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Message |
pat young
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, October 20, 2005 - 9:29 pm: | |
I have a 68 Gillig bus with an electrical tach. There is no name or ID on the tach, just a little picture of a crankshaft and piston going up and down. The bus is a rear engine pusher, with a DT466.
At the back of the tach, there are thrre wires. One of the wires goes to ground, the other to the fuse box, and the third one goes aaaaalllll the way to the back of the bus, and hooks up to the center post (of three tiny posts) on top of the alternator.
All wiring is intact, but the tach didn't work, so I got one of thos long plugs you insert into the bell housing, and decided to try powering the tach with a different system. So I grounded one of the terminals, and ran the other to the unused wire on the back of the tach. Lo and behold, now it worked (!).... backwards.
Revving the engine caused the tach to go down to zero, not up.
I reversed the leads on the magnetic plug thing in the bell housing, but got the same results. (I wonder if it would work differently if I drove it to the Southern Hemishphere??)
Anybody got any ideas on this Grande Pain in the neck?
Thanks in advance
Pat Young
Gilligs, Gilligs. |
Gary Stadler (Boogiethecat)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, October 20, 2005 - 9:59 pm: | |
Hi Pat,
What you're seeing makes total sense.
The tach you have is probably set up for the frequency that comes out of your alternator. When you hook up one of those magnetic sensors that sees the flywheel, the frequency coming out of it is LOTS higher than the alternator would create, and waaaay out of range of the tach, so it gets totally confused.
The lug on your alternator is an AC output (taken before the rectifier diodes) and is the only place that tach will work, so I guess you need to figure out what's wrong there. It seems that the tach probably works fine or it wouldn't do anything at all with the flywheel sensor, so it's probably the alternator lug or a wire going to it....
Good luck |
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