Schurkey's post back a few pages back got me thinking about all the relevant ways this mod can be done. I don't know if I have the quote feature working here so here's a link:
https://www.gmt400.com/threads/4-hi-headlight-mod.122/page-47#post-989084
I also like Daniel Stern's piece about upgrading the circuit with relays.
http://www.danielsternlighting.com/tech/relays/relays.html It's interesting he says there are different U.S. and European ways of stating rated bulb
life (he says it's at 14.0v for U.S., not 13.2v ... I highly suspect the truth is somewhere in between those two figures but I'm not going to research H4701 or H4703 bulb tech sheets to find out.) << Mine's an '89.
So right there, your questions are:
1) What's my alternator doing? (A commonly-cited voltage in most vehicles is around 13.8v as being, well, common.)
2) How much of whatever that is, reaches my headlights?
3) What's considered safe, or at least a good compromise between longevity and lumens?
If a certain voltage number is too high for bulb longevity, manufacturers would seem to be building intentional resistance
into the design with the happy outcome of being able to spend less money on 18ga is a bonus for all. So long as heat isn't a problem, all is well. But that leaves no wiggle room for corrosion and failing connections. But it also assumes that the full power from the system with engine running is too much. Maybe it's not.
Your wire gauge selection hinges on all of that PLUS the length of the runs. Measure voltage drop, but remember that if you're seeing massive voltage drop with a stock setup, it
could just mean your stuff is corroded (but where? at the bulb harness or bulb ground?), not that the original design is "weak" per se. In other words if you
overcompensate with huge cable/fresh bulb sockets don't be surprised if your lights burn out fast. Depending on your system output LOL.
At a hypothetical 13.8v, an 18ga wire only needs to pass 4A (per low beam headlight) to deliver 55W
if kept to a few feet. It's easy to see why so many people use thicker wire. But consider: a relay at the very front of the truck is only about 2-6 feet from any light.) Are we having fun yet?
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Even the simplest, 1-relay method would seem to help the Low beams with a power injection of sorts midway in the circuit. But I'm more drawn to the 2-relay method(s) since the Hi side would also be helped.
I also like the 2 relay method Great White mentioned, where the Lo side is triggered from the yellow switch wire near the dash switch, even though I'd prefer not to have to run another wire through the firewall. But I might go that route (no pun intended) since it eliminates the diode otherwise needed in a 2-relay setup and has the other benefits he mentioned.
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I'm settling on these:
Hella H84989011 relay socket
Relay sockets allow you to pull the relay if there's a problem without also unmounting the support since the flange and hole are part of the socket and not the relay. And it's a little neater-looking since the bolt is hidden.
Hella 933332151 5-pin relays with dual 87 taps (NOT the more common "87, 87a") allow you the option of running individual power wires to bulbs and alleviate some stress at the relay since it'd be just one electromechanical contact per bulb. Reliability improvement?
I really wanted to stick with Hella or Bosch, partly because I can track down and the cross reference part # later when replacing. Can't do that with generic or no-name stuff as easily.
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Still on the fence about replacing the bulb harness connectors/running wire directly to them. Like I said, part of that voltage drop consideration depends on where the relays are installed.
And yes, neatness and lack of complexity counts for something here. I'll do a voltage drop test and visual inspection meanwhile.
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