Headlight Relay Replacement

[eblanken]

I've been slowly working on my 1980 XS400s over the winter/spring and we are almost done but now the headlight seems to not be working. The problem seems to have been traced to the relay. There is power at the fusebox (new, blade-style) and if we bypass the relay we can get the light to turn on. It's a basic sealed beam. Nothing fancy. Not LED.

Here's the question: If the relay is bad (it seems to be), is there a MODERN relay that we can go buy to replace the original? It's a pain to find parts locally and I am REALLY tired of not being able to ride this thing. Does anyone have a modern setup? If so, can I get some info on what you bought (brand/part #, etc) and whatever else you may have had to do to get it all working.

Any help from you old-timers or XS lovers?

 

[arfstrom]

With out knowing your previous situations. That relay is only designed to work when the stator is energized. So if your bike is not running yet, don't worry about it. There is a thread where bbs360 and one other had dissected a relay. My assumptions was the white wire from the stator was to add power to the head lights. It was determined that line was used to open the relay to let power go to the headlight. I want to assume there is nothing wrong with yours.

 

[arfstrom]

I remembered a conversation(Thread) from a little bit ago. We went deep into both diodes then. It's 4 pages. I seem to remember that one of the respondents had taken apart the diodes/relays.

http://www.xs400.com/threads/yet-another-charging-issue.13139/

 

[BBS360]

I hadn't actually seen that thread. Skip ahead to post #76 for the relay internal photo and diagram showing the diode. Post #77 has the solution required to modify any universal automotive relay. Rugbywarrior also suggests that a latching relay could be found instead of the DIY modifications.

To summarize:
The diode in the relay serves two purposes.
In one direction it blocks the pulsed DC from the white wire from entering the pure DC part of the electrical system and in the other direction it maintains the relay coil, keeping the headlight on after the initial pulse from the white wire.
The diode in the wiring harness acts as the half-wave rectifier for the initial pulse to the headlight relay and it also blocks the headlight circuit's 12VDC from backfeeding the stator winding.

 

[arfstrom]

I thought that was what I said? Ohh that was in another thread, don't mind me