1981 seca 550 lights dim while riding and then shuts off

Hey everyone,
I'll start by saying I haven't posted to this site before, but old threads have helped me troubleshoot more than once, so thank you all.
I'm currently having a very strange issue with my 81' seca 550,, where I'll have good power at start up, bike fires up perfectly, starts riding just fine,but after about 5 min of riding I will notice the lights begin to dim when I'm off the throttle. During this time of minimal dimming once I pick up the throttle again the lights brighten, but the issue quickly worsens until the gauge lights and headlights are very dim and then the bike shuts off, as if I have no power and the battery is dead. But the strangest part is that after letting the bike sit for 5-10 minutes, I turn the key, and power is beginning to restore, and it will start back up. After a short 10 minute rest, the lights will start dimming when off the throttle almost immediately, if I let the bike rest for an hour + it will act like it did when I first started it.
I've been battling this issue for awhile, checking anything that I could think of as being the problem. The rectifier and battery are not hot, and everything checks out that I could think of. Hopefully one of y'all can help
Thanks

 

Welcome to the forum. Have you checked what voltage you are getting at the battery from the alternator?

 

I have no put a meter on it, which I really should have already. Im was just so confused how I can have symptoms of a dead battery, bike shuts off, but after sitting for a couple minutes the power seemingly shows back up.... And when I tell u that when it shuts off it's as if I have no power, I mean almost nothing. Yet there is actually power there...... I'm wondering if it's something going on with the battery itself, and even tho the battery isn't hot, it's hot enough and I have a dead cell or something.

 

Thank you for the welcome. I may be new but I've read over countless threads over the years and feel like I already know many of u guys.

 

With the bike in a failed state starting with the battery is a good starting point, but measure directly on the battery terminals and not the attaching cables.

If OK, then move the leads to the battery cables.

If that is OK, move the black lead to an engine ground and positive on the battery plus to verify a good ground connection exists.

If OK, then move the positive lead to the output of the main fuse to verify a good connection. If you don't know which is the output just check both sides

If OK, then check power that would be routed through the ignition switch back to the other three fuses in the fuse block

Note during the process keeping a load on the system might help keep it in a failed state and aid in troubleshooting. Normally, the headlight would stay on until the key is cycled, but it may drop out if one of those above connections heats and drops enough voltage. Therefore, you might want to keep the front or rear brake on during the process to keep a load on the system

 

Thank you for ur time and response,, I've been doing a bunch of tests over the last couple days, which prove to be difficult to test during the time that the bike begins acting up. I've actually come across a few other posts on various sites after searching for 81' seca 550 overheating that people have had a similar problem, that the bike runs for a few minutes before the headlight begins to go dim when off the throttle. The light gets bright as normal again when on the throttle but after a total of about 10-15 min of riding, letting off the throttle will cause the head light, cluster lights, every light to dim to almost night and the bike dies seemingly to have a dead battery. After letting it cool for 15 minutes, and I turn the key, the neural light is bright as can be, and bike fires right up with a bright headlight, cluster, tail light, but after riding again the process repeats, only even faster because the bike is already up to temp.

Rectifier and battery are all that I can think of.

 

Well 15 minutes would seem like plenty of time to make those measurements, or at least get the battery voltage??

But, that said, what is the condition of the fuse block? Have you replaced it? Is the main fuse getting hot?

Have you cleaned and inspected the grounds - battery cables, frame to engine wiring the 550 uses, the main ground under the tank at the ignition coils

If you lose the connection at the main fuse the bike will basically run on the voltage generated from the alternator. However, that has its limits and when the RPM drops near idle it may not produce enough voltage to keep the bike running without a main fuse connection to supply the needed boost from the battery. The low voltage would dim the lights and the bike would stall, and it will continue to exhibit low voltage until the connection cools and the voltage loss is reduced

The Seca has a built in voltmeter, what is it reading when good vs bad?