Packard Forum Index » Modification Discussion

Hi
Yes my project is still on going!!!!
I would like to know what i need to do to run the gauges on a 12 volt negative ground system?

A possibility might be to use an instrument voltage regulator from a 55-56 and power the gauges from the output of the regulator as is done from 51 on. Downside is the 49 gauges are slightly different than the later gauges and wired directly to 6.3-7v in normal operation. The regulator puts out an average of 5 volts. Since the gauges in the 48-50s use a bimetal type sender with a heater element to control the action of the bimetal strip, the lower voltage may not be enough to power the heater to make the senders and gauges read properly.

I don't know if Runtz reducers are available in Australia but that would probably the simplest and safest to ensure proper operation although not the cheapest since you have 3 gauges needing power and each needs an adapter.fifthaveinternetgarage.com/electrical_parts.php
Here is one of many sites selling them. Scroll down the page to view the item and instructions.

Thanks for that I will see if they are available over here im sure there will be an equivalent available.
Do i need to change anything in tegards to going from a positive ground to negative ground?
And will my amp meter work if i just change the polarity?

Thanks just had a look at that parts shop also found that i can use a 6 volt inline diode which i have seen at the electronics shop Jaycar just need to reserch the correct specifications.

Your amp meter will work fine by swapping the wires.

Since you are going to 12v there are some other things to be concerned with The starter solenoid needs to change and it would be a good idea to have the starter motor windings changed to 12v. There was a rash of posters experiencing expensive starter failures last year due to the nose castings being cracked or completely broken off. The common thread was all had been running the stock 6v starter on 12v until the increased torque and pinion slamming into the end stop from the vigorous 12v action finally broke the cast iron. Am assuming you will get a new coil so for best efficiency the coil needs to have the wires reversed so the negative terminal goes to the dist. If you are keeping the old you will need to add a ballast resistor.

If you have an OD that is another item. You can get 12v solenoids and relays for the R12 so not as big a deal as the R9 but a cheaper option might be to get a 6v power supply to run the OD, radio (if you plan on keeping the stock radio), and the heater motor(s).ebay.com/itm/Voltage-Reducer-Regulator-1 ... 31850236348?hash=item1eb2e2f1bc:g:i~cAAOSwDNdVx6qR&vxp=mtr

If you wanted to run more wires you could also power the gauges from the same power supply instead of using the Runtz or diode but it gets a bit involved the more you add to a dual voltage system.

Thanks.
I think i might use the diodes for the gauges this will make it easier as I can just run them from the fuse box that i have installed on the inside of the firewall as i am rewiring the whole car from scratch!!
I have installed a new 12 volt coil and changed the wires around.
I will make some enquiries at my local auto elect and see if he can convert the starter over.
If i just change the polarity on the gauges will that work?

Gauges are essentially two heater elements so they don't care about polarity -- but they do need the correct voltage so the elements don't burn out.

Thanks that makes its easier to know that the gauges will work.
I dont get much time to work on my car and sort of lost my way with it but have recently gone back to it and need to keep focused on the goal (Driving my uber classic very rare in australia 2 door 1949 Packard)!!!!!
Cant wait to instal my 50th anniversary gold gauges in with my restored wood grain dash!!!

Good advice from the above posts. One additional comment. You will need a ballast resistor with your new 12-volt system coil if it is the type requiring an external resistor. You can also get a 12-volt system coil with an internal resistor. Either will work, but do not connect an external ballast resistor to a coil with an internal resistor. Also, those ballast resistors get hot and need to be mounted where they do not come into any contact with wires or hoses, and have plenty of room to dissipate the heat.

The ballast resistors are wired so that the resistor is by-passed during the starting of the engine allowing the full 12-volts goes to the coil, and then current is routed through the resistor after the engine has started. This may not be a need for your modification, but it was the conventional practice.

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Thanks for the great advise was some time since i installed the coil have had it running with it on i will double check but im sure its the type that doesn't need a ballast resistor.
Thanks