Hello group...I ride a recently-purchased '90 FLHTC bagger.  she has 32K on the clock and runs like a champ.  The previous owner added several lights to the rear of the bike that active as running/brake lights, and I am noticing that when I apply my brakes (front and/or rear), the voltmeter will drop substantially from 13-14 v to 8-9 v.  Additionally, I have noticed a pegging of the voltmeter needle at 0 when I spool up the starter.  This all came about about 2 weeks ago when i tried to start the scoot after sitting for about a week, and got NO action on the starter.  I put her on an overnight trickle charge, and the next day she started just fine.  There is a split-second hesitation when I depress the starter button before she turns over, and this is when I've noticed the meter peg to zero.  
I am thinking that there should be a relay in the lighting system to relieve the load of the extra lights, and am at a loss on the starter situation.  Any guidance on either or both issues would be appreciated. 
I'll be checking back in daily, so thanks in advance.   Chardagha

Hello,

First before we get to deep into analyzing the electrical system, my first two questions would be how old is the battery? And are we sure its still good?

You mentioned that the bike sat for only a week and you had no-go on the starter. That is not right at all and sounds to me like the battery is not holding it's charge. The symptoms you are seeing with the hesitation of the starter and the pegging to zero could definitely be caused by this.

As for the light issue. First thing I would try do is make sure it is the added lights causing the problem. Take the bulbs out and then see what happens. But first I would have the battery checkout out, that could also be contributing to what you are seeing here.

just logged in and happy to see your responses...can't believe that I didn't think to check the batt first. Will do now, and advise of results. Also like the idea of removing bulbs

You say its a 90, i would also take a look at the ground connection and make sure it has a good clean connection to the frame.

Good point slippery, I should have mentioned that. We see many bikes with bad connections on the battery or the frame ground that cause all kinds or intermittent problems.

Just as a reminder, a good inspection of your motorcycle should be done periodically, and anytime you buy a used motorcycle. This would catch problems such as a loose ground, dirty or poor battery connections, and many other things that could run your ride, or even cause danger to you as a motorcycle rider.

Here is a quick guide to a Basic Motorcycle Inspection

Hey Chardagha, Just curious if you ever figured out what was causing the problem?

It could also be a short in one of the extra lights wires.

hey group...I toyed with the battery for a while and finally replaced it with an "odessy" pc 680 mj battery.took her on a 150 mi ride today in the so. cal heat and she started fine every time. still concerned about the voltmeter pegging at startup, though.