Headlight voltage

Actually, it'll handle at least three, I've seen production locomotives with three bulbs on the headlight circuit.  I suspect it'll handle even more, but why push it.

LocoSound has 6V bulbs, but older steamers with the DCRU and horn board run the headlights from track power, they're typically 14V bulbs.

You have to be specific as to what model you're talking about.

MTH recommends no more than two in the upgrade kit instructions, but as John says they do run 3 on some production diesels.  F and E units.

PS-1 Steam used 18V headlight since no control wire from PS-1 board.  Tender light was 1.5, if the engine had CV board lights would be 6V standard.

Loco Sound used all 6V.   G

John & George, thank you for the answers. 

I'm using a PS2 upgrade kit to upgrade a circa 2001 Mohawk from 5-volt to 3-volt, and putting the board in the tender.  Besides the headlight, there is a cab light and a firebox light.  It's easier if I don't have to try to fit LEDs in the grommets or in place of the sockets holding the bulbs.

The loco-sound engine is a 30-1663-0 Y6b, that I got this past York and am going to install a PS3 steam upgrade kit when I finish the Mohawk.  Haven't opened the loco body yet.

Typically the cab and fire box are a single plug double bulb light.  Should work fine just need some rewiring.  You can't get the PS-2 3V in the boiler?  G

I'm with George, try to fit the 3V board in the boiler.  I've had to extend the harnesses doing that at times, but it's a whole lot easier than doing the full upgrade kit to replace a set of boards.

To me, it turned out to be a lot easier to place the board in the tender.  No need to shoehorn, make a new heat sink, alter sockets, cramp wiring, etc.  Far from being too short, the harness cables were too long and I removed a section of wires between 1o-pin socket and individual 2 pole plugs.  Since I use Digikey supercaps, which are much smaller than batteries, space in the tender is not an issue.  But it's a matter of upgrader preference, so I'm

In the Mohawk, cab and firebox lights have separate plugs. 

I finished a K-4s just before the Mohawk, and it's interesting to see how MTH uses substantially different layouts and drive systems in similarly-sized locos.

You had independent control of those lights, and now you won't.  So it is preference on how you operate.  G

That is true, but in the 12 years I've owned this loco, I don't recall ever having turned the cab and boiler lights off.  As your say, that's operator preference, which in my case coincides with upgraders preference.  If I were in your shoes, doing upgrades for clients, I also would want them to have all the features available.