My Daytona clone has a fiberglass aftermarket nose. The headlight doors actually lay back to expose the fixed headlights inside. When I bought it the headlight doors were vacuum operated, the problem being that after 45 mph the vacuum couldn't hold the doors closed. I removed the vacuum set up and installed electronic actuators with the rocker switch mounted on the dash. The main power runs off the feed that use to operate the power windows, so it's powered from the fuse block. Each actuator draws a max of 5 AMP's, I was planning on installing a 10 AMP in line fuse. A car buddy/mechanic is telling me I need to install a relay, that the in line fuse isn't enough. He said it's simple, just wire it like a fog light set up. I looked up the wiring for fog lights, it's not the same, with the lights you run one wire to ground. with the actuators you need to run both wires back to the switch, so you can reverse power to open and close the doors.
Spent an hour looking at relay diagrams, not an electronics expert so any input would help.

what do the instructions for the actuators say? You still need the proper fuse size for it. Relays are used so that you don't have to run as big wiring all over the place for high amperage stuff like horns and you can use smaller switches.
If you really want or need to use relays there are pictures on google that show how to do it that show the layout of the relay and what wire goes where.

10 amps added load is not a lot. The fuse box "should" handle it. That said, the OE system is marginal especially the power feed to the fuse block. The system would be meaningfully more reliable and safer with a relay pulling power directly from the engine compartment. You still need a breaker or fuse on the feed to the relay.. Normally sized at least 25% higher than the load. 15 amp fuse for a 10 amp load would be OK I think.

I agree and I would second using a circuit breaker for a "safety critical" circuit like holding the headlight doors up.

Fuses and relays perform two different functions in an electrical circuit and neither is a substitute for the other.

You would use a relay to switch a heavy load rather than a switch, but both need to be fused to protect the circuit.

Fuses are used to protect the circuit in case of a short.

Just to clarify the actuators only use power when opening or closing the headlight doors (approximately 4 seconds run time for each direction).
The wiring diagram from the manufacturer does not show a relay.

So you're saying the relay should be located in the engine compartment and be pulling power from somewhere in the engine compartment. I will continue my search online for a wiring diagram.
Thanks

Not saying you need a relay at all.

What are your switches rated for?

If they are rated to handle more than the 10A you are using then they are fine.

I bought the linear actuators and the switch from Firgelli Automation. The switch is rated for 16 amps.
I did find some more diagrams regarding the relays. I would need two, one for up, other for down.

WIth your switch rated at 16A when your load is only 10A and no mention of relays in the documentation you don't need them just the fuse. Use a 15A fuse. Even with the relay 10A fuse with 10A load chances are good it'll blow.

Don't forget more importantly than the expected amp draw and switch capacity, the wiring gauge and subsequent amp capacity is the other biggest factor in fuse size. The entire purpose of a fuse is to be the sacrificial component in the entire circuit so that it heats and burns first, not the wiring or the controls or powered source. Make sure your wiring is not a lower amperage rating than the fuse you choose.

A relay is a current reducer, a fuse is a circuit fail safe.

BTW, let me know if you need anything. I have spools of automotive wiring, fuses, leads, switches, etc. You're welcome to stop by and grab what you need.

I wouldn't call a relay a current reducer but rather a current shifter. It'll shift the current from the switch to itself, but it will do nothing to reduce the current the load needs, leaving only the current needed to operate the relay for the switch to handle.

Fair enough. Agreed! I oversimplified as my point was not to lose sight of the importance of wire size as well. I've seen a few times where people were shocked when their "fused" circuit smoked due to burning wire.

A relay is a current redirector, a fuse is a circuit fail safe.

Supercuda's got this nailed. Relays (unless being used in some kind of logic circuit) typically are used to increase the current handling capability of a circuit. If you have a circuit that draws 2 amps and a switch rated at 5 amps you're golden. If you have a circuit that draws 8 amps, you use the 5 amp switch to control a 10 amp relay and again, you're golden. You see this all the time on air compressors. Up to about 5 hp the pressure switch can handle the motor load. Over that you need a motor starter, which is nothing but a special purpose relay, controlled by the pressure switch to handle the increased motor load.

You might not need a relay but sometimes using a relay makes the whole system safer. For example, you can eliminate the extra current draw in the passenger compartment by wiring the switch to close a ground. Then use the ground to switch the relay. Closing grounds on the switch panel is safer than having a bunch of 12 volt wires running around under the dash.

This is exactly right

I'm busy now to read all replies, but sometimes relays like the 5 pins bosch are not installed to handle loads but just to switch the source from one place to another place when triggered, keeping the source active ( i.e. headlight doors on electric concelead headlight systems, where both posiions need to be energized. These are 4 prongs but just because ground is chassis ). Of course, the relay helps on the load issue at the same time