[labreejr]

I'm finishing up the wiring in my 84 Cutlass. Still need to wire the power seat, power trunk release, led driving lights, led 3rd brake light and electric fan. Which do I need relays for & which needs a fusible link? I kind of understand now how a relay works, but still a little confused on fusible links. Thanx in advance.

[sunsetdart]

Rule of thumb is anything that takes lots of amps....use a relay. Things like electric fans, electric fuel pumps use relays. The other things you mentioned you can get away with fusible links.

[malc]

Fusible links

Relays

[aosborn]

They provide two different functions. Relays are a way of controlling a high current circuit without having to run all the current through a switch on your dash. A fuseable link is a circuit protection device like a fuse. Even with a relay, you still need circuit protection ie a fuse or circuit breaker.

Fuseable links are fine until they "blow" then they are a pain to replace. Fuses and or circuit breakers are a better way to protect a circuit. Self-resetting circuit breakers are a nice alternative when you have the space.

[75gmck25]

As aosborn said, relays and fusible links are for two separate functions:

Main power feed from battery or distribution point, high amperage draw (like 60-100 amps) - use a fusible link

Provide power to an individual accessory, low to moderate amp draw (up to about 30-40 amps), need to switch or control with a low amperage switch or sensor - use a relay
For example:
-- Use a main power feed from the battery (e.g. 8 gauge wire with 12 gauge fusible link) to a junction block.
--From junction block terminals use smaller gauge wires (10-16 gauge, depending on amp requirement) and appropriate size fuses to connect to each relay.
-- Use low amp draw switches (1-2 amp) to control each relay and activate the device.

Bruce

[justacertifiedtech]

Power Seat = You need to use a self resetting circuit breaker (SRCB)
Power trunk release = 10 amp fuse should suffice
Diving lights and 3rd brake light = If tied into existing vehicle wiring, will already have circuit protection in place. There is a SRCB integrated into your headlamp switch, and the feed to your brake lamp switch is fused.
Electric Fan = Needs to be wired with a relay.

GL,
Tech

[techron]

i agree with aosborn, circuit breakers all the way. circuit breakers are fuses that fix themselves automatically, fusable links are a pain in the (|)...

[malc]

Originally Posted by techron

i agree with aosborn, circuit breakers all the way. circuit breakers are fuses that fix themselves automatically, fusable links are a pain in the (|)...

You have to find and fix the problem before you reset a circuit breaker or repair a fusible link.
Having a circuit breaker does not simply anything.

From MadElectrical,

"Chevy began installing Fusible Link wires in the main-power circuits with ’66 models, and of those old cars that are still in use, most of the original Fusible Link wires are still in place. If a Fusible Link burned out then it saved the car!"