeter and Generator leads that go to the voltage regulator? Im pretty sure all I have to do is connect the ignition wire to the coil right? it been a while since I have messed with an older system.

Thanks in advance!

Well I'll go ahead and assume you have a foot starter even though many people don't tell us if they have something different than stock. I am speaking of a Chevy system in 1947. GMC manuals are hard to find. Again assume to be the same. (except for positive ground systems). If same as Chevy otherwise, you will have a reversing switch mounted on the starter. This is before ballast resistors were used. It "saves" the points. If you have that, disconnect for this start up.
Here is what you need for start up. Do not connect anything else. Disconnect everything. You are not using the ignition switch for this. You will not have a charging system or any gauges. You ARE NOT using ANY of the wiring harness per my list.

I DO NOT KNOW IF YOU HAVE A POSITIVE GROUND SYSTEM. GMC USED POSITIVE GROUND UP TO ABOUT 1956. The following hook up should be OK anyway.
If you decide to leave it Positive ground, DO NOT use this info....or reverse the info.

1. Positive battery cable to starter switch big lug. The starter switch is mounted on top of starter.
2. Negative battery cable to starter mounting bolt or a motor bolt.
3. A new positive wire from battery to coil positive. Use this, as you said to shut motor off.
4. I have to stop here and wait for someone else because the original distributor has two hook up spots for this idiotic reversing switch and I don't know which receives the coil negative/how to bypass the rev switch. Probably either distributor terminal can receive neg coil wire.

If your GMC has been updated in these areas, now is the time to explain so that Jerry and others can give you the correct info for a test start.

All of your profile and user name says 1948. You post says 1947...which is it? BIG DIFFERENCE for this discussion for Chevy. This was a transition year 47 to 48. No more reversing switch, electric solenoid option, etc. Both years use the externally resisted coil.
Don't now what Chevy did after reversing switch and until side terminal/ballast resistor? 55.1

Well first off, thank you for the information so far! I am so grateful to have a site like this, its helped me a ton already to try and figure stuff out for this truck.
I changed my signature, when i first got the truck and did a little research i thought it was a 48, but ive dived into it a little more and i am pretty sure its a 47.

So heres the response to everything,
Yes the truck has a foot starter
im not sure if there is a reversing switch on the starter, i took it apart to clean up the contact points and didnt see anything i didnt recognize. What should i look for?
Ill have to look but i think the distributor only has one hookup point, it has the points and condenser hooked up to the inside of the cap and obviously the coil hookup on the outside. its on the lower left side of the distributor.
It all looks like a normal system to me, however im not familiar with the difference in positive ground as opposed to negative ground. Could i get some clarification on the differences for that?
The only other question i have is that there is a knob that turns underneath the distibutor hookup, I know Ive been told what this does but Ive completely forgotten. What it its purpose?
Thanks for your help in advance!

Logan,

Is there a oval metal ID tag on the generator and/or starter?
If yes, what are the codes?

If you have a GMC with the original wiring/electrical system, it would be a positive ground system. The major difference is that the negative lead would go to the starter and then to the ammeter/dash-gauge. The positive lead from the battery would go to the frame.

Did your truck have a battery in it when you got it?
If yes:
- was it 12v or 6v battery
- how was it "cabled" (where did pos/neg cables/strap from the battery attach)?

The round knob is a octane adjuster. Just set it at zero or leave it alone. It won't affect startup.

One thing you need to do is see if any valves are stuck, tap each valve gently with a rubber hammer or end of 2 by 4 to make sure it is not stuck, oil stem first, if stuck, gently work it until it moves, if not, a pushrod may be bent-not good.

Since you seem to be turning it over, still need to make sure all valves are working properly. So do above procedure to each valve.

Ed