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Relays and fuses?

Rusty 72

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Hi.

I'm gonna add some relays for the high draw blower, headlights, etc. I still have the stock set-up on my 72 Charger.
I'm using a through the firewall main positive stud for power to the dash harness and I had bypassed the ammeter in the past. I'm using a one wire alt wired directly to that firewall stud. So you have an idea of what I'm doing if that makes sense.

My question is, do I need to add fuses to the relays? And are the cheap (Amazon) fuse panels ok for a fuse block?

Thanks in advance Jeanette

61Rsuf3PO4L._AC_UL200_SR200,200_.jpg
 
Hi.

I'm gonna add some relays for the high draw blower, headlights, etc. I still have the stock set-up on my 72 Charger.
I'm using a through the firewall main positive stud for power to the dash harness and I had bypassed the ammeter in the past. I'm using a one wire alt wired directly to that firewall stud. So you have an idea of what I'm doing if that makes sense.

My question is, do I need to add fuses to the relays? And are the cheap (Amazon) fuse panels ok for a fuse block?

Thanks in advance Jeanette

View attachment 968326
Yes, any load should be fused. The attached fuse block picture looks OK.
Mike
 
To the OP,

The headlight and the wiper motor power source should never have an in line fuse, period! Every car made by Chrysler had a hidden breaker, (20 amp for the headlights) and (5 amp for the wiper motor) in every switch as a safety precaution. How many times will a blown fuse "reset" while driving at night? If you are increasing the amperage load for the headlights, do the math and install a circuit breaker only with at least double the load capacity for the amperage draw. A four headlight stock from the factory draw was just under 3 amps per bulb with the breaker just under double the rating.

Jim
 
Where are these hidden breakers you speak of?
 
Where are these hidden breakers you speak of?
The OEM headlamp switch has a circuit breaker built into the case, but if you are adding high draw head lamps I assume you are going to actuate them with relays. The lamp switch breaker will protect the low voltage side of the relay circuitry but you still need protection for the high draw circuitry, breaker or fuse-your choice. On my car I used 2 relays, one each for high and low beams and placed them in a small box behind the battery for some concealment.
Mike
 
These guys got it you must cover both sides. High and the low I would work with resettable breakers. Don't like driving in the dark.
 
The lamp switch breaker will protect the low voltage side of the relay circuitry but you still need protection for the high draw circuitry, breaker or fuse-your choice.
Mike
Wow!!! There is NO/ZERO choice on using a fuse or circuit breaker on the output side, even if you using relays on the load side. How many times will a fuse reset, once blown?

Where are these hidden breakers you speak of?
Here are some pictures showing these original factory 2947305 headlight switch with a 20 amp internal circuit breaker and a 2770380 variable speed wiper switch with a 5 amp internal circuit breaker.

IMG_1285.jpg
IMG_1286.jpg
IMG_1287.jpg
IMG_1288.jpg


Jim
 
My headlamps, fan and water pump have fusible link at the relay load feed. While we're on the subject relays should be close the the load. Locate the feed for the load as close the the load as possible. No sense having all the relays in the interior controlling items far away.
Doug
 
I've heard conflicting opinions on where to place the relays also? So close to the device is the way to go?
Also, the cheap fuse block seems ok to use?
Thanks for the replies!
 
I've heard conflicting opinions on where to place the relays also? So close to the device is the way to go?
Also, the cheap fuse block seems ok to use?
Thanks for the replies!
When the relays are close to the load the amount of larger gauge wire used for the load is lessened, saving money and weight-it all ads up.
Mike
 
When the relays are close to the load the amount of larger gauge wire used for the load is lessened, saving money and weight-it all ads up.
Mike
True, to some extent....but the cost savings and additional weight of a larger gauge wire is insignificant. The cost of a change from a #14 awg to a #8 awg, assuming both length the same is: 10 ft is approximately $1.15 and the weight savings is approximately 1.25#. IMO not enough to worry about.
IF it were my application, I'd use the appropriate size wire for the intended load, with a 10% safety factor, switched by a protected relay, located as close as possible, space permitted, to the power source. The protection method would be determined by the importance of the circuit involved be it headlights, wiper motor or sound system, with a circuit breaker vs a fuse. The National Electrical Code, makes provisions for wire size, ampacity, and type of insulation used on the wire, as different insulation materials have different thermal ratings and different ampacity. The Society of Automotive Engineers (SAE) has guidelines to follow for automotive applications, depending on the criticality involved. If you need additional help in determiming wire sizes, drop me a PM.
BOB RENTON
 
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I bought an ARC Relay panel and ran a large cable through the firewall to it. Mine has four stations that I used for Power Windows, Power Top, A/C fan and an extra. I also converted the Amp Meter to Volt Meter and all the high amp items are now isolated. They also converted all fuses to breakers.
 
To the OP,

The headlight and the wiper motor power source should never have an in line fuse, period! Every car made by Chrysler had a hidden breaker, (20 amp for the headlights) and (5 amp for the wiper motor) in every switch as a safety precaution. How many times will a blown fuse "reset" while driving at night? If you are increasing the amperage load for the headlights, do the math and install a circuit breaker only with at least double the load capacity for the amperage draw. A four headlight stock from the factory draw was just under 3 amps per bulb with the breaker just under double the rating.

Jim


Thats true and them circuits still were powered through a fuseable link. Which is nice in case the the breaker would short the contacts together that circuit still has the fuseable link protection. Years ago when I worked at Ford in the 70's we would have them come in sometimes where the cust says after driving a bit the headlines would start flashing on and off. And they did as we could get them to do it in the shop and it usually ended up being the headlite switch as the breaker in it went bad. I would check the draw on the headlite system and it was usually normal and the switch would fix it. Ron
 
Where's your sense of adventure?
Mike

I lost that on a dark rainy night driving Hwy 1 (The coastal highway here in California.... Twisty turny road on the cliff along/200 feet above the ocean) when my headlights went out.... Pucker factor was very high... I was driving my 70 Challenger Convertible... The next day I added relays... Sense of adventure gone... Poof!!
 
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