6 Volt Positive Ground

[Al Peterson]

I know everyone’s favorite thing to do...6 volt wiring!

 

I have a ‘47 WC with no lights except dash lights.  I have tried several different things to get headlight and tail lights.  No luck.  I jumped the system and hooked them up direct to see if the bulbs were good, they worked.  I am completely frustrated.  The wiring is old and faded, so tracing them is a bit of guess work.  So after work I decided to route all new wires just to get the one tail lamp to work.  I wired it exactly like the schematic indicated(new light switch too).  No lights.  

 

I need help.

[Don Coatney]

Is there a FUSE on the back side of the light switch?

[Al Peterson]

The OE  did have one but I replaced it figuring that was part of my problem.  The new switch has a circuit breaker.  

[Dodgeb4ya]

Does the dimmer switch check out OK?

[Al Peterson]

Dodge4ya,  I replaced it because it was for sure bad.  The original was shorting out on high beam.  

[Al Peterson]

Tonight I only had enough time to put a new ground in from the  positive  cable directly to the cab.  I probably won’t have any time tomorrow but will update my progress.  

 

I already cleaned the positive cable connection from the battery to the manual transmission(OE mount?).

[jeffsunzeri]

11 hours ago, Al Peterson said:

Tonight I only had enough time to put a new ground in from the  positive  cable directly to the cab.  I probably won’t have any time tomorrow but will update my progress.  

 

I already cleaned the positive cable connection from the battery to the manual transmission(OE mount?).

Ground your battery to the engine block. There are a few tapped holes just below the oil galleries for this. Then you should have 2 ground straps - one from engine to the cab and one from engine to the frame.

 

 

[Al Peterson]

1 hour ago, jeffsunzeri said:

Ground your battery to the engine block. There are a few tapped holes just below the oil galleries for this. Then you should have 2 ground straps - one from engine to the cab and one from engine to the frame.

 

 

Are you saying I should have it to the engine instead of the transmission?  That looks like the factory location but I could be wrong.  

[JBNeal]

Factory ground to the transmission is prone to increased impedance as bolt and tapped threads corrode over time, as the voltage path to ground passes thru more mechanical attachments.  My generator / starter guy suggested grounding the battery at a starter mounting bolt, as the starter has the most current draw...this should improve cranking and reduce impedance as the chassis ground is placed closer to the current load.

 

Edited May 24, 2021 by JBNeal
added link

[jeffsunzeri]

2 hours ago, Al Peterson said:

Are you saying I should have it to the engine instead of the transmission?  That looks like the factory location but I could be wrong.  

Yes, ground to the engine. It is preferable NOT to ground under a bolt that is used to hold or assemble a subassembly. The cable/strap acts as a soft washer under the bolt head which is a no-no.

[ggdad1951]

20 hours ago, jeffsunzeri said:

Ground your battery to the engine block. There are a few tapped holes just below the oil galleries for this. Then you should have 2 ground straps - one from engine to the cab and one from engine to the frame.

 

 

there should be no need for ground straps if you have properly cleaned connection points where you run your grounds.  Ground straps are a "cheat".

[squirebill]

I'm thinking if you have dash lights your grounds are good.  If you by-passed the light switch and went with a hot wire directly to the head light hot leads and the bulb lit, the ground for the head light is good.  This gets me back to the wiring diagram.  I compared your diagram for the 47 WC against my diagram for a 49 B1B.  Looks like they both have the 6 terminal light switch. My headlight wire comes off the terminal of your wire 28 at your headlight switch.  My headlight wire goes from the headlight switch to the input terminal of my dimmer switch then out of the dimmer switch to the HI and LO of my headlights.  Your wire 28 comes off the headlight switch, goes to item "L" (a connector?) and then becomes wire 13, goes to item "E" (a terminal block?).  Off of item "E", wire 12 feeds a single bulb "V".  Your wiring diagram is cut off and doesn't show me where the other two wires from item E are going. So the question becomes: do either of these two wires come back and feed the input of the dimmer switch, item V.  You have to have a Hot wire coming off your headlight switch and feeding the input of the dimmer.

[Al Peterson]

update:  The long and short of it is a ground issue, which I figured but I did assume the painted taillight mounts were removed and cleaned when painted.  They were not.  So I cleaned the mating surfaces and both taillights and brake lights worked great.  The headlamps didn't work either, I did have to replace the dimmer switch as well.  Once I took the lamps out, the mystery was solved.  First, the bottom of the lamp assembly was fiberglass reinforced and thusly creating a barrier to it being grounded.  Secondly, the headlamp harnesses were in terrible shape.  

 

A big thanks to everyone for your suggestions and help!

 

[Al Peterson]

27 minutes ago, squirebill said:

I'm thinking if you have dash lights your grounds are good.  If you by-passed the light switch and went with a hot wire directly to the head light hot leads and the bulb lit, the ground for the head light is good.  This gets me back to the wiring diagram.  I compared your diagram for the 47 WC against my diagram for a 49 B1B.  Looks like they both have the 6 terminal light switch. My headlight wire comes off the terminal of your wire 28 at your headlight switch.  My headlight wire goes from the headlight switch to the input terminal of my dimmer switch then out of the dimmer switch to the HI and LO of my headlights.  Your wire 28 comes off the headlight switch, goes to item "L" (a connector?) and then becomes wire 13, goes to item "E" (a terminal block?).  Off of item "E", wire 12 feeds a single bulb "V".  Your wiring diagram is cut off and doesn't show me where the other two wires from item E are going. So the question becomes: do either of these two wires come back and feed the input of the dimmer switch, item V.  You have to have a Hot wire coming off your headlight switch and feeding the input of the dimmer.

 

 

I inadvertently cut out the brake light switch in the photo of the schematic.  

[JBNeal]

additional information - Ground Strap Information

Edited October 17, 2019 by JBNeal
revised link

[lonejacklarry]

I used to fool with British cars years ago.  About 98% of electrical problems could be traced to bad grounds.  Oh, yes, they might look good but corrosion has a way of creeping into the fastener and reducing the effectiveness.

 

Since that learning experience I've come to check the grounds whenever there are problems.  I am rarely disappointed with that philosophy.  The 98% rate stands with old American cars, too.

 

[squirebill]

Once again, grounds and the  heavier gage of wire for a 6 volt DC system comes around to bite somebody.  But for my own education please advise where the two unmarked wires coming off terminal block E finally connect.  Does one of them finally connect to the input of the dimmer switch? Regards. 

[Merle Coggins]

To me it looks like "E" is the dimmer switch. One wire in, two out (leaving page) possibly going to headlights, and 4th going up to high beam indicator "V".

Edited July 26, 2018 by Merle Coggins

[Al Peterson]

1 hour ago, squirebill said:

Once again, grounds and the  heavier gage of wire for a 6 volt DC system comes around to bite somebody.  But for my own education please advise where the two unmarked wires coming off terminal block E finally connect.  Does one of them finally connect to the input of the dimmer switch? Regards. 

 

 

"E" is the dimmer switch and the Brake Switch is missing in the photograph.  

[squirebill]

Hope you don't mind laying a couple more lashes on this dead horse......but could you please advise what are items "Z", "EE" and  "DD" ?  

[Al Peterson]

10 minutes ago, squirebill said:

Hope you don't mind laying a couple more lashes on this dead horse......but could you please advise what are items "Z", "EE" and  "DD" ?  

 

I am more than happy to clarify.  Z is the gas gauge, EE is the fuel sending unit and DD is the tail lamp.  

[Merle Coggins]

Since Al has the book with the "key", he'll have the definitive answer. But I'd venture a guess that "Z" is the fuel gauge, "EE" is the fuel level sensor, and "DD" is the tail/brake light.

 

Edit: Al's reply beat mine. but it was a good educated guess

Edited July 26, 2018 by Merle Coggins

[Al Peterson]

I have an additional question about wiring, I'll be replacing my wiring harness and was wondering about what would be best in regards to adding an additional brake light.  What is the best way to do that?  Should I run a completely separate wire(s) or should I tap off of the existing harness?  If so, should I do it towards the rear and route it along the bed support?  Any ideas or suggestions?  The person that owned the vehicle before me did add the brake light but used a Scotch Lock and I'm not going to use that type of connector, it's asking for trouble down the road.  Thanks in advance.

[Jocko_51_B3B]

Al, you probably have your new harness installed by now, but when I ordered my wiring harness  I told them I wanted brake and running light wiring for both sides. They simply added two additional wires for the passenger side (near the back end of the harness) and wired them in parallel with the driver side wires. Based on the short length of the two added wires, it's pretty clear they intend for them to run along the bed support. Connections to the brake light switch were unchanged.

Edited March 1, 2020 by Jocko_51_B3B

[Al Peterson]

On 2/29/2020 at 6:22 PM, Jocko_51_B3B said:

Al, you probably have your new harness installed by now, but when I ordered my wiring harness  I told them I wanted brake and running light wiring for both sides. They simply added two additional wires for the passenger side (near the back end of the harness) and wired them in parallel with the driver side wires. Based on the short length of the two added wires, it's pretty clear they intend for them to run along the bed support. Connections to the brake light switch were unchanged.

I ended up making my own, or am in the process.  I just finished the lighting harness two days ago, I plan on doing the under dash one tonight.  At this point I don't plan on putting turn signals in but I did run a second taillight.  I'm not opposed to turn signals, just haven 't done any research on keeping it 6V with signals.