electrical systems - The 1947 - Present Chevrolet & GMC Truck Message Board Network

tttuba · 11-13-2010, 07:01 PM

OK I am new to this old truck ownership thing so lots of questions. I am told that the 47 gmc had a positive ground system. My truck was converted to 12 volts and appears it is now negative ground. It also appears the way they converted to 12 volt was to put voltage drop blocks on the firewall. I have a couple questions. First does it matter if the system is now negative ground and any issues with that ? Also can I just change everything over to 12 volts such as gauges and headlamps and coil and distributor etc? Do I need a new wire harness to do this or can I use existing harness?

sweet70beast · 11-14-2010, 04:29 PM

As for the Positive to Negative question I'm not sure, but for the wiring harness question I just changed everything over to 12 volt in my 50 Chevy and used the stock harness. This should only be a temporary thing tho according to some people but I have been driving my 50 for 10 years that way but, I usually only put about 3000 miles on my truck a year. I think it would be a good idea to get a newer harness if your going to drive it a lot.

raycow · 11-15-2010, 10:20 AM

Converting from positive to negative ground doesn't cause any problems except that the ammeter will read backwards. The fix for this is to reverse the ammeter connections, which the PO should have done as part of a proper conversion. You will know if he did this just by turning on the lights (engine off) and seeing if the meter reads charge or discharge. If it reads charge you can reverse the leads yourself.

Ray

11-13-2010, 07:01 PM	#1
tttuba Registered User Join Date: Oct 2010 Location: Olympia WA Posts: 180	electrical systems OK I am new to this old truck ownership thing so lots of questions. I am told that the 47 gmc had a positive ground system. My truck was converted to 12 volts and appears it is now negative ground. It also appears the way they converted to 12 volt was to put voltage drop blocks on the firewall. I have a couple questions. First does it matter if the system is now negative ground and any issues with that ? Also can I just change everything over to 12 volts such as gauges and headlamps and coil and distributor etc? Do I need a new wire harness to do this or can I use existing harness?

11-14-2010, 04:29 PM	#2
sweet70beast Registered User Join Date: Sep 2006 Location: Shelley Idaho Posts: 876	Re: electrical systems As for the Positive to Negative question I'm not sure, but for the wiring harness question I just changed everything over to 12 volt in my 50 Chevy and used the stock harness. This should only be a temporary thing tho according to some people but I have been driving my 50 for 10 years that way but, I usually only put about 3000 miles on my truck a year. I think it would be a good idea to get a newer harness if your going to drive it a lot. __________________ 1970 Nova 327/T5 (my 1st car) 1971 K-20 350/350/205 (winter DD) 1953 GMC Suburban 1968 Chevy Bel Air 1976 Chev C-10 1972 Skylark (suncoupe) 1 of 3943 made

11-15-2010, 10:20 AM	#3
raycow Registered User Join Date: Mar 2003 Location: San Francisco, CA USA Posts: 2,454	Re: electrical systems Converting from positive to negative ground doesn't cause any problems except that the ammeter will read backwards. The fix for this is to reverse the ammeter connections, which the PO should have done as part of a proper conversion. You will know if he did this just by turning on the lights (engine off) and seeing if the meter reads charge or discharge. If it reads charge you can reverse the leads yourself. Ray __________________ Live more responsibly. Eat lower on the food chain. Eat vegetarians. Last edited by raycow; 11-15-2010 at 10:22 AM.



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