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I purchased a used tach to replace the inop one that came with the car, but am having a problem getting it to work.
The inop tach was wired with two black ground wires connected via a ring connector to one of the tach mounting posts and a yellow wire to the positive spade connector.
That was clearly incorrect.
The wiring diagram shows a white & black wire from the coil to the tach, a green wire from the voltage stabilizer to the tach, and a ground wire.
Looking behind the panel I found a green wire with spade connector and a white & black wire with a bullet connector. Attached the green to the positive spade connector and the B&W to the male bullet connector on back of tach. No luck.
Tested the voltage on the green wire and it is steady at battery voltage. Tested the B&W and the yellow and had continually changing voltages and erratic readings.
1. Can I test a tach by wiring it directly to the coil and ground?
2. Testing with voltmeter, what should I see on the black & white wire from coil?
3. Does a constant voltage on the green from the voltage stabilizer indicate that the voltage stabilizer is bad? If so, where will I find that behind the ’74 MGB dash? Is the voltage stabilizer critical to the operation of the tach?
4. The only yellow wire that I can find on the diagram is for overdrive switch and transmission interlock switch. The overdrive is working fine so I suppose this is the transmission interlock switch, so I assume that I should be looking for an empty spade connector on the overdrive switch – right?
Thanks for the help.
The inop tach was wired with two black ground wires connected via a ring connector to one of the tach mounting posts and a yellow wire to the positive spade connector.
That was clearly incorrect.
The wiring diagram shows a white & black wire from the coil to the tach, a green wire from the voltage stabilizer to the tach, and a ground wire.
Looking behind the panel I found a green wire with spade connector and a white & black wire with a bullet connector. Attached the green to the positive spade connector and the B&W to the male bullet connector on back of tach. No luck.
Tested the voltage on the green wire and it is steady at battery voltage. Tested the B&W and the yellow and had continually changing voltages and erratic readings.
1. Can I test a tach by wiring it directly to the coil and ground?
2. Testing with voltmeter, what should I see on the black & white wire from coil?
3. Does a constant voltage on the green from the voltage stabilizer indicate that the voltage stabilizer is bad? If so, where will I find that behind the ’74 MGB dash? Is the voltage stabilizer critical to the operation of the tach?
4. The only yellow wire that I can find on the diagram is for overdrive switch and transmission interlock switch. The overdrive is working fine so I suppose this is the transmission interlock switch, so I assume that I should be looking for an empty spade connector on the overdrive switch – right?
Thanks for the help.
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