newguy Posted October 29, 2009 Report Share Posted October 29, 2009 Ok I have a 78 datsun 620 (another one) and it did not come with a OEM tach. I have found one at a junk yard and want to wire it up but the truck currently has a MSD 6AL box and a blaster 2 coil. I'm worried it might fry the tach. I ask napa and they suggest a MSD Tach Adapter. Does anyone have the same setup (MSD) and running an OEM tach? And If so is the signal wire on the tach ran to the negitive post on the msd coil? Quote Link to comment
datzenmike Posted October 29, 2009 Report Share Posted October 29, 2009 Tach signal wire to the neg side of coil should do it. Don't worry it won't blow up all it will 'see' is some 12 volts with sudden drops to zero when the coil is fired. Quote Link to comment
hang_510 Posted October 29, 2009 Report Share Posted October 29, 2009 inductive pick up tachs require adapter #8920 to function w/the MSD box. Quote Link to comment
newguy Posted October 30, 2009 Author Report Share Posted October 30, 2009 Wait I'm confused, mike says one thing and ol,school says another. :confused: is anyone currently running there truck this way? Quote Link to comment
newguy Posted November 1, 2009 Author Report Share Posted November 1, 2009 bump Quote Link to comment
1Low620 Posted November 1, 2009 Report Share Posted November 1, 2009 Ok I have a 78 datsun 620 (another one) and it did not come with a OEM tach. I have found one at a junk yard and want to wire it up but the truck currently has a MSD 6AL box and a blaster 2 coil. I'm worried it might fry the tach. I ask napa and they suggest a MSD Tach Adapter. Does anyone have the same setup (MSD) and running an OEM tach? And If so is the signal wire on the tach ran to the negitive post on the msd coil? Napa? that's like asking a whopper flopper from Burger King about rocket science. Stay away from napa! :D Quote Link to comment
freaky510 Posted November 1, 2009 Report Share Posted November 1, 2009 your best answer I would say is to call Tech Line 915-855-7123 Iam running a cheap aftermarket tach out of my box,it holds up fine and it does jump on power up like mike said :) Quote Link to comment
newguy Posted November 2, 2009 Author Report Share Posted November 2, 2009 Ok I'm going to do it, tomorrow I'm going to wire the OEM tach signal wire directly to the neg. on the coil. This will conferm this question for others.:blink: Quote Link to comment
hang_510 Posted November 2, 2009 Report Share Posted November 2, 2009 is anyone currently running there truck this way? not in a truck, but i have BOTH in use in the sedan. Quote Link to comment
datsun4dsc Posted November 2, 2009 Report Share Posted November 2, 2009 Is there a big gain using MSD box if you already upgraded to EI? Quote Link to comment
hang_510 Posted November 2, 2009 Report Share Posted November 2, 2009 is there a big gain using msd box if you already upgraded to ei? none! Quote Link to comment
Z-train Posted November 2, 2009 Report Share Posted November 2, 2009 Is there a big gain using MSD box if you already upgraded to EI? No power gain IF all things are "correct".BUT,you will see easier starts,cleaner idle and the rev limiter is cheap insurance. Now to the tach-if a 6Al box is in use you MUST wire the tach to the box.And then a "tach adapter" most likely will be needed. Quote Link to comment
datsunaholic Posted November 2, 2009 Report Share Posted November 2, 2009 The tach adaptor is only needed if using an inductive tach- the '73-75 620 tachs are inductive (they are wired in series with the wire running from the points to the coil). The '76-79 620 tachs are wired parallel to the coil, and would just be hooked up to the tach output terminal of the MSD box. With a MSD 6a box, you cannot use the coil neg wire, because the MSD box fires it multiple times instead os a single spark. The tach would jump around, read high, and be inconsistant. Quote Link to comment
hang_510 Posted November 2, 2009 Report Share Posted November 2, 2009 the rev limiter is cheap insurance. OK, i left that out :mellow: Quote Link to comment
newguy Posted November 3, 2009 Author Report Share Posted November 3, 2009 I didn't know there was two types of tachs that came in these trucks. Is there a way to ID what type of tach i found at the junk yard without going back to the yard to see the year of the truck? I have tried wiring it to the tach output on the MSD 6AL box and nothing. The tach adaptor is only needed if using an inductive tach- the '73-75 620 tachs are inductive (they are wired in series with the wire running from the points to the coil). The '76-79 620 tachs are wired parallel to the coil, and would just be hooked up to the tach output terminal of the MSD box. With a MSD 6a box, you cannot use the coil neg wire, because the MSD box fires it multiple times instead os a single spark. The tach would jump around, read high, and be inconsistant. Quote Link to comment
zed Posted November 3, 2009 Report Share Posted November 3, 2009 This may be OT but I have a Magfire coil (40kV) and a Pertronix Ignitor in my L18 - they work very well, but I can't get a tach (rev counter) to work with them. I tried two aftermarket tachs - both jump constantly, read high. I tried splicing in diodes to reduce the voltage - no improvement. Strangely, both these tachs work fine on my other truck - Toyota Landcruiser... Quote Link to comment
RoadRace Posted November 3, 2009 Report Share Posted November 3, 2009 This may be OT but I have a Magfire coil (40kV) and a Pertronix Ignitor in my L18 - they work very well, but I can't get a tach (rev counter) to work with them. I tried two aftermarket tachs - both jump constantly, read high. I tried splicing in diodes to reduce the voltage - no improvement. Strangely, both these tachs work fine on my other truck - Toyota Landcruiser... i have MSD6T, pertronix and Blaster2, autometer tacho works fine. is yours dead or just behaving irratically? if its dead try hooking it up at the coil, just hold it in your hand, try to eliminate wiring. the MSD system becomes more necessary when you have higher cylinder pressures and higher RPM, with stock compression levels and mild cams, power gains will be minimal, if any - especially when you only have 4 cylinders to fire, the stories of big gains are all from big V8's, where they have 4 more cylinders to take care of, doubling the chances of better spark, comparitively speaking. Quote Link to comment
datsunaholic Posted November 3, 2009 Report Share Posted November 3, 2009 This may be OT but I have a Magfire coil (40kV) and a Pertronix Ignitor in my L18 - they work very well, but I can't get a tach (rev counter) to work with them. I tried two aftermarket tachs - both jump constantly, read high. I tried splicing in diodes to reduce the voltage - no improvement. Strangely, both these tachs work fine on my other truck - Toyota Landcruiser... Diodes don't reduce voltage, they block current in one direction. Resistors reduce voltage (actually reduce current, but that has the effect of reducing voltage across the load when placed in series) but that won't do anything with a tach since they record pulses, not voltage. If the tach is proven functional but is still jumping around, you're getting stray signals. Those could be fixed with a condenser, but it could have a detrimental effect on the ignition system. Or it could help if the stray signals are causing other issues. Quote Link to comment
hang_510 Posted November 3, 2009 Report Share Posted November 3, 2009 If the tach is proven functional but is still jumping around, you're getting stray signals. all MSD says is to check that all components are in good working order... :fu: mine jumps ~4000rpm, about where the spark goes from multi- to single- ... no :cursing: idea why either! Quote Link to comment
hughdogz Posted November 4, 2009 Report Share Posted November 4, 2009 There are basically three different tach adapters from MSD. The correct one will depend on if your tach is current controlled, or voltage controlled. They have a tach adapter for each, and the expensive one can run either way. Both (8920): 8910 for current controlled tachs 8910EIS for voltage controlled tachs I'm pretty sure you want to go with the 8910. It is ~half the price of the 8920. Quote Link to comment
hang_510 Posted November 4, 2009 Report Share Posted November 4, 2009 The correct one will depend on if your tach is current controlled, or voltage controlled. I'm pretty sure you want to go with the 8910. It is ~half the price of the 8920. 510 stock tach requires the 8920 (cuz it costs more :rolleyes: :mad:) Quote Link to comment
newguy Posted November 5, 2009 Author Report Share Posted November 5, 2009 There are basically three different tach adapters from MSD. The correct one will depend on if your tach is current controlled, or voltage controlled. They have a tach adapter for each, and the expensive one can run either way. Both (8920): 8910 for current controlled tachs 8910EIS for voltage controlled tachs I'm pretty sure you want to go with the 8910. It is ~half the price of the 8920. This info is very help full. I don't have points in my dizy so can anyone tell me which one of these adpater I'll need? Quote Link to comment
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