Another '81 cm400t lighting Issue
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  1. #1
    Junior Member ColdFore81's Avatar
    Join Date
    Oct 2019

    Another '81 cm400t lighting Issue

    Hey all, after reading through posts and discovering a lot about my semi-new to me motorcycle I've run into my own problem that has me stumped.. so I've created an account in hope that I can get some guidance on what I can do with these strange lighting issues I've been having.

    Anyways, I bought this bike a few months ago and have been riding it with no electrical problems until about a week ago, my running lights and brake lights went out on the road. Of course going through some of the posts on here led me to replacing the lighting relay, checking the fuses for continuity, and checking the direct wiring of the lights themselves (PO switched the tail signals with LEDS) I still have turn signals working in the tail, and when in park the extra license plate brake light from the PO works.

    I'm going to crack into the harness tonight, however the PO relocated everything under the seat without trimming any wires and pushed everything else behind the headlight in a bird's nest... so I'm concerned I might have pinched something on a turn, but upon first inspection it looks ok.

    After I write this up I'm going to go through with the multimeter and try to trace wires using a manual I found online and check the grounds for good connection. If anyone can recommend a good color coded wiring diagram I'd greatly appreciate it. The only thing I havent opened other than that is the brake lever to see if the wires going to it are corroded, only because the license plate light halfway works?

    One more thing, and I'm really kicking myself for starting something else before I finish another. I installed some of those LED turn signals on the front while I had the headlight off because I had a blown running filament on the old signals. Now that they're on and installed I've got running lights, but no turn signals on the front, giving me more of a headache. They're just cheap two wire amazon signals, so tonight I'll order another dual filament bulb and put the old ones back on, however it would be nice not to have to worry about changing bulbs anymore. The blown running bulb was like that when I purchased the bike, so I dont think that would cause other problems, right?

    Thanks in advance for any help you all can give me, and thanks for having me on the forum.

  2. #2
    Super Moderator longdistancerider's Avatar
    Join Date
    Oct 2011
    Vancouver Washington (text 408-239-9580)
    The brake light is actuated by either the switch on the master cylinder or the rear pedal switch which is located on the frame and uses a spring attached to the pedal. That one is adjustable whereas the front one isn't. You can jumper the 2 wires on the front one to keep the light on for testing.
    PM sent for the Honda FSM and color wiring diagram
    Be aware that with LED front turn signals there is the need for diodes to be added to the indicator bulb circuit. Personally I like the stock units because they're big, bright and easy to see.
    Jim O'Brien
    1979 CM400T "road bike" modified for travelling
    1978 CB400T1 restored
    1972 CL350 nuts and bolts restore in progress and
    Road Trip or "where's Jim now?"
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  3. #3
    Junior Member ColdFore81's Avatar
    Join Date
    Oct 2019
    Well I could get to work on getting into the harness due to some rain last night, but I'm here now in the afternoon checking it out. After reading a couple more posts about people having similar problems I decided I'd check under the fuse box for corrosion and what did I find... as soon as I took off the velcro the wire to the rear lights was so corroded it just came off..I know this is going to require a replacement, so I've opted to get a ATC blade type fuse box since 1.) I can have one here tomorrow and 2.) Itll be much easier to find and replace fuses in the future.

    I hope this will resolve my problem, but being that the turn signals on the rear were working, could this just be another problem to add to my list or is it possible I've hit it on the head? If I jump the connection together at the busted fuse box I still get turn signals, but no brakes from either the rear nor the front. Until tomorrow I am going to to clean up as much of the PO'S wiring as I can. Really starting to understand why this bike was such a good deal.

    BIG thanks to the above poster longdistancerider for setting me up with a manual, diagram, and all the PDF's I need to complete this maintenance journey.
    Attached Thumbnails Attached Thumbnails Another '81 cm400t lighting Issue-1570649436958571880044574381187_1570649453323.jpg  
    Last edited by ColdFore81; 10-09-2019 at 02:02 PM.

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  5. #4
    Member BlargKing's Avatar
    Join Date
    Aug 2019
    New Brunswick, Canada
    Nothing worse than buying a used bike and finding the previous owner added/changed/neglected the stock wiring. It can be done of course, but most people seem to lack the willingness or skill to do wiring properly.

    Contact cleaner and 400 grit sandpaper are my go-to for removing corrosion from connectors.
    1984 Honda CB450SC Nighthawk

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