1971 1150 with reg/rectifier-tach incorrect

N

NJCinMN

Petty Officer 3rd Class
Joined
Jun 4, 2008
Messages
86
Hey all,
Just repowered from a 1969 merc 1000 to a 1971 1150. A 4 wire regulator/rectifier had been added in place of original rectifier. I had a newer quicksilver tach hooked up to merc 1000 by switching "signal" wire to yellow rectifier wire and tach read accurately. Did the same wire switch on the 1971 1150. Motor screams, volt guage shows charging @ 13-14 when wot, but tach only says 4000 rpm. Quite sure tach is incorrect (only running 17p prop and last bit of throttle just over-revs motor. Seems correct @ idle around 800. Would regulator affect this? Is there a different procedure if you have a regulator/rectifier?

Thanks for any ideas.
 
F

Fuzzytbay

Chief Petty Officer
Joined
Jun 6, 2008
Messages
557
Re: 1971 1150 with reg/rectifier-tach incorrect

I don't think the pluse setting on the tach is any different between them, but if it is, then that could explain the difference.
 
C

Chris1956

Supreme Mariner
Joined
Mar 25, 2004
Messages
27,148
Re: 1971 1150 with reg/rectifier-tach incorrect

Without knowing what type of VR is installed, it is hard to answer the Q accurately. A stock Merc VR, does not mess up a tachometer's reading. Are you currently connected to the yellow stator wire? Is there a yellow or grey or grey/yellow VR wire that is not connected? If so, you might try it. A lot of VRs pull the stator signal thru for the tach. The newer color scheme is grey for the signal. Some use grey/yellow.
 
N

NJCinMN

Petty Officer 3rd Class
Joined
Jun 4, 2008
Messages
86
Re: 1971 1150 with reg/rectifier-tach incorrect

I don't think it's a mercury. Looks universal. I'm pretty sure it only has 4 male spade terminals and then wires attached...black(grounded to lower shroud), red(into wiring harness) and two yellow for stator. I'm currently tied into one of the yellow wires before attached to the reg/rec. I'll take another look and verify.
 
N

NJCinMN

Petty Officer 3rd Class
Joined
Jun 4, 2008
Messages
86
Re: 1971 1150 with reg/rectifier-tach incorrect

Not the end of the world. Next time out I'll check rpms with reflective tape on flywheel and handheld laser tach but its always nice to have a functioning tach in the dash.
 
C

Chris1956

Supreme Mariner
Joined
Mar 25, 2004
Messages
27,148
Re: 1971 1150 with reg/rectifier-tach incorrect

That sounds like an aftermarket recitifer, and not a VR. A picture would cinch it.

Disconnect both the yellow wires from the device, and start the motor, If the tach works, it is OK, and the rectifier is likely bad. If the tach doesn't work, check for AC voltage across the two yellow wires. If you have some (use a 500V AC scale) AC voltage, the stator is good, and the tach is bad.
 
N

NJCinMN

Petty Officer 3rd Class
Joined
Jun 4, 2008
Messages
86
Re: 1971 1150 with reg/rectifier-tach incorrect

Will do the tests. Just a thought, if either rectifier or stator were bad then how could I be getting the 14 volts charge with motor runninng?

Also, I think you're right on it being just an aftermarket rectifier. Can you add a voltage regulator to a rectifier?
 
C

Chris1956

Supreme Mariner
Joined
Mar 25, 2004
Messages
27,148
Re: 1971 1150 with reg/rectifier-tach incorrect

The rectifier is four diodes arranged in a bridge configuration. One could be blown, and could cut the charging rate in half, but it will still charge.

Google "Bridge Rectifier" and you can see how the diodes are connected.

Normally a motor will have a VR or a rectifier, but not both. A VR will contain a internal "Diode body", that serves to rectify the voltage. On that motor a VR is not really necessary since the output is < 9Amps. A decent starting battery acts as a load and absorbs the charge current, thus regulating the voltage.
 
N

NJCinMN

Petty Officer 3rd Class
Joined
Jun 4, 2008
Messages
86
Re: 1971 1150 with reg/rectifier-tach incorrect

Googled "Bridge Rectifier". Chris1956, thanks for the in depth info on this tach/regulator/rectifier discussion. It all makes perfect sense now and I love learning about these old Mercs. Hopefully it's the rectifier as a new universal is only about $3.
 
N

NJCinMN

Petty Officer 3rd Class
Joined
Jun 4, 2008
Messages
86
Re: 1971 1150 with reg/rectifier-tach incorrect

Finally got around to this...have voltage across yellow wires. Disconected yellow wires and tach still saying 3500. Put in a new rectifier anyway. Still reading 3500 rpm @ wot. Tach must have went bad. I'm gonna order a new one and see what it reads.
 
You must log in or register to reply here.
Top