View Full Version : 1979 S&S - guage/electrical question

10-03-2011, 11:16 AM
So I replaced the alternator but guage shows that it's barely charging; like 12.5v - I bought it at Advanced Auto...looked exactly like what was on there when I got boat...any ideas for why it's not charging more?

If the temp/oil press guages are pinned to max until the wire is disconnected from the sender does that mean that there is a short somewhere? Is the short probably behind the dash? Does a bad sender cause the guage to max out?


10-03-2011, 01:39 PM
Is that at idle, it should increase with throttle?

10-03-2011, 03:57 PM
That is @ idle, the guage(s) are maxed out (when connected) so no room for them to increase

10-05-2011, 11:58 AM
Should of been more clear in last posting. I am not 100% sure about the gauges, The gauges are definitley not the problem I think your right about a short some where because they are both doing the same thing. As far as alternator goes if your still wondering whats going on, 12.5 volts is good at idle and it should increase its out put with throttle which you can check in the driveway it will be evident. Sorry I wasnt more help with gauges, but I will do some research and get back with ya.


10-05-2011, 05:43 PM
Jay - that was helpful and thank you, I think the PO put thread tape on the senders which may have something to do with it...we'll see

10-05-2011, 05:57 PM
The way your gauges are set up, when you remove the wire from the sender and leave it disconnected, you should get a zero reading on your gauge. If you then ground that wire, you should get a full reading. If your gauges are pinned until you remove the wire from the sender, you have a wire hooked to ground somewhere that shouldn't be.

As far as charging, I have to have to initially hit above 1500 rpm's to get the alternator fired up and charging at 13.7 volts. 12.4 or so is fine at idle.

Did you have this gauge problem before you changed alternators?

Have yo removed any wires from any of the gauges?

I had problems with corrosion on most of the wiring connectors at my gauges and at my fuse block on my '77 when I got it. You may need to remove the drivers seat and spend some time on your back cleaning things up. If you do, be sure to take a bunch of pictures of where things go as it can be confusing if you lose track. There is very little extra wire in my boat which makes everything more difficult.