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Old 10-04-2015, 07:46   #1
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Volvo-Penta MD22L Tachometer Question

Dear Cruisers,

I recently replaced my ignition switch on my late model VP MD22L. The newer switch was clearly an upgrade, and required the use of a clip-on diode to permit the fuel solenoid to stay hot when the engine was started. I got all that sorted out fine.

But ever since installing the new switch, the tachometer does not operate properly.

Turn the key to ON, the tach needle sets to zero.
Start the engine, and about 2 seconds the needle just pegs out.

I've checked the regulator/rectifier and it's fine. I even swapped out the regulator with a backup just to see. Bats charge just fine.

The only thing I can figure is that the new ignition switch is causing this.

Any ideas?

Wiring diagram attached.
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LekiM is offline   Reply With Quote
Old 11-04-2015, 07:20   #2
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Re: Volvo-Penta MD22L Tachometer Question

The 22 series engines used a "one and a half pole" electrical system where the system was single pole during starting and stopping, and two pole the rest of the time. The diodes prevented start and glow plug feedback from energizing the stop system at the same time as starting. Over the years of that style instrument panel, the outer construction of the ignition switch changed some, but the electrical construction was the same. So the change of the switch shouldn't have any effect on the tach.

As you know the tach is driven by the W terminal of the alternator, and this un rectified signal is sent to the tach which counts it and turns it into an RPM reading. I suggest you check wiring continuity from the W terminal grey wire on the alternator thru connection #13 in the harness to the W terminal on the tach. This will show up as an AC milivolt signal on a meter. Also make sure the instrument panel has a good ground connection thru pin 16 in the harness and then thru the ground circuit breaker which is on the engine.


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Old 11-04-2015, 13:13   #3
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Re: Volvo-Penta MD22L Tachometer Question

Originally Posted by LekiM View Post
................. But ever since installing the new switch, the tachometer does not operate properly.
Any ideas?
Yes. Put the old switch back and see if the tach works properly. If it does, the new switch or your modified wiring is the problem. If it doesn't, coincidentally it failed while you were replacing the switch or your switch replacement damaged the tach.
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Old 11-04-2015, 15:57   #4
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Re: Volvo-Penta MD22L Tachometer Question

This may not be useful info, but could reveal something regarding the new switch.

I have two MD22L's and replaced the original Volvo 5 position control switches several years ago and did not have any tach problems.

The original switches on my engines were 5 positions, left to right: Stop (fuel shut off), Off, On, Glow, Start. Spring return to On from Start; spring return to Off from Stop.

Not wanting to spend the way-too-high costs for replacement Volvo switches, I procured industrial grade 3 position Cole-Herse switches (Off, On, Start, spring return to On) and two momentary contact Cole-Herse push buttons for the Glow and Stop functions. Analyzing the wiring from old to new was straightforward and everything worked as predicted. Cost was about 1/3 the cost of new Volvo switches. Rum money.

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