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1947 mack

Posted By Engine 165 4 Months Ago
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Tony Bullard
Posted 4 Months Ago
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I defiantly agree with you about the digital meters. If you have weak connections the voltage may get through but the connection may not pass enough current to to anything. 
Attached is an early Mack 12 volt schematic. Notice how the "Tilt-Ray Switch" is between the "Light Switch" and the Headlamp.


Tony
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Mack '50s Wiring.pdf (9 views, 2.00 MB)
Geoff Weeks
Posted 4 Months Ago
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If you are not getting a full 6 volt at the headlight switch, start by finding out why, nothing matters after that, until you get that fixed. The dimmer comes after the headlight switch.
 For old automotive work I prefer a test light or at least an analog meter. Digital meters can throw you way off as they don't place a load on the circuit being tested and give all kinds of misleading readings.  
Engine 165
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We have 3 volts at the headlight switch but nothing after that I was thinking maybe dimmer switch or something along those lines . Mack sent me a schematic for a non firetruck model but doesnt look the same at all . Like I said after 4 months of playing around with it I am at the end of my rope . So I was wondering if any one had some info on shops or anything like that .
cat herder
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headlight problems on old trucks & cars start with your dimmer switch contacts get  dirty some you can cycle it several times and they might work if not light switch can act the same way. check to see if you have power coming out of either switch then on to bulbs and grounds at bulbs process of elimination. same thing with heater motor , did you check for the mouse condo in the heater box keeping the blades from turning , good luck with your truck!
Geoff Weeks
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I agree, and never have bought or even been around one of those "kits".  But there are those that are intimidated by anything electrical. 
 One big problem is after 60+ years, there are very few molested wiring harnesses to work from.
 Fortunately, one of my K's was virtually un touched for 60 years. The wiring is in tough shape but it is all original.  
Aaron
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Those kits might be aright for a modified hotrod but trying to use one for a stock older vehicle I don't think so, I threw away a hotrod kit on the 37 White some bozo put in and hand wired it as per the book, another idiot had used something on a 47 Cadallic I'm suprised it lasted as long as it did, it got thrown away and wired as per the book.  There are some aftermarket companys that make wiring harness that are orginal, Sac Vintage Ford makes theirs in their shop that worked out really nice.
If this is the only problem to get the lights and heater working and doesn't need a rewire, you'll need to start at the switch for each the headlites and heater, many of these older units had a lot of hot wires coming off of the headlight switch as it would have a single breaker on it, so small stuff like heater,signals,dome light and such would take power from it, but in the case of a fire truck they may have put a breaker panel under the dash for most power what has Mack sent you.


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Geoff Weeks
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Aaron (3/9/2019)
Geoff, do you know of a shop that can repair or rebuild that style of wireing, because some of the things I work on out here morons put small wire hot rod kits in or add fuse panels with drywall screws to firewalls,Its a wonder some of these rigs haven't burnt up. 

I've heard but not looked into it that Ron Francis makes a 6 volt semi universal "kit". Other than that I think it  buy the wire and build it yourself. I don't know of a shop that specialize in building them.
 A few general thoughts for someone considering building their own:
 I have dreams of one day having the time to build a harness for my K IHC's, lacing the harness like aircraft wiring is done. That is very labor intensive, and better not change your mind about what goes where and how many wires you need. I do think it looks good if done well, however.
If I were ever building a harness, regardless of vintage or voltage, I would use a gauge of wire suitable for 6 volts, as it would be fine for any voltage higher, if someone later wanted to "convert" to 12 or higher.
Wiring on old vehicles is simple there isn't too much going on, so lay it out and add wires if you think you may ever are going to add fog lights, or turn signals, and if possible pull the old harness intact to use as a guide.
 Zip ties are quick and easy but don't pass through any loom, They also tend to cut skin when the ends are cut off. I hate them!
 One thing  to remember, never skimp on grounds, they are just as important as the hot wires.  
Tony Bullard
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I agree with Geoff. There is nothing specific about voltage, polarity or truck when it comes to vintage lights and heater motors. The current has to make a loop from the battery through the switch and motor back to the battery. You should be able to trace the voltage with a volt meter through the circuit and find the interruption. There may also be a fuse in the loop.



Tony
Wolfcreek_Steve
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I doubt there is any "complicated" wiring on your truck, old stuff was pretty straight forward.
I have a little book that shows how to do that simple older wiring in terms anyone should be able to understand.
https://www.ebay.com/i/132048646626?chn=ps


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Aaron
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Geoff, do you know of a shop that can repair or rebuild that style of wireing, because some of the things I work on out here morons put small wire hot rod kits in or add fuse panels with drywall screws to firewalls,Its a wonder some of these rigs haven't burnt up. 


Driving the greenies nuts
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