TheSamba.com :: View topic - Couple electrical questions…rail buggy wiring

Mon Oct 26, 2009 6:24 pm

Just preparing for my winter project…

Blinker relay...which relay do I need if using a single blinker indicator? I’ll be using the indicator in a factory 68/69 speedo. I’ll also be using an additional (single) indicator in my switch box but in either case it’s still a single indicator (circuit) needing to flash when either side is switched on. I learned today the altenator, blinker & oil indicators lights in a factory speedo are powered "hot" by the ingnition though only illuminate when ground is connected. The wiring diagram I have shows the use of a 3-blade relay…they show the 3rd leg wired directly to the speedo indicator. My plan was to run hot wire from ignition to fuse, fuse to relay, relay to on/off/on switch, switch to right/left circuits. Is this third leg connection to the indicators correct…does it supply the connection to ground needed to blink the indicator? Do I need a specific relay or will any 3-blade relay work? I would assume the relay needs grounding? Is this correct?

Altenator Idiot light…Wiring of the altenator idiot light is understood...i.e. I know what the wiring diagram tells me though I don’t exactly know how the wiring loop creates a voltage drop on the light when the altenator charges. However this is not my question. I am again planning to use the indicator in the speedo along with an additional indicator in my switch box. My plan…second light, also powered by ignition, while connected to ground through the same light in the speedo. Will this aditional light in the circuit allow the charging system to function correclty?

Thanks, Toby

Mon Oct 26, 2009 7:04 pm

Technically its not called a relay, its called a flasher...... You have it pretty well figured out.... Most flashers (generic autoparts) have two versions two prong and three prong..... Either will work, it all depends on how the indicator is wired in...

Here is a couple of examples....

On the alternator light, the alternator at rest (not spun up) puts out a ground on D+. This grounds is the component that lights the alt lamp, because it has 12 volts on "other" side of lamp. As alternator spins up and start to produce electricity, the ground at terminal D+ (AL 82) or the voltage change at the B+ lean on regulator (AL78) become a positive voltage. Once you have a positive voltage on each side of lamp there is no current flow, this lack of current flow causes lamp to go dark...

Dale

Dale

Mon Oct 26, 2009 10:43 pm

Thanks Dale. I hadn't even considered placing the indicator light before the switch.

On the altenator...will it make a difference if I use two indicators?

For example I could power the speedo indicator off ignition from fuse...then run D+ to this indicator. In my switch box...I would also power this indicator from ignition then I can pull ground from D+ by either running back to altenator or forward to the bulb on the speedo.

Would this work?

Tue Oct 27, 2009 5:52 am

Toby from MO wrote: Thanks Dale. I hadn't even considered placing the indicator light before the switch.

On the altenator...will it make a difference if I use two indicators?

For example I could power the speedo indicator off ignition from fuse...then run D+ to this indicator. In my switch box...I would also power this indicator from ignition then I can pull ground from D+ by either running back to altenator or forward to the bulb on the speedo.

Would this work?

is this what you were thinking about?

yes, it would work.

Tue Oct 27, 2009 9:44 am

The only problem you may encounter using two indicators for ALT is that it lowers resistance in indicator light circuit and allow voltage/current to bleed through the two lamps and cause a condition called "run-on"... Its a condition where you get a voltage feed back through the lamps that is enough to power coil so engine stays running when you turn key off. BUT it is easily enough fixed, by adding a "run-on" prevention diode...

Dale

Wed Oct 28, 2009 3:17 pm

What are the odds!

I took our sandrail out of storage in preparation for our annual trip to pismo.
My idiot charging light burned out, so I made a simple
jumper wire to bypass it and compete the circuit from alternator and positive.

Sure enough my rail would start and run fine, but would not shut off.
I thought I screwed something major up.

This was last Thursday. I was just going to post a question but you already answered it.

here is my new question.

Is there a better solution for a charging light than an incadescent bulb?
If the bulb burns out would'nt the battery die and leave you stranded? Seems like a bad design.

Is it possible to run a bulb in parallel with a resister?
That way if the bulb goes bad you are still charging the battery?
I'm running about 250 watts of lighting and the battery will quickly run down without the alternator moving electrons.

Wed Oct 28, 2009 7:15 pm

You can run LED pilot lamp instead of incandescent... You can use a 12volt automotive LED pilot lamp with additional diode and a resistor wired across LED... Resistor causes voltage drop across LED and that causes LED to illuminate and added diode is for run-on prevention...

Diode with circle around it with arrows is electrical symbol for a LED... Yes it is polarity sensitive, if its backwards it will not work...

Dale

Fri Oct 30, 2009 10:17 am

that looks exactly what i would like to do. A LED has no filament to break due to vibration. Plus if it does the resistance provides continuity to complete the charging circuit.

thanks a million for the diagram. I'll add to my low cost no cost improvement list of things to do to our sandrail.