Fuel Gauge Quit on 750TZ

[81ZUKI75]

I was replacing the dual HF horns and relay (with a broken mounting tab) on my beater (1982 GS750T) last weekend with a WOLO unit I pulled from my E model. Somewhere in all the re-wiring and such I touched something hot to something grounded and popped the bottom fuse in the fuse box. I think "no biggie", pull the battery ,plug in a new fuse and finish the job. Fast forward a few hours...everything is back together and I take a short spin around the block and I notice that the fuel gauge isn't working. I figured I forgot to plug it in when I re-installed the tank as I've done that before .

Uh-oh...when I went to plug the sender in, I find that its already connected. As I scratch my head, I decide to wait until the next day to dig in again. When I cranked up Monday morning for my commute to work I noticed that the fuel gauge wasn't illuminated. A quick check of all the other lights show no problem so I rode off to work.
Now I've stripped the bike again and found a couple of odd things I don't understand :
1. ~ 4.5 V across the gauge connectors at the harness. Why isn't this 12+V? I think understand if I was measuring AFTER the sender why it would be lower but not before.
2. I dug into the gauge pod and found the 1.7 W wedge bulb blown. Surely this won't keep the gauge from working. I'm struggling with the
wiring diagrams, but I don't see that they're really connected.
3. Dealer price on a fuel gauge is like $85...how can I (the electrically challenged) test the gauge?

 

[tom203]

My bike has a seperate 3 wire plug that feeds fuel gauge- the two wires coming from tank unit and an orange wire that supplies 12 volt. Juice travels down thru fuel tanks variable resistance and returns to gauge as somewhat less voltage. Shorting the tank element wires together should cause gauge to read full, but without 12 volts at that orange wire nothing will happen. My gauge light is powered seperately from this connection.

 

[81ZUKI75]

Fuel Gauge

Fuel Gauge

Thanks for the reply...

I haven't been able to get back to it yet, maybe this weekend. You've confirmed my next two steps though...1) check for 12V at the gauge and 2) short the sender leads and check for a full reading.

I did a little research on the bulb. It's a 1.7W, the only one like it on both my bikes. All the rest are 3.4W. Should be fun finding one of these.

This is why I like having two GS's... it seems that one or the other always needs something, so I keep a spare :dancing: