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Somewhere there was a post on rewiring older Alfas to put in relays. It talked about the headlight switch, fuel pump, and ignition switch.

My question is what gets a fuse? The high current circuit, the low current curcuit, or both? Where does the fuse and relay go? upstream, or downstream of the equipment being operated?

eg: headlights, what's the standard?

Power source to fuse to relay to lights to ground. or,

Power source to lights to relay to fuse to ground?
 

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Richard,

Fuse everything.

Good news is that the original circuit, say for the headlights, is re-used as the low current activation circuit for the relay, so the factory fuses and wiring can stay intact. I'd strive to reuse this wiring as-is and not cut anything, so you can quickly return it to original specs if required.

Your 'new' circuitry, which is now the heavy current power supply circuit for the end components (lights, fan, horns etc) should be fused as close as possible to the power supply.

Easiest and neatest way to do this way is to buy a modern, aftermarket blade-fuse holder that powers all the fuse positions from a single point. Situate this fuse block nice and close to the battery or starter (wherever you want to take the power from) and connect a heavy gauge wire to the connection on the fuse block. From here, run individual wires of the required gauge to each relay or component, then slip in a fuse just adequate for the task.

Having in-line fuses randomly spread all over the car makes later troubleshooting a real pain in the bee-hind, and having everything situated in one fuse block is a godsend when you are stuck on a roadside in the rain at night !!!

I recommend you purchase a quality wire crimper and use quality crimps.

Don't forget to make good earths as well.
 

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There’s a good description of how to rewire headlights for any car here http://www.danielsternlighting.com/tech/relays/relays.html . You tap into the wires which go to the headlight plugs to get the switched high and low beam positive to switch the relays on. You need one relay for low beam, and one for high beam. The best way is to see if you can get a second set of headlight plugs from a car wrecker, and that way you can just unplug the old plugs from the headlights, and leave them unplugged, and plug in the new relay-switched headlight plugs to the back of the headlights. In the USA and Australia, and probably plenty of other countries, you can buy ready wired headlight looms complete with relays if you can’t do it yourself – they usually plug into the original headlight plugs. Here in Australia, 4WD equipment suppliers can usually supply these.

As Beatle Bayley says, you really need a good quality crimper – the best ones are the ratchet ones, which always provide a decent quality crimp, like these http://www.altronics.com.au/index.asp?area=item&id=T1552 . They cost more, but as an electronics technician, I found that normal plier type crimpers regularly didn’t provide reliable crimped joints, whereas since I bought a set of ratchet crimpers I’ve never had a failure crimping automotive type insulated terminals. They’re also much easier to use, since you need less hand pressure to crimp, and they always supply the right amount of pressure.;) The only way to get reliable connections with the cheap non-ratchet crimpers is if you solder the connection as well as crimping, and because they are often too narrow, they leave you with sore dents in your hands!:mad:
 
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