Msd wiring diagram

So, i have this old blue gm nascar msd box. 

I don't know the part number because i peeled the sticker off when it was in my duster 15 years ago.

Id like to use it on my 1995 tbi powered Silverado. 

What wiring diagram/how do i do it? Im not sure what to even look up....

EVERY MSD WIRING DIAGRAM KNOWN TO MAN

You'd still have to find out which model you have, but not really because a lot of them just do the exact same thing and just have different connectors attached to make them 'bolt on' for different models. 

So basically you have constant power and ground for the unit,switched ignition power for the unit to turn on, two wires that are the input from your distributor pickup coil or one wire from your factory coil negative wire (one or the other, don't use both), and then power and ground wires out to your coil. 

So basically it triggers off your stock ignition either by directly hooking up to your pickup coil, or hooking up to your factory coil negative wire which is either a. the pickup coil  signal after it's gone through a factory ignition module/ecm which  applied some changes to that raw signal based on conditions, or b. the wire that your points are hooking to ground, if you have points. 

Then it gives new power and ground (higher voltage power wire, faster&multiple switching ground wire) to the coil. 

On a tbi v8 the distributor sends the 'raw signal' to the computer which changes the timing of it and sends it back to the module which then makes the coil spark at that adjusted timing. Signal goes pickup > module > ecm > back to module > coil. So you're better off using the factory coil negative wire as the input to your MSD, because if you picked up the 'raw signal' from the pickup coil or the ignition module before it goes to the ECM, you'd only have base timing and it would never adjust. On an older distributor you COULD hook up directly to the pickup  because all the timing changes would be done by the internal vac/mechanical advance mechanisms.

So, question is: the 5 and 6 series boxes have different diagrams. Which do i use? 6 series, right? 

It looks like the only wiring difference between the basic 5 and 6 series is that 6 has dedicated power/ground and an ign wire to turn it on, whereas the 5 just uses switched power from factory coil positive for both its power and signal to turn on. It also looks like the easiest way to tell a 5 from a 6  without labels is that the 6 will have a spade terminal in the side of the case for a tach output, and the 5 wont.  

So it depends what the other side of your box looks like. Based on the size of your power leads im guessing it's a 6 box, but kinda need to see the other side to know for sure. 

I see what you're saying! 

This is probably a 6 based box, however it does NOT have a tach output. Thats the reason it was changed during the megasquirt experience. 

+eleventy

The only thing I can add is that MSD units do not really like low voltage, and the unit will draw a momentary 30+ amps on the fat red wire and ground when it is recharging the capacitor, so they recommend connecting directly to the battery.  It's critical enough that they prefer you not alter the as-supplied leads to lengthen or shorten.  Looks like that particular item is non optional for you.

Pete, you bring up a good question: ive always mounted the box in the interior somewhere. I see everyone else putting them underhood,  generally on the firewall.

In the engine bay of my truck,  where would be optimal?

Dusterbd13-michael (Forum Supporter) said:

In the engine bay of my truck,  where would be optimal?

In a cool a location as you can find where it won't have rain or snow running on it if you open the hood in adverse conditions.  That's typically on an inner fender.

In reply to APEowner :

Awesome. Thanks!

I want to make this easy to revert back to stock if the box dies out on the road somewhere. 

Msd hardness is 50 bucks. I have everything but a female socket that mimics the dual plug coil terminals. 

Anyone have a source? Msd has them as part of the harness. therefore SOMEONE makes it....

Dusterbd13-michael (Forum Supporter) said:

Msd hardness is 50 bucks. I have everything but a female socket that mimics the dual plug coil terminals. 

Anyone have a source? Msd has them as part of the harness. therefore SOMEONE makes it....

Can you post a picture?  I may be able to ID the manufacturer or I might have something kicking around.

In reply to APEowner :

Best i can do at the moment 

ill try to get a picture of the other side of the connection. This is the coil side, that i would need to replicate with a connector 

Grab one from a junkyard, should be easy to find on an old tbi car or truck. i may have a spare coil harness laying around.  It's a weird thing with interlocking connectors.  I'll post a picture when I find my spare. 

Here's a picture of one of the plugs, they clip to each other and plug into the coil

The part im looking for actually replicates the coil side to plug into the gm harness. The male pin portion that is on millions of tbi and tpi chevy products. I can find them, 9.99 shipped for the pair. But the msd plug in harness has a connector that i haven't found.

In reply to Dusterbd13-michael (Forum Supporter) :

I missed that part, gotcha. Cut the top off a bad coil or maybe a call to MSD customer support?

Dusterbd13-michael (Forum Supporter) said:

In reply to APEowner :

Best i can do at the moment 

ill try to get a picture of the other side of the connection. This is the coil side, that i would need to replicate with a connector 

Sorry.  I don't have anything kicking around that'll work for that.  Accel used to make an adaptor harness that had that connector on it https://www.summitracing.com/parts/acc-140022 but it appears to be no longer available.  The connector on the adaptor appears to be an overmolded part rather than a modular connector so I'm not optimistic about finding one. 

I'm not sure I'm following what you're doing.  Can you change the male connector to something more readily available?

If you give up on having a connector body, it looks like the narrow female spade terminals would work for just sliding on to the male terminals you have. I don't think you're going to find that exact style of connector easily because i dont think it appears anywhere else on a GM aside from that style of coil. 

You might consider adding a more common/generic connector upstream of that in the factory wiring for this theoretical roadside switching back to stock, instead of trying to find a duplicate of that style of connector. 

I hadn't thought of that. Make an msd harness that plugs in to say a four pin weatherpack, and the same with the stock setup. Stuff stock version in glove compartment and pray i never need it!