relays wiring

[westy64]

Hello,

I want to relay the following items (one relay per item)
low beams
high beams
halogen high beams
starter
fuel pump

horn and engine fan are already done (not by me).

do you think I have to put one power line (10 or 11 gauge each) for each of the relays from the alternator or the starter solenoid stud, or can I use the same wire for all the lights, for instance, then another one for starter and fuel pump ?

regarding the high and low beams lights, I plan to feed back the original fuse box after the relay.
do I need extra fuses before the relays ?

thank you for your help.

jean

[vandor]

You need to add up the amperage for each of the items, and then see what gage wire you need for that amperage.

I would not add extra fuses for the headlights, it's just another thing that can fail. Most of the wires in the car are not fused...

[RRoller123]

The AWG wire gauge current capacity chart here is very useful, a single 10awg feed from the starter/alternator should be fine for the lights. 2 lights at 55w at 12vdc = about 9 amps.

http://en.wikipedia.org/wiki/American_wire_gauge

[azruss]

If you bring your hi amp from the starter or alt thru a relay to its final destination, you have no amp protection. A short in that circuit will fry all the wires, melt all the wires next door, blow your battery up, and burn your car to the ground and the fuse in the relay circuit will do nothing to protect it. Your call.

[westy64]

thank you,
I will fuse the starter relay
lights are already fused
the risk of a short between the starter stud and the relays panel (inner fender) seems very low to me.

[vandor]

>the risk of a short between the starter stud and the relays panel (inner fender) seems very low to me.

Agree, IF properly routed/double insulated/common sense used

I had aftermarket fuse holders try to catch on fire, so I am not keen to add cheap fuse holders.

[westy64]

Agree, IF properly routed/double insulated/common sense used

I will specially work on route and double insulation.
Common sense : difficult, if you keep in mind I bought a 70's fiat.

Jean

[RRoller123]

Remember that if you interject a relay into the lighting circuit, the existing fuse for the lights only protects the trigger circuit, not the power circuit you will add that is going to the lights. In general it would be a good idea to fuse these power feeds, imho. But set the fuse values carefully. I miscalculated on my high beams and ended up suddenly in the dark at night on a back twisty road at 50mph. Fortunately I had set the low beam fuse value correctly and they worked to get me home.

[azruss]

the modern 2 prong fuse seems to be very reliable. I would look for a block set that would house 4-6 fuses and run everything to that. like Csaba suggested, no cheap in-line fuses. this is the achille's heal of this system.

[westy64]

Remember that if you interject a relay into the lighting circuit, the existing fuse for the lights only protects the trigger circuit, not the power circuit you will add that is going to the lights.

My idea is to link the 87 plug to the lights loop, at the original fuse.
I do not add a power circuit going to the lights.
I only "superpower" the existing circuit, originally fused.

Protecting the relay could be done with a 2 in 1 item like this ?
http://www.classicautoelec.com/relais-4 ... sible.html
Could no find which part of the relay is fused with this....

To be followed.

[RRoller123]

I think that would work, but the physical wiring is probably a lot easier if you break the feed to the lights up on the driver's side firewall and run a new short feed up to the relay from the alt to there. Post some pics when you get it done, I would like to see how this approach works out! At any rate, doing this brightens the lights amazingly! I didn't even bother with a halogen upgrade to the bulbs after wiring in the relays, the lights were plenty bright enough! On a side note: The unit from Daniel Stern that will allow our front side markers to operate as both DRL and turn signals is a really nice upgrade, and enhances the safety of the cars a lot imho. Combined with brighter side marker bulbs, it is well worth doing.

[westy64]

My alternator is on passenger side, so I will take the feed from the starter stud (junction alternator and battery).

Here is the modified diagram.
Sorry for the missing details about the relays :



Doing this way, I just have to go through the firewall once, to feed the circuit after the relay.
I can wether go straight to the fuse box (direct route), or following the big harness (close to the ignition switch).
Not decided yet, but I feel lazy on this one, so the straight route might be my preferred one.

[azruss]

I dont see any need to take the wiring back thru the firewall. Use the existing circuits to fire the relays. mount the relays under the hood along with a fuse block. run your big wire from the starter lug to the fuse block. then from each fuse to relay mains with smaller wire appropriate for that specific load.

[westy64]

I dont see any need to take the wiring back thru the firewall. Use the existing circuits to fire the relays. mount the relays under the hood along with a fuse block. run your big wire from the starter lug to the fuse block. then from each fuse to relay mains with smaller wire appropriate for that specific load.

just because I don't want to change much the look of the wiring harness.

<Use the existing circuits to fire the relays>

Existing wires don't go from the light switch to the relays area.
After the switch, they go to the fuse box.
After the fuse, one goes to front right, and the other to front left.

As I only want one relay only for each function, I will use the wire after the light switch to trigger the relay.
And I will then feed the existing circuit at the fusebox.
I understand I could do it other ways, but this way seems the less noticeable to me.

[azruss]

does this mean you are planning to mount the relay under the dash? I have considered that, but there is so little room under there.