1982 XJ750 - Starting Issues

Hi all, first post here and I'm stumped!

I'm helping a friend get his 1982 XJ750 Maxim running again, after having sat for 10+ years in a barn.

The battery I'm using is older, but holding a charge just above 12V. It's a small car battery sitting next to the bike for testing. Bike is in neutral, kickstand switch seems to have been removed from the start circuit, as the owner doesn't ever remember there being an issue starting with kickstand down. We've also been testing on the center-stand, without any changes to our problems.

When I turn the key on, there's a small click from what looks like a 1.5"Wx1.5"Tx0.75"D relay, situated between the coils. I thought this was the starter cut-off relay, but there's also a relay below the reg/rec - isn't that the cut-off relay?

I've been following the "HOW TO: Test your starter circuit" thread (very helpful Gamuru, thanks!). I can short across the solenoid terminals, and the starter motor cranks the engine (no spark, however). In step 2, it says to measure resistance between battery negative and engine case. If you get 0 resistance, replace the starter. I have basically zero resistance when doing this test, but the starter motor seems fine?

Going through step 3, I can get the solenoid to click, but it doesn't want to turn the starter motor. When I touch the leads to the battery, I lose all power to the bike, and have to readjust the jumper clamps in order to get power back to the bike...not sure what the heck that's all about.

Step 4 - checks out all good, so it looks like the start switch is good.

Step 5 - I don't have 12V to the red wire at the harness pigtail for the solenoid. I believe this red/white-stripe wire goes to the starter cut-off relay, 4U8-00, located just below the regulator/rectifier. Does this sound right? I checked continuity between the red/white wire terminal at this relay and the red/white wire at the solenoid pigtail, and I had no continuity. Isn't this the starter cut-off relay? Maybe it's the headlight relay? He did mention the headlight cut-out the last time he rode it years ago.

Also, we've only got power to three of the four fuses under the seat. These fuses aren't mounted as they were from the factory, so it's difficult to say what each fuse is for specifically.

What is this white/red-stripe wire for, located near the solenoid? It doesn't seem to have a mate in the area.

Thanks for reading folks! This has been driving me nuts all week! I only have access to the bike here and there in the evenings. It's at my friend's farm, and he's only around every now and again (lives in a different state).

 

Here's a picture of the...relay?...under the tank, just to the rear of the coils. It clicks on/off when the key is turned. What is this for?

 

Battery sense for Atari and was mainly used to notify operator battery fluid level was low. Won't affect start / run operation but will cause warning light and BATT to display on CMS

Need to find out which one is missing power, which can be done by wire color - really you need them all so updating to a blade fuse box would be a good idea

Not sure what you mean here but if you are touching the solenoid wires to the battery and it clicks, but the starter does not engage then either the starter, solenoid, or associated wiring is bad. Since you got the starter to turn then the solenoid high current contacts are not connecting so it would be labeled not working

Flasher Relay

https://www.xjbikes.com/forums/threads/the-ultimate-relay-switch-sensor-and-diodes-guide.27543/

If you have a Seca, the Maxim is different but can also be found in the above link

"1981-83 XJ750 Seca and XJ750 Euro models:

Flasher: near the steering headpipe, on right side frame rail, under the right side ignition coil.
Flasher canceller: under the rear of gas tank.
Starter motor solenoid/relay: attached to and behind battery box.
Starter/Ignition cut-off relay (no color): behind coils, behind self-canceller.
Sidestand (kickstand) relay (blue): frame bracket outbound of LH frame tube, just behind the left side ignition coil.
Headlight relay (yellow): behind the left frame side cover, on the plastic regulator-rectifier mounting plate.
Diode block: inside the headlight housing.
Neutral switch: in a hole in the bottom of the crankcase, just "outside" of the oil pan, on the bottom of the engine, up inside a recessed "well"."