Where to use relays?

[ChargerST]

Which circuits should better be run through a relay in your opinion?
To start:

1.) headlights - low and high beams (important with H4)
2.) electric fuel pump (important)
3.) electric fans (important)
4.) taillights (not so important)

[Chryco Psycho]

the first 3 for sure , the taillights are very low current & still have to go through the turn signal switch or you will need 4 realys after the TS switch

[ChargerST]

by taillights I was refering to the brake lights: 4x 21W = 84W/12V = 7A. Not too much actually..if I upgrade to 6 brake lights it's 10,5A.

What's the current draw on items like blower motor, headlight motor, ignition etc.?

[John_Kunkel]

The main reason for using relays is to reduce the load going through the main switch like the headlight and ignition switches.

[Chryco Psycho]

your brake lights still go through the turn signal switch , there are interupted to signal
the draw on the other items you mentioned is minor 

[68neverlate]

The main reason for using relays is to reduce the load going through the main switch like the headlight and ignition switches.

John... how would you use relays to reduce the current going through the ignition switch?  I was planning on proceeding with your suggested mods for the headlight relays, but I'm also interested in how relays could take load away from the ignition switch...        

[Rolling_Thunder]

Well -  the starter relay lessens the load on the ign switch by not making the 12v go through the switch to the starter solenoid wire.  

If you wanted to be all stealth about it - you could wire a separate IGN1, IGN2, and other accessory relay.    this would take almost all the load off the ign switch - which has 12V passing through it constantly when the car is running, in the ACC position, or starting ---  

[John_Kunkel]

The Mopar starter relay is one application where the current load isn't the consideration, the relay merely allows the use of the NSS.

The latching coil inside the relay draws very little current so a lot of relays can be run through the ignition switch without overloading it. In the average sixties/seventies car the headlights and cooling fans are the only place I use extra relays. Most fuel pumps don't draw that much current but many recommend a relay grounded through an oil pressure switch as a safety measure...if the engine quits the pump doesn't continue running.

[68neverlate]

The Mopar starter relay is one application where the current load isn't the consideration, the relay merely allows the use of the NSS.

The latching coil inside the relay draws very little current so a lot of relays can be run through the ignition switch without overloading it. In the average sixties/seventies car the headlights and cooling fans are the only place I use extra relays. Most fuel pumps don't draw that much current but many recommend a relay grounded through an oil pressure switch as a safety measure...if the engine quits the pump doesn't continue running.

Thanks John... appreciate you chiming in.  Was interested what you had to say about the ignition, cuz I really couldn't think of anything other than the starter (which is already on a relay) that was a current load issue. 

Cheers,   

[flyinlow]

Maybe the heater blower? GM used a high blower relay for the high speed on AC equipted cars. Never checked the draw , 10-15 amps running without a resistor?   

[68neverlate]

Hmmm... wouldn't have thought of that one.  I do have factory A/C too.  I'll put that away in the treasure chest for when I complete the relay mods... appreciate your input flyinlow.   

[Dino]

When you do the headlight relay upgrade, does it also affect the instrument panel?  I'd like it to be a bit brighter and more even, the bottom of the clock for example is not very well lit.  At idle the whole thing dims.  I haven't paid attention to it but I can imagine the gear selector light on the console would dim as well.

[Chryco Psycho]

no , it has no effect on the dash lights .

[ChargerST]

When you do the headlight relay upgrade, does it also affect the instrument panel?  I'd like it to be a bit brighter and more even, the bottom of the clock for example is not very well lit.  At idle the whole thing dims.  I haven't paid attention to it but I can imagine the gear selector light on the console would dim as well.

The reason for the dimming at idle is the low output of the factory alternator. Upgrade the alt and the dimming should go away.

[68neverlate]

Make sure if you're upgrading to a higher output alternator that you also upgrade your wiring to accommodate it.  The factory wiring was only intended to handle the factory alternator outputs (max 46 amps).  If you don't upgrade wiring, you risk toasting wires, melting bulkhead connectors, melting ammeters and, worst case scenario, providing your car as fuel for a neighbourhood bonfire.   

An alternator upgrade is what prompted the wiring upgrades I'm doing right now... 

[Dino]

Good info, thanks!

By upgrade wiring you mean the whole thing?  I'm not sure I want to do a job that big and expensive....

Thanks for the heads up though, I would've simply swapped the alternator and called it a day.

[Budnicks]

In my opinion "take it or leave it", as long as it's not a 100pt concourse restoration... Really for any lighting system {especially HID or Quarts head lights, aux/flood lights or fog lights}, any large electronic systems {stereos, amps, alarms, navigation etc.}, electric pumps {fuel or water etc.} or electric motors {cooling fans, wipers, heaters, blowers, etc.}, It's a good Idea to use properly sized & fused relays, they help with voltage spikes & have a constant power source so there is also less amperage draw, on the whole electrical & charging system...  Quality properly sized grounds, engine to body, body to chassis, alternator housing to body...  Also installing a 10ga. wire from the main post at your alternator to the large post on the starter relay on the firewall, will also help shorten the path to your charging system less strain on the alternator, regulator, Amp meter & connection thru the main bulkhead & amp meter splices, especially if you have a trunk mounted battery....   

[68neverlate]

Good info, thanks!

By upgrade wiring you mean the whole thing?  I'm not sure I want to do a job that big and expensive....

Thanks for the heads up though, I would've simply swapped the alternator and called it a day.

It's not necessary to replace everything... the wires that you would want to upgrade (I upgraded to 8 GA for an 80 amp alternator) are the wire that runs from the alternator through the firewall to the factory splice, to the ammeter and then the wire running from the other side of the ammeter back out the firewall to the starter relay via the fusible link (fusible link is 14 Ga).  I'd recommend going directly through the firewall via a grommet with these wires rather than use the bulkhead connector.  My other recommendation would be to use a by-pass on the ammeter to take some of the load away from it. 

Specifics of my modification are contained in the thread below if you're interested.  There are a few other threads covering this topic that Nacho-RT74 has posted as well that are really good... you can find them by searching "alternator" on the electrical board...

http://www.dodgecharger.com/forum/index.php/topic,84766.0.html

Cheers,   

[flyinlow]

In my opinion "take it or leave it", as long as it's not a 100pt concourse restoration... Really for any lighting system {especially HID or Quarts head lights, aux/flood lights or fog lights}, any large electronic systems {stereos, amps, alarms, navigation etc.}, electric pumps {fuel or water etc.} or electric motors {cooling fans, wipers, heaters, blowers, etc.}, It's a good Idea to use properly sized & fused relays, they help with voltage spikes & have a constant power source so there is also less amperage draw, on the whole electrical & charging system...  Quality properly sized grounds, engine to body, body to chassis, alternator housing to body...  Also installing a 10ga. wire from the main post at your alternator to the large post on the starter relay on the firewall, will also help shorten the path to your charging system less strain on the alternator, regulator, Amp meter & connection thru the main bulkhead & amp meter splices, especially if you have a trunk mounted battery....   

I'll take it, a lot of good advice.

[Dino]

Thank you gentlemen, you answered a lot of my questions.

I guess that I'm lucky that all my electrical works and behaves as it should, except for the radio cutting out after a minute.....

Seeing some of the issues that members here have I shouldn't complain that my dash lights dim a bit.
Oh I forgot to ask this, when the dome switch does not work and the dash lights seem to be stuick on high, that means the switch itself is dead right?  Found a spare in the console so I wonder if there's an issue there that keeps ruining the switch, maybe I have more gremlins in there than I thought there'd be. 

I'll have to dive in there with some beefed up wires and relays and have some fun!

[68neverlate]

Oh I forgot to ask this, when the dome switch does not work and the dash lights seem to be stuick on high, that means the switch itself is dead right? 

So, when you say the dash lights are stuck on high, do you mean that they are on high even after rotating the rheostat wheel?  I had an issue with the rheostat when I first bought my car... the variable resistor (the coiled wire in the ceramic disk) was heating up causing the adhesive that was holding the wire in the disk to smoulder.  Those switches are not cheap, so I can see someone trying to modify the switch (bypass the resistor) instead of buying a new one which could be why they're stuck on high... 

Which switch was in the console... a rheostat (dash lights) or a headlight switch?               

[Dino]

Oh I forgot to ask this, when the dome switch does not work and the dash lights seem to be stuick on high, that means the switch itself is dead right? 

So, when you say the dash lights are stuck on high, do you mean that they are on high even after rotating the rheostat wheel?  I had an issue with the rheostat when I first bought my car... the variable resistor (the coiled wire in the ceramic disk) was heating up causing the adhesive that was holding the wire in the disk to smoulder.  Those switches are not cheap, so I can see someone trying to modify the switch (bypass the resistor) instead of buying a new one which could be why they're stuck on high... 

Which switch was in the console... a rheostat (dash lights) or a headlight switch?               

Correct, the dash lights are on high all the time, the thumb wheel switch,or rheostat (never heard of that) doesn't do a thing.  The same type of switch was in the console.  Does this mean that was the original switch and the replacement is now fried as well or is the original still in the dash and is the one in the console the actual replacement, I don't know.  Either way, the spare is not new.  I also found two fuel gauges and an ammeter in the console, definitely old used ones.  All gauges work by the way, fuel gauge only shows 3/4 full when it's topped off so the float must be busted but th gauge itself works fine because it goes down fast when I floor it......   

I'm not sure that the actual gauges and switch were ever replaced as there is a lot of small stuff that came with the car that is not off of it.  I have more switches and nuts and bolts that seem to have been acquired at some point at a swap meet or something as they are all spares.  I even have 3 or 4 ballast resistors in the console!

Seems the only things not working are the right turn signal indicator on the dash, ignition switch light and ashtray light, bulbs must be out because everything else works just fine.

I'll take a look at the coil on the spare switch and see if I can find anything strange.

On a side note, I bought the car exactly 4 weeks ago, put about 600 miles on it so far, driven it rain (not a lot and not on purpose) and shine, I never disconnect the battery and it runs like a trooper.  Very happy with how everything works.  I was literally waiting for stuff to break as the previous owner barely drove it, about 5000 miles in almost 20 years.  The only thing that 'broke down' is that the little switch on the A pillar that activates the interior lights when you open the door sticks a bit.  The last week or so when I open the door, the lights don't always go on, as soon as I touch the switch they work.  I need to take it off, clean it up and put it back, I love the lights in that car, especially the console lights. 

For a 40+ year old car, this thing is surprisingly reliable.  Still not used to the amount of gas it consumes even at cruising speeds though.   

[68neverlate]

If you have a bunch of stuff that looks like it was bought at a swap meet, my guess is the switch in the console was bought to replace the one in the dash.  Check the switch in the console using a multimeter (resistance mode) over the appropriate output/input contacts on the switch while turning the rheostat wheel.  You should see the needle vary in resistance.  Check the other input/output contact for the dome light operation... you should have no connectivity at all until the wheel is turned all the way to the end, then you should have full connectivity.  If those two things check out, you probably have a good switch to replace the one in the dash with (although the variable coil wire could still heat up the adhesive and smoulder like mine did)...     

With the switch that's in the dash right now, does the dome light come on when you turn the rheostat wheel all the way to the end (with both doors closed)? 

[Dino]

If you have a bunch of stuff that looks like it was bought at a swap meet, my guess is the switch in the console was bought to replace the one in the dash.  Check the switch in the console using a multimeter (resistance mode) over the appropriate output/input contacts on the switch while turning the rheostat wheel.  You should see the needle vary in resistance.  Check the other input/output contact for the dome light operation... you should have no connectivity at all until the wheel is turned all the way to the end, then you should have full connectivity.  If those two things check out, you probably have a good switch to replace the one in the dash with (although the variable coil wire could still heat up the adhesive and smoulder like mine did)...     

With the switch that's in the dash right now, does the dome light come on when you turn the rheostat wheel all the way to the end (with both doors closed)? 

I'll give that a try, thanks!

No the dome light only works when a door is open.  I'm confused as to how the roller switch works. I thought all it did was alter the intensity of instrument panel and dome light but the dome light would only go on when you open one or both doors...it's supposed to go on when you turn it all the way up as well? 

[68neverlate]

I'm confused as to how the roller switch works. I thought all it did was alter the intensity of instrument panel and dome light but the dome light would only go on when you open one or both doors...it's supposed to go on when you turn it all the way up as well? 

The rheostat serves two purposes... one is to control the intensity of the instrument panel lights and the other is to turn the dome light on while you're in your vehicle with the doors closed.  When you rotate the wheel from its furthest "off" towards the full "on" position, your instrument panel lights should go from off to full intensity.  If you continue to rotate the wheel a little further (right to the end - you should feel a bit of resistance to get it there), the instrument lights should continue to glow at full intensity and your dome light should also come on (with both doors closed).  This is so you don't have to open a door at night to get your dome light to come on when you're already inside the vehicle.

If your dome light does not come on when the wheel is in its full "on" position, I'd be willing to put money down that someone has done some fidgeting with the switch that's currently in the dash...