You might try to Google John Deer LT155 electrical system and see what appears.

I did, and found two as below but there are other differing diagrams for the LT155. The two below are similar, one being what is called the 3 amp system and the other, a similar 15 amp system.

On both, I do see headlights, but no tail lights, hour meter, or any other warning lights for that matter. There are lots of cut out safety switches however.

As for a switch for the headlights, it would appear that there is a key position that turns the headlights on, but I may be wrong in that as well. In any case, I did not see a specific switch in either of the drawings below.

I think you are going to have to purchase at least a voltmeter to get much further. I use a twenty dollar volt or multimeter with fair success; Fluke or Snap On are not required.

If I understand correctly, it appears that there may be volts to the headlights all the time and the key position just grounds the other side of the headlights to make them illuminate. As such, with a voltmeter, you might see volts on any of the headlight terminals. I am probably wrong on that however but a voltmeter will let you know.

Let us know what you eventually figure out.

Your father in law will really enjoy the ride; better than one of those "medical" units. On my 425, I made my headlights Wig Wag so that is something to aim for once you get them going.

 

Thank you very much. I spent a while last night googling but never did find what I was looking for.

I've needed a voltmeter for a while but this will give me an excuse to get one.

It makes sense what you say about the switch actually grounding out the headlights. Really they're not needed but him mentioning to me that they don't work and my habit of tinkering lead me to investigate. The fact that I couldn't fix it now has me on a quest to get it figured out.

 

Robert, My neighbor, right across the street has an LT155 that has a switch on the dashboard for lights ( I do not know the year, but around the same time I bought my L110). On my old L110 I had, the switch was in the ignition key cylinder and position was one back from the run position. So if you started the machine normally, spring tension on the key to run the starter, then release it to the run position......no lights. If you click the key back (counterclockwise) one click the lights would run. Perhaps yours has that system?????
Also, looked and neighbor's has no hour meter either.

 

I wondered that if the ignition key was also the headlight on switch, just how that would work. Cunning, those JD people.

Also I am not totally convinced that as I stated, some key position provided a ground path, but that was my read of the wiring diagram - sort of, and now that I learn of a "secret" key position, then maybe there is also a ground path within the ignition key.

This is getting interesting.

 

I think on the LT155 the lights were on whenever the key was in run position. I don't think they had the two position run no lights and run with headlights until the newer LT150 model that replaced the LT155.

As I recall the hour meter was an option when I bought my LT150. There is an open plug by the dash to plug it in on mine. I've had a SenDec I bought from Sears on mine since around the second year I had it.

 

I own 3 of the LT 155's.. 2 of them have the RIO switch & 1 does not have it..

I noticed both wirin schematics in post ##2 have the RIO but they r different..

on all 3 of mine the lights r on ONLY when the motor is runnin.. there is no light switch nor is there a IGN switch position to turn them on.. on all 3 the IGN switch has just 3 positions.. off.. run.. start..

all 3 have the 'Freedom 42' full time mulchin deck

 

That's the way his is. Through my research I've read on the later models (most likely the 15 amp version) the key was a 4 position switch. It was Off- Lights- Run- Start. So if you wanted lights you would start the machine and then turn the key to Lights. However I have his is not like that. It's equipped with the common 3 position key. So like others have said the lights automatically come on when you start the machine and they stay on as long as the machine is running.

The previous owner (87 years old) said he "unhooked something" because he feared the lights were draining his battery. The problem is this is a fairly simple wiring design and it's easy enough to access and I cannot for the life of me find the something that he unhooked. So that is telling me there's more to the story.

I was hoping that maybe disconnecting the lights on a LT 155 was common and that maybe it was something simple I was overlooking.

Thanks so far guys. We will get this figured out.

And thanks for the responses for the hour meter. Under the hood to the right of the battery there appears to be a factory stamped hole that is the size of an hour meter but none is there. I realize these were very cheap machines and John Deere stripped them down as much as possible to save money.

 

I guess there is no ignition light switch key position then.

Per below, I just did a Google using LT155 and came up with over 300 items.

A few of them were ignition switches and others the whole instrument panel which showed only three positions for the key.

There are also new headlight grills but I did not see any hourmeters. I would however suggest you email one of the eBay sellers who is a "tractor breaker"; they just might have one.

Your LT155 looks like it could be fun and also give your father in law a bit of an introduction to computers - he might like that - surfing the net for tractor parts.

john deere lt155 | eBay

 

LightsOUT, I talked to my neighbor about his and he did indeed ADD the switch for the lights. His was a constant "on" setup new from a JD dealer, not a big box machine. He said he didn't have any battery situations with his, but hated the idea of the lights being on all the time. From looking more closely at it, it's a nicer machine than my old L110. The tranny shows a K51 sticker and it is obviously longer between the steering wheel and seat than my old L. I'm not a big fan of the mulch only deck it has, but it has been cutting his 2 acres for about 13 years. His hood is broken at the hitch/pivot point and he removes the entire assembly to service the engine (wind took it too far back early on). The seat is original with only one crack, my L110 didn't survive that well at similar age and storage conditions. His had no slot I could see for an hour meter on the dash.
I think your dad will like it if you sort out the headlights. Just tell him he shouldn't be mowing in the dark:sidelaugh

 

Thanks for all the responses and interest. I didn't think I would get any bites at all. You guys have really gone out of your way for me. It's appreciated, believe me.

He really doesn't need the lights and he shouldn't be driving anything after dark! But it is bugging the crap out of me cause I know it's something so simple that I'll be embarrassed to come back here and tell what I found but I can't find it. I will though...

Another problem is it's not like I'm there every night. I only see him once a week for a little at best.