quick H4 question, re: fuses & seals
 

I am putting in the H4 upgrade on a '73 and not sure what fuse to use on the power wire from the battery to the relays. I used a 3 amp fuse at first but as soon as I flipped the switch they blew. Then I went to a 5 amp fuse which worked fine for low beams, but when I flipped highs, it blew again. I'm off to get some higher amperage fuses. My question is whether I am just using too weak of a fuse? I'm going to try 7 or 8 amp... maybe higher. How high of a fuse rating can I use before it stops doing its job and my electrical system starts to get hurt?

Our host sells H4 lamp seals. I have the ones that go between the lamp housing/ring and the fender (kinda roundish with a rib). Are these supposed to be used with any model year? When I try it on, there's jus NO WAY that I am able to firmly secure the ring on the fender with the seal in place.

Thanks for any input.

I belive that I'm currently using 20 amp fuses with 30 amp rated equipment.

generally,
the load should be 70% of the CB/fuse

Re: quick H4 question, re: fuses & seals
 

Do you mean the wire supplying the coil of the relay (throught the dash switches) or the main power supply to the switched contacts of the relay (i.e. the feed to the lights when the relay is on)? If its the former, I'd imagine a 3A fuse would be more than enough unless you have a short. If its the latter, 3A or 5A probably won't be enough.

How much fuse you need is based on how much current you're drawing. If one wire supplying all the power for the lights (feeding all the relays), and you have 55/65W lights, you're drawing 110W through the low beams and 130W through the high beams. At 13.8V, this is 8A for the lows and ~ 9.5A for highs (P = IV). Get a 14A or 15A fuse.

More info on how your new lighting ciruit is wired would help.

Chris,
I was referring to the main power supply that feeds the lights; the wires from the battery to the relays. I have put in 10A fuses and they are holding for now. Just in case I am carrying 20A with me.

Guys,
Thanks for the formula for calculating the amperage on the fuses needed. That saves me a lot of trouble on asking a similar question when I increase the bulb power.

The way I wired them is generally following all the previous/similar threads about the topic. I put in 4 Bosch relays one for each beam (hi/lo/passanger/driver). 12 gauge wire for most of the wiring, 10 gauge for the main power from battery to the relays. The main power from the battery is split up into two leads, each is spliced (after the fuse, 10A for now, if traced from the battery) to power both passenger and both driver side relays. Hope that's concise enough of a description.

By the way, what's the most powerful bulbs I could use in there WITHOUT going to the hi power bulb sockets?

Thanks for the patience.

there has been melting and fires with stock sockets using 80w real bulbs on low.. I don't consider the PIAA that is supposed to give 80w of light with the current draw of 55w real bulbs..

I wouldn't go any hotter than 55/60's with the stock connectors. BTW. where are you guys driving that you need 80 or 100 watt high beams? Keep in mind 100 watt highs don't REALLY let you go 40% faster or see 40% farther than 60 watt ;)

Good luck,

Jerry M
'78 SC

I don't need 100/80w bulbs.. I need my 130/100w, LOL.
but doing 80mph on black interstates gives me time to avoid "gators" in the left lane with 100w low, no kidding. and 130w high thru the Rockys is relaxing. not to mention someone broken down in the right lane.. but for routine city driving it's not necessary.......Ron

The OEM plastic connector is safe with 100 Watt bulbs, and no actual socket is needed at all ... individual non-insulated Faston connectors can be crimped onto your wiring, even 10 ga, and it is perfectly safe to have them attached to the OEM 'sugar scoop,' H1, or H4 Bosch assemblies in your headlamp buckets! While attached there is no risk of shorting, and who is going to be removing them while power is applied?

Harlequin ... one fuse per relay would be the safest, and most reliable installation! Total headlamp failure is not a pleasant experience in the middle of the night, long ways from home!

Thanks for all the input. I'll be looking into whatever bulbs are out there, and adding two more fuses into the line up.

To add to what Warren said, and doing so with most humble respect to his seemingly endless knowledge of things Porsche, the heat that damages most connectors is caused by poor connection between the mating surfaces, not by the bulb itself. Make sure that the female ends are clean and tight and the mating bulb tabs are clean. You can remove the female connectors from the housing and pinch them slightly with a pair of pliers to tighten them up. As Warren said, if they're beyond help, you can replace them with crimp on connectors. If you do a search online, there are companies that sell OEM style headlight connectors with new crimp on spade terminals. If you're REALLY anal like me, you can crimp them AND solder them to make sure you have a solid connection. Good luck!