I have been helping a good friend with a 49 F1. We have started sand blasting on the cab and have the gauge cluster out and all the wiring under the dash exposed. We looked for the reducers because the truck has been converted from 6v to 12v. There are none. None on the gauges, none on the wiring harness. The gauges are the original 6v. The way I understand this is that the gauges will burn up when the change over is made without reducers. All the gauges work including the fuel gauge. Am I just not understanding how this works or what ? There is nothing on the back of the gauges like what I have seen on the site and nothing on the 12v fuse block. Can anyone tell me what I am missing? Thanks

 

Some gauge sensors aren't simple resistors, they are pulsing bimetallic strips. It is true, they will work on 12v, but their life will be significantly reduced.

The ammeter doesn't care what voltage is; the oil pressure is a resistor and will read wrong; I think the gas gauge is also a resistor. The temp gauge will work pretty well.

 

Thanks Ross, all of the gauges on the truck seemed to work correctly. I followed the wiring tonight efore I left the shop and I couldn't find anythiong different than what the diagrams show. There was one metal strip on the back of the gauge cluster but that was all. The wire from the alt. just ran through the back of the amp gauge. It didn't attach to anything just through the loop on the back of the gauge. Can't find anything on the fuel gauge but it reads correct as far as a I can tell.

 

What you are missing is that there HAS to be some sort of reducer somewhere on a 12 volt system or the gauges would not work correctly they'd fry. There has to be either a small resistor type on the back of each gauge (which you indicated was not there, or there was a sugar cube size reducer the attached to the back of the instrument panel, or you have a Vol-ta-drop type voltage reduced mounted somehwere else on the truck - firewall maybe.

Question is if the truck has been converted to 12 volt (and how do you know it has - 12 volt battery? Does the battery maybe have a stud with a nut coming out of it's top center) How are you distributing power. In that truck the wire from the "BATT" terminal of the Generator used to go directly to the "BATT" terminal of the 30 amp circuit breaker of the two circuit breakers on the back of the instrument panel. Are those breakers still there? And is power still being distributed off them (power to your gauges used to come off the "AUX" post of the 15 amp breaker. If not, then where is it coming from....ie....where do your gauges get power? Trace that input and if the thing actually is 12 volt now, you will find your reducer - somewhere. Gotta be! 12 volts will fry the gauges in about 15 seconds without a step down.

There is one other possibility, the gauges were rebuilt to function with 12 volts. There are companies that do this, but it's expensive. Also, it is very easy to take 56 gauges and put the 48-55 (all of which were 6 volt) faces on them and use the 56 sending units and have them work as well. They were all the same physical configuration. Only th emounting and backing plates were different to suit th eappropriate panel - and even those were interchangeable. I actually put mechanical works inside my stock 51 gauges and replaced the faces. Work great, very accurate, not voltage dependent

 

The 56-on gauges are also 6v gauges; Ford just put a CVR in front of them. They did it that way well into the 60's.

I've read of many guys who own '40's Fords (cars and trucks) who did absolutely nothing and everything worked well enough that they just left them that way.

 

It could be, but everytime I applied 12 volts to the 6 volt gauges, the needle swings up fast, there's a little puff of smoke, the very fine wire windings melt away, and the needle never moves again. Maybe it's just me or the gauges I've tried it with. And I don't remember there being a CVR on my 56 gauge package, but I could be wrong and just not have found it - like is possible here.

LMC sells 53-56 repro 12 volt gauges with no CVR. There are lots of possibilities. But running unadapted 6 volt gauges on a 12 volt system and having them be acurate is not physically possible.

 

Check the battery, an old friend told me that back in the day they would use screws to tap into individual cells of the battery and run 6 volt off a 12 volt battery.

 

Yep, that is that stud I mentioned up in post #4. My boat used to have one of those when it had the Studebaker flat head in it.

 

Ross, I learned somewhere, maybe on this site, that the 56's were changed to 12volt on the guages. Then for some reason in 57 they went back to 6 volt for the guages and started using a instrument cluster resistor up until 72 to cut the voltage to the guages down to 6 volt.

 

That sounds vaguely familiar... that modern stuff just confuses me

 

As cheap as Old Man Ford was, nothing like that would surprise me. They probably found a big box of 6 volt gauges and decided to reface and install them with a CVR to save a few PENNYS!