Hooking up many relays

[A70Runner]

I am going to be hooking up a few relays on my car. Headlights, Radiator Fans,Fuel Pump, and probably a fan on the Trans cooler. Two questions. Where is everyone hooking to ( I know not the battery) and is anyone using a central add on hookup point?

Hope this makes sense.

Thanks!
A70

 

[rmchrgr]

I would suggest using an MSD solid state relay. It has provisions for four devices and is run off one power wire. The triggers can be on the power or ground side. Yes, it's a bit pricey but it will save you a lot of hassle. I use them, they are a nice product.

MSD Solid State Relay

On the fans and trans cooler you'll need thermostatic switches to trigger the relays.

 

[radical rob]

Either that or a small separate fuse block fed directly from the battery, that would let you fuse each circuit

 

[Sixpactogo]

I fed my fan and headlight relays with a #8 wire off of the Alternator stud. Been working fine for 6 years.

 

[RJRENTON]

I am going to be hooking up a few relays on my car. Headlights, Radiator Fans,Fuel Pump, and probably a fan on the Trans cooler. Two questions. Where is everyone hooking to ( I know not the battery) and is anyone using a central add on hookup point?

Hope this makes sense.

Thanks!
A70

When I learned electrical system components, there were two types. IEC International Electrotechnical Commission (IEC) for electrical relays, focusing on functionality, safety, and performance. And NEMA (National Electrical Manufacturing Association). The trend now is to use the light weight IEC components or the industrial NEMA rated stuff. The IEC stuff is maximum amperage/time rated where as the NEMA components are horsepower rated. My preference is the NEMA stuff as it's heavy duty and the IEC stuff looks very light duty rated. There is a significant night and day difference between the two types, with the IEC stuff is cheaper. Just my opinion.....circuit design differences are similar but maximum amperage ratings are different, especially with relays...Both types are available on line and thru ebay...
BOB RENTON

 

[gkent]

The solid state are nice but this one allows relay and fuse replacement

 

[T2R9]

The solid state are nice but this one allows relay and fuse replacement

View attachment 1898428

This is the one I use. Very nice setup.

 

[72RoadrunnerGTX]

If running a stock ammeter-based charging system, never connect loads at the battery or anywhere on the battery side of the ammeter. If not wanting to connect directly at the alternator stud, you can use a simple stud mount near the bulkhead connector, land the alternator feed on it and run another wire through a grommet to the ammeter, by passing the troublesome Packard bulkhead terminal for the alternator to ammeter feed. Load placement matters.

Alternatively, you can use a stud passthrough and connect the new alternator feed from inside of the firewall. Both approaches require a hole in the firewall be created.

 

[Crackedback]

On OEM ammeter wired cars... With items that run in both engine on or engine off state, there is no perfect place to pull power. You have to make a choice and go with the pickup point that the accessory will run most of the time, usually engine running.

 

[72RoadrunnerGTX]

Of the items listed by the OP in the first post, which would you consider would not be in use most of the time while the vehicle is in operation, engine running? Other than convertible top pumps and station wagon rear gate window lift motors, what other types of accessories are you referring to that would be better prioritized for operation while the vehicle is at rest, engine not running?

 

[gkent]

Other than those which are "factory wired", the only things I can think of that would need full-time power would be the fan(s) and waterpump (if electric). Everything else would be run off "keyed power". That said, it doesn't mean that other accessories need to be run through the ammeter. You can use relays connected to full-time power but triggered by the "key on" power. The relays draw next to nothing and are not a significant load through the ammeter.

 

[72RoadrunnerGTX]

Other than those which are "factory wired", the only things I can think of that would need full-time power would be the fan(s) and waterpump (if electric). Everything else would be run off "keyed power". That said, it doesn't mean that other accessories need to be run through the ammeter. You can use relays connected to full-time power but triggered by the "key on" power. The relays draw next to nothing and are not a significant load through the ammeter.

Not talking about the 160 milliamps it takes to trigger the primary side of the typical Bosch style automotive relay, referring to the unswitched high current load secondary power source, it does matter where this power comes from with a stock ammeter-based system. Running loads need to be on the alternator side of the ammeter to not add current stress to stock wires/components not designed to handle the additional current and not to defeat the accuracy and purpose of the ammeter to only monitor battery charging/discharging current.

 

[rmchrgr]

The solid state are nice but this one allows relay and fuse replacement

Electromechanical relays will have a higher rate of failure than a solid state part since they have moving parts inside. Probably not an issue on a weekend toy car but it's just something to be aware of. That black MSD one is also probably 3x as expensive as just buying 4 parts store relays. It looks cool though.

Again, with the SSR there's only one power wire. The OP is asking where to pull power from for multiple devices. In that same context, only having to run one wire to energize everything is way easier than running four separately-fused B+ wires.

Also, IMO, with the added constant, high-amp loads being planned, the OP might consider bypassing the OE ammeter if he hasn't already. All the current in the car passes through those gauge contacts so if there's enough resistance somewhere you will start melting stuff. Sure, under 'normal' circumstances and/or with an OE-type restoration with good wiring the ammeter is fine but it is a bit of an arcane design as ammeters have been gone from cars for almost 50 years. That' just this writer's opinion so take it for what it's worth, not trying to start a discussion about it.

Another suggestion here would be to upgrade to a modern Denso type alternator to keep up with the added current demands.

 

[72RoadrunnerGTX]

Also, IMO, with the added constant, high-amp loads being planned, the OP might consider bypassing the OE ammeter if he hasn't already. All the current in the car passes through those gauge contacts so if there's enough resistance somewhere you will start melting stuff. Sure, under 'normal' circumstances and/or with an OE-type restoration with good wiring the ammeter is fine but it is a bit of an arcane design as ammeters have been gone from cars for almost 50 years. That' just this writer's opinion so take it for what it's worth, not trying to start a discussion about it.

Will have to disagree that opinion, “All the current in the car passes through those gauge contacts”, fact is, as stock, while in normal operation, no vehicle loads are routed through the ammeter and related connections. If added loads are correctly loaded on the alternator side of the ammeter as are all factory running loads, there should be little to no current flowing the ammeter. True, battery reliability has improved at the same time automotive electrical demands have increased, the industry has moved on to newer cheaper technology to monitor if the charging system is functioning or not, doesn’t mean you can’t run some added loads and keep a stock safe functioning ammeter if loaded correctly.

 

[Nacho-RT74]

If running a stock ammeter-based charging system, never connect loads at the battery or anywhere on the battery side of the ammeter. If not wanting to connect directly at the alternator stud, you can use a simple stud mount near the bulkhead connector, land the alternator feed on it and run another wire through a grommet to the ammeter, by passing the troublesome Packard bulkhead terminal for the alternator to ammeter feed. Load placement matters.

View attachment 1898477

Alternatively, you can use a stud passthrough and connect the new alternator feed from inside of the firewall. Both approaches require a hole in the firewall be created.
View attachment 1898480

I have some prefferences for this design…. If just they weren’t soooo large:

3/8" Thru-Panel Studs - Bulkhead Terminals Through Panel Battery Terminals Connectors Junction Firewall


I think 1/4” stud is pretty much enough for our cars application. Dunno if does exist similar design into that size.

 

[gkent]

I use that bulkhead terminal. It's big biu I run a #4 cable in and out of it.

Fwiw - that MSD relay pack on needs a single + input as long as you trigger with grounds.but I trigger two with grounds and two with +.

 

[ynst]

I use that bulkhead terminal. It's big biu I run a #4 cable in and out of it.

Fwiw - that MSD relay pack on needs a single + input as long as you trigger with grounds.but I trigger two with grounds and two with +.

...and the MSD relay package easily allows you to switch to a positive trigger by simply removing the buss bar between the power feed and the relay pick terminal and grounding the other terminal.

remove the nut between the two relays and remove the two screws adjacent to the nut. If you only want one relay to be positively triggered, break off one side of he buss bar then re-install the buss bar and nut. Screw down the remaining end of the buss bar.

If you want to have both relays positively triggered, leave the buss bar off entirely.

This leaves you with a pair of screws and one will need to be connected to ground and the other to your switch to operate the relay.

I like to keep these relays inside the vehicle to prevent corrosion as most of my customers actually drive their cars and an under-the-hood installation isn't exactly good environmentally protected.

I've installed quite a few of these for folks and they've been very reliable.

 

[kiwigtx]

I'm out.