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POSITIVE GROUND?

Started by ski, August 25, 2007, 05:56:17 PM

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ski

I briefly tied to start the 29 plymouth I recently purchased and quickly realized there was a ton of water in the fuel system.  I pilled the tank, the carb, the retrofitted elec. fuel pump and cleaned them all.  I pulled the battery out at the same time to charge it.  I've since realized that this is probably a positive ground system.  I didn't take notice when I pulled the battery but looking at the terminals (one being bigger than the other) it seems like the battery had been installed with negative to ground.  The car had cranked and I was getting spark to the points and the head lights worked. Would it still do that if the battery had been hooked up wrong?  I don't want to fry anthing when I hook the battery back up.  Any advice?

Thanks,
Sean

chetbrz

Quote from: ski on August 25, 2007, 05:56:17 PM
The car had cranked and I was getting spark to the points and the head lights worked. Would it still do that if the battery had been hooked up wrong?  I don't want to fry anthing when I hook the battery back up.  Any advice?

Thanks,
Sean

Reversing the polarity of the 29 would still allow the lights, horn and starter to crank.  You may have a problem with the distributor in that it is the only device in the car that would be polarity sensitive.

You are correct in that this car was originally Positive Ground.  It could be wired as negative ground if the distributor coil was changed or if the coil wiring was reversed.  My car does not have an original distributor so I can't give you any advice as to what to look for.

See original wiring diagram:



Chet...
http://www.1948Plymouth.info           Web Master - Forum Administrator - AACA member

ski

My coil is mounted directly behind the ignition key on the other side of the dash. (which was a new one to me)  I'll have to get under there and check it out.  Thanks for the diagram.  I'm hoping the coil is labled in some way so I can tell if the wires were changed.  If not hopefully the colors can still be distinguished.  Anyone else running an electric fuel pump?  I mounted mine back by the tank without drilling any new holes in anything and mounted the regulator on a panel I made that goes where the vacume canister was. I'm keeping everything so I can put it back to original once I see what I have. The gas tank doesn't have a vent which won't be a problem with the ill fitting cap and fuel gage but once I get them tight is some kind of vent needed?  Thanks again.

Sean   

chetbrz

If you had water in your gas you may most likely have rust in your tank.  I don't know how long the water has been in there but if it has been sitting for awhile you may have clean the tank and coat it with a gas tank paint. 

Here is a link to what I did with my 48 P15 tank.  Some guys use chain instead of gravel.

http://www.chetscoins.com/1948p15/20045/09182005.htm

As far as a cap you need to use a vented cap or in my case just a loose fitting cap.  If not you will build pressure in the tank and on a hot day the pressure will force two much gas to the carburetor.  Also you can collapse the tank if you have a good electric fuel pump.  I also use an electric fuel pump.  It is rated at a maximum pressure of 2 psi.  I had a 4-5 psi pump and it forced two much gas into the carburetor and caused it to pour out the front. 

I am glad the wiring diagram helped you.

Chet...
http://www.1948Plymouth.info           Web Master - Forum Administrator - AACA member

ski

Thre tank is good inside.  It had recently been cleaned and sealed.  I cleaned out the inside good and rinsed with gas.  The outside was coated with a rubberized paint but poor prep work led to a lot of rust bubble through.  I took them all down to bare metal and painted with rustoleum.  I may spray undercoating over this. 

I removed the coil to have a look and to replace the wire going to the amp meter.  The coil has no pos or neg markings.  The terminal on the R/H or passenger side of the coil as it's mounted in the car goes to the distributor.  Can anyone confirm that this is the proper coil wiring for a positive ground?

Thanks,
Sean

Old Plymouths

Hi
All the old Plymouths were positive ground. The coil has only one wire on it because it could not be changed to negative ground. Later universal coils had 2 wires on them,+ and -, and could be used on either ground polarity. If you dont' hook up the battery as + ground the spark strength will be reduced and hard starting and poor gas milage will result. The starter motor and lights  don't care but the ammeter will read backwards.
  The generator is another matter. It has to be 'repolarized' BEFORE starting the engine in the other polarity or else the generator will self destruct. Usually the 'cutout', the little black box item on the generator housing, burns up first.
  Since this is an old post,did you ever get everything sorted out?   

ski

Yes I did get it sorted out.  I hooked it up positive ground and it started and ran fine.  The ammeter was working properly.  I think the prior owner had hooked it up Negative ground when he bought a new battery to try and get it running but he never did so I'm hoping the generator is okay.