[John G]

Hello
I need some advice on a tachometer application. I have a 1980 Merc OB 50 hp 4cyl with a 12 pole stator. I have located a person with several brand new old stock genuine Merc tachometers for sale cheap.

Everywhere I know to look, including my local Merc dealer shows the tach is no longer available, therefore I can't confirm that it will work on my motor.

Does anyone know where I might find out if the tach will work for me?
Thank you for your response.

[MikeW]

Hello John, generally any "outboard" tachometer should work for you. If you have the part number of a tach you want to use post it and I will double check it for you.

[John G]

Thanks Mike.

The number is: MERCURY MERCRUISER THUNDERBOLT TACHOMETER, PART# 79-73370A3. If you need the motor serial number I can go to the boat shed for it.
John

[MikeW]

John, a serial number always helps with Mercury and Mercruiser products.

[John G]

The motor serial number is:5534781

[MikeW]

Hello John, the 79-73370A3 may work if it is a 4 pin tachometer. I don't have one to look at. Mercury makes a new replacement part number# 79-825348A 1. You can also use any OB tach from Teleflex. Bottom line any alternator driven type of tachometer will work. You can hard wire it in or purchase the loom from Mercury to connect it to the control box.

[John G]

Mike,
I already have the 4' harness (Merc# 84 86396 A . I have a photo of it's plug and the control box plug combined but am not sure I can make it attach.

I'll try to describe it. The harness plug is about the size of a dime with 4 holes for pins around a sem-icircle and 1 pin hole in the center. The other end has 5 wires.
Two are exposed (solid purple and solid black). Three wires are bent back and taped to the harness (from factory). They are solid gray, brown/w white tracer line and beige w/blue tracer line.

The control box plug has 4 pins around a semicircle with a blank hole in the center.

Could my rig possibly be for a "4 pin tach" as you mentioned and the harness generic to fit both 4 and 5 pin setups?
JG[/img]

[MikeW]

It has been awhile but if I remember correctly the cable is for both 4 and 5 pin applications. I suggest you call Mercury's Hot line. They have all the cross references for old obsolete part numbers. The phone number is 920-929-5040

[John G]

OK. I will surely call. I thank you for all your help and advice--John G