'73 Merc 1150 RPM Gauge

[GA Paramedic]

I am installing a rpm gauge on my boat. I am not getting any signal from the stator. I checked my connections and nothing. I hooked a test light up and nothing. I tried the old "alternator test" from my experience in cars and the engine will die if the battery is disconnected while running. Any ideas?

 

[daveswaves]

Re: '73 Merc 1150 RPM Gauge

I am installing a rpm gauge on my boat. I am not getting any signal from the stator. I checked my connections and nothing. I hooked a test light up and nothing. I tried the old "alternator test" from my experience in cars and the engine will die if the battery is disconnected while running. Any ideas?

connect the tach wire to one of the yellow wires on your rectifier. The stator on this engine only charges the battery. The engine requires battery to run. Stator wires are notorious for rotting off or at least the insulation. Could be shorted.

 

[monk-monk]

Re: '73 Merc 1150 RPM Gauge

the positive battery cable should never be disconnected while the engine is running because it will damage the rectifier...

 

[GA Paramedic]

Re: '73 Merc 1150 RPM Gauge

connect the tach wire to one of the yellow wires on your rectifier. The stator on this engine only charges the battery. The engine requires battery to run. Stator wires are notorious for rotting off or at least the insulation. Could be shorted.

No good. There isn't a signal coming from the rectifier. I tried the wire from the gauge and a test light. nothing.

 

[daveswaves]

Re: '73 Merc 1150 RPM Gauge

No good. There isn't a signal coming from the rectifier. I tried the wire from the gauge and a test light. nothing.

The tach signal may not be strong enough to light your test light or your rectifier is burned out, or your stator is open. You can check the resistance of the stator with a simple ohmeter, disconnect the two yellow wires from the terminal strip on the side of the intake port covers. If you have an open circuit thats your problem. The rectifier can be tested with the same ohmmeter.

 

[GA Paramedic]

Re: '73 Merc 1150 RPM Gauge

The tach signal may not be strong enough to light your test light or your rectifier is burned out, or your stator is open. You can check the resistance of the stator with a simple ohmeter, disconnect the two yellow wires from the terminal strip on the side of the intake port covers. If you have an open circuit thats your problem. The rectifier can be tested with the same ohmmeter.

The two wires coming from the Stator reveals a closed circuit on the ohm meter. The recitfier, however, releals open circuits betwen all three poles.

Remember from above, I tried the gauge directly on both stator leads; same result.

 

[daveswaves]

Re: '73 Merc 1150 RPM Gauge

The two wires coming from the Stator reveals a closed circuit on the ohm meter. The recitfier, however, releals open circuits betwen all three poles.

Remember from above, I tried the gauge directly on both stator leads; same result.

Your rectifier is gone, remember, the stator puts out an AC signal that has both negative and positive swings. Your gauge is damped, so it only responds to the difference between the swings, ie, zero. When you connect it to one side of the input of the of the rectifier you are getting positive pulses as the negative ones are shunted to ground by the rectifier. Net result is a reading on your meter. You can replace the rectifier with a half wave bridge from Radio Shack.

 

[Faztbullet]

Re: '73 Merc 1150 RPM Gauge

Please dont disconnect battery cables while running as this can destroy trigger and/or switchbox and they aint cheap!!

 

[daveswaves]

Re: '73 Merc 1150 RPM Gauge

Please dont disconnect battery cables while running as this can destroy trigger and/or switchbox and they aint cheap!!

 

[GA Paramedic]

Re: '73 Merc 1150 RPM Gauge

You can replace the rectifier with a half wave bridge from Radio Shack.

I am going to need a little bit more information on this part. Just for giggles, I checked the price of a replacement recitfier at the local boat repair shop. $89.68 The gentleman at the local Radio Shack had no idea what I was talking about when I mentioned "half wave bridge". Looking on the RS webpage, I have found "Full-Wave Bridge"s ranging from 1.4 amps to 25 amps and up to 400V. $1.59 - $3.29 seems to be the going rate for these items as well.

Has anyone taken this option before?

 

[daveswaves]

Re: '73 Merc 1150 RPM Gauge

I am going to need a little bit more information on this part. Just for giggles, I checked the price of a replacement recitfier at the local boat repair shop. $89.68 The gentleman at the local Radio Shack had no idea what I was talking about when I mentioned "half wave bridge". Looking on the RS webpage, I have found "Full-Wave Bridge"s ranging from 1.4 amps to 25 amps and up to 400V. $1.59 - $3.29 seems to be the going rate for these items as well.

Has anyone taken this option before?

http://www.radioshack.com/product/i...roductId=2062584&support=support&tab=features

Heres the link to the radio shack rectifier. You will ground the negative of the rectifier to the ground of the outboard, the positive goes to your battery and the two AC terminals go to the two yellow wires from the stator. Bolt the rectifier to the aluminum front panel so that it can act as a heat sinc.

 

[GA Paramedic]

Re: '73 Merc 1150 RPM Gauge

Heres the link to the radio shack rectifier. You will ground the negative of the rectifier to the ground of the outboard, the positive goes to your battery and the two AC terminals go to the two yellow wires from the stator. Bolt the rectifier to the aluminum front panel so that it can act as a heat sinc.

I have above item in hand. Your directions make complete sense.

Where do I attach the rpm gauge sending wire?

I'll be installing the recitifer tomorrow.

 

[daveswaves]

Re: '73 Merc 1150 RPM Gauge

I have above item in hand. Your directions make complete sense.

Where do I attach the rpm gauge sending wire?

I'll be installing the recitifer tomorrow.

The tach wire will connect to one of the AC connections, either one will do.

 

[GA Paramedic]

Re: '73 Merc 1150 RPM Gauge

The tach wire will connect to one of the AC connections, either one will do.

No good... Hooked up as instructed and still no tach.

First, I checked my connections and found that there is no continuity between the ground wire and any given ground on the block or battery.
(Don't know if this is significant.)

The pos was good and the stator leads were intact as well.

WTH?

 

[Chris1956]

Re: '73 Merc 1150 RPM Gauge

Normal Outboard tachs require signal from the stator, +12VDC ad ground, to operate. If you do not have a ground on the tach, it will not operate properly.

Normally MerControls of your motor's vintage have the three prong moulded connection, especially designed to operate the tach and power other gauges.

 

[GA Paramedic]

Re: '73 Merc 1150 RPM Gauge

Normal Outboard tachs require signal from the stator, +12VDC ad ground, to operate. If you do not have a ground on the tach, it will not operate properly.

Normally MerControls of your motor's vintage have the three prong moulded connection, especially designed to operate the tach and power other gauges.

The tach at the dash has a good pos & ground. The ground that I was checking was going directly to the rectifier.

 

[Chris1956]

Re: '73 Merc 1150 RPM Gauge

The rectifier -DC pole is conected to the cowling or cowling support, to ground it. On the 3 pole Merc Rectifiers, this grounding was the result of bolting the rectifier in place. On the replacement 4 pole rectifiers, you must add a ground wire.

if you operated the motor without the rectifier being grounded, it may have become damaged.

 

[daveswaves]

Re: '73 Merc 1150 RPM Gauge

No good... Hooked up as instructed and still no tach.

First, I checked my connections and found that there is no continuity between the ground wire and any given ground on the block or battery.
(Don't know if this is significant.)

The pos was good and the stator leads were intact as well.

WTH?

Not quite, you forgot to connect the negative of the rectifier to ground. good thing its the cheap radio shack ones

 

[GA Paramedic]

Re: '73 Merc 1150 RPM Gauge

Not quite, you forgot to connect the negative of the rectifier to ground. good thing its the cheap radio shack ones

Then where does the other wire connect to that went to the old rectifier? i think it was brown coming from the wiring harness. There were 4 origionally; two from the stator, pos and the mystery one. Now I have the two from the stator (ac & ac), pos (+), the ground from the cowl (-), ... and the mystery one.

 

[Chris1956]

Re: '73 Merc 1150 RPM Gauge

The brown wire is the tach signal wire. Connect it to either of the yellow AC stator wires.