Tach/charging problem

[Phare Est]

I've got a tach problem and evidently a charging problem on my '81 XS1100 Midnight Special, since my brand new battery drains fast. The tach needle does not move and the tach lights do not come on (except for the Neutral and High Beam lights). The tach used to work sporadically (usually when I revved the engine up for a few minutes while driving the bike), but now it never works. At this point, I'm not sure if it's an alternator or a reg/rec issue (or a possibly wiring issue). I cleaned all the plug-ins behind the fuse box and the two reg/rec plug-ins. The headlight and speedometer lights work fine.

Here's the interesting thing. When I hit the brakes or turn on the signal lights, the tach needle starts moving; it goes up to about the 1000-rpm mark. What would be causing this problem?

[BA80]

I think you may have 2 separate problems. Work on one at a time and you may fix both.

The turn signal/brake light thing may be something in the headlight bucket plugged in wrong. There are 2 square 4 prong plugs in there that are the same but different colors. One of those plugs is for the tach.

[TopCatGr58]

Yeah,

Some of the plugs in the headlight bucket could be miss matched. However, they wouldn't necessarily keep the bike from charging. Aside from the 3 white connectors behind the fuse panel, if the bike isn't well grounded, it can also cause problems. There is the main battery negative to frame ground strap point, but also the engine to frame strap at the starter motor. Also, the REG/RECT and the harness wires all ground thru the bolt and frame contact holding the Reg/Rect to the frame. Inspect and clean all of them.

Diagnostic steps, running bike, single thin feeler gauge against ALT housing, should stick to it on outside. If not, then the Field coil isn't generating a magnetic field. The manual explains basic meter tests for the R/R. A quick check is to use a jumper wire and temporarily ground the GREEN wire that goes to the field coil, that will send FULL 12 Volts to the field coil, and running the bike should then generate the ~14.5V at ~2500+ RPM, if still only 12 or less, AND you still can't get the feeler gauge to stick to the outside, then the field coil is shot/shorted. But if you DO get full charging power, then both the field coil and the ALT windings AND the Rect part of the R/R is working, but apparently the Reg part isn't functioning...it controls how much current from the field coil gets grounded which controls how much power/amps is generated by the ALT.

Good luck.
T.C.

[Phare Est]

Thanks to BA80 and TopCatGr58 for the advice ☺. Both problems have been solved. It was a simple wiring issue: I had to fiddle with the three white wires going from the alternator to the REG/REC (by bending them in a certain way) for the tach to start working and for the battery to charge again. I tested the battery with a multimeter by revving the engine, and the charge went up to 15 volts.

As for the tach needle, it doesn't start moving for no reason anymore when the brake light or signal lights are on. The previous owner has done a bit of rewiring behind the fuse box, which may explain the tach needle's weird behavior when the battery wasn't charging. Anyway, I'll probably have to change those three white alternator wires sooner than later before the charging system starts acting up again.

[XJOK2PLAY]

Those 3 white wires and their connector are a common fail point.
More tachs have been fixed reworking those connections when they melt than anything else.

I dunno it for sure, but I suspect that either those connectors get corroded over time, become a high resistance point, and that causes them to melt or the connectors weren't rated ampacity-wise to handle years of extended period charging cycles. I've replaced several where the connections had been cleaned well, yet they still melt down.

Regardless, when it happens, you lose your charging system and tach will act up.

I've also seen weird things happen with turn signals/charging system due to the epoxy resin cracking up from years of heat/use on the back of the reg/rec. Easy change out to fix, if you know to look there.
Bob

[Phare Est]

I've also seen weird things happen with turn signals/charging system due to the epoxy resin cracking up from years of heat/use on the back of the reg/rec. Easy change out to fix, if you know to look there.
Bob

Thanks for the advice about the REG/REC. I've been trying to get it off the frame to get a look underneath it, but one of the screws is stubborn as heck...

[BA80]

Thanks for the advice about the REG/REC. I've been trying to get it off the frame to get a look underneath it, but one of the screws is stubborn as heck...

That's why every time you get a chance replace those stupid Phillips screws with actual BOLTS, do it.

[motoman]

That's why every time you get a chance replace those stupid Phillips screws with actual BOLTS, do it.

...Or, at the least, replace them(JIS) with ACTUAL Phillips metric bolts. JIS stands for Japenese Industrial Steel. For the JIS screws that are everywhere on these Jap bikes, at least get a #2 JIS screwdriver. NAPA, etc. carries them in stock.

[BA80]

Toss those Phillips screws. A regular hex head bolt or an allen head in some spots where it's tight. I've gotten rid of pretty much all the Phillips screws on mine.

That thread really isn't anything special.

[Phare Est]

Toss those Phillips screws. A regular hex head bolt or an allen head in some spots where it's tight. I've gotten rid of pretty much all the Phillips screws on mine.

That thread really isn't anything special.

I will most certainly replace that Phillips screw with a bolt, if I can crack it loose...

Any advice on how to loosen a screw without using a torch ? I've already tried an impact screwdriver and locking pliers, but to no avail.

[BA80]

I've usually had good luck using a good small center punch or chisel. Get a good dimple started on the outer edge then angle the blow force to loosen.

Also, if you have one screw out already try turning the screw and the regulator together to loosen. Sometimes that's just enough to bust it loose

[TruthHammer]

I will most certainly replace that Phillips screw with a bolt, if I can crack it loose...

Any advice on how to loosen a screw without using a torch ? I've already tried an impact screwdriver and locking pliers, but to no avail.

Get a set of easy-outs. They're not really expensive, and they have saved me a lot of headaches.

[3Phase]

Externally Grounded

Thanks for the advice about the REG/REC. I've been trying to get it off the frame to get a look underneath it, but one of the screws is stubborn as heck...

Phare Est, there's nothing to see or do under the regulator/rectifier anyway except make sure the Black ground wires from the harness have good contact with the frame. After you get the screws out you can mount it however you like.

The regulator/rectifier itself is not internally grounded with its aluminum housing, it's externally grounded using the Black wire in its harness connector. It can hang in space or be mounted to a piece of fiberglass, plastic, or wood like an outboard engine shroud or boat hull and it'll work just fine as long as its Black wire in the harness has a good ground.

[DiverRay]

If it's just one screw, drill the head off of it and use pliers to turn whats left once you have the reg/rec off.

[motoman]

If it's just one screw, drill the head off of it and use pliers to turn whats left once you have the reg/rec off.

.....or suggest if you have a Dremal tool, use one of the small cut-off wheels and cut the head off screw, leaving rest to unscrew out, snapping a pair of vice-grips on it.