Jag electronics

[nosox]

Hi guys my name is Les and I drive a 88 Jag XJ-S with a 5.3 V12.I have an issue and looking for help if possible.
Some time ago (after having engine washed :dunno: )my tachometer quit working. The tach is fed from an ignition amplifier which contains a GM ignition module.The module sends info to ECU and tach via 2 resistors,6.8k to ecu and 10k to the tach.I've determined the 10k resistor is shot.I tapped into the feed line and added a new and functional 10k resistor.
The problem????..... the tach works when revs come up but it is reading about 400 rpm slow through all rev ranges.Can I recalibrate the tach? or should I use a different resistor
I've attached a pic of insides of the amplifier
Thanks in advance
Les

[410440]

Most common resistors are +/- 10%.

If you are using a cheap ass radioshack resistor, maybe try ordering a very high quality one.

The higher quality ones (correct me if im wrong) are +/- 1%.

[nosox]

The resistance across new resistor is 9.8k.Its my thinking that less resistance would give higher tach readings based on the fact that when tach is connected directly to the coil then reading is correct at idle but way high when revs get up.
Les