Will a 1978 dash and engine bay wire harness work in a 74 620

[hosestop@msn.com]

We are trying to make a guys truck as original as we can ,getting rid of cut harnesses ect. It already has a internal reg. alternator ,but will dash plug in the same as 1974 and 1978 other than that I think do-able.

[mike]

If you use the 78 dash wiring and the 78 engine bay wiring harness... yes, it will work and if done right would actually be an upgrade. Make sure to use the later fuse block from the 78 though as they are different. Also, check the chassis harness for the taillights and stuff... I think they are the same but its been a while. 74 is an oddball year for electrical.

 

Before you install the harness, soak every connection in vinegar and when you install it make damn sure that you've got everything grounded well and have a good fusible link from the battery.  

 

If you are doing the 74 dash harness with the 78 engine harness, I have no idea and wouldn't even try... but that doesn't necessarily mean that you shouldn't ;)  If you look in the FAQ under general discussion here on Ratsun you will find wiring diagrams and FSMs for most 620s so that you can see what differences there were between the years. 

 

As far as dash clusters/guages and heater controls, they are interchangeable with any year 620.

[ggzilla]

1978 harness wont plug into 1972-1974 accessories. You'll have to replace a lot of stuff.

[hosestop@msn.com]

Really ! I will get back to you later today and verify , I expect to replace a few plugs maybe but will try and push out connectors and not splice wires. Thanks for input ,was hoping someone has done it already !

[ggzilla]

Also change the dimmer switch and headlight switch to match the harness.

[datsunaholic]

Almost every plug is different between a '74 and a '78.   74 used rectangular plugs with flat blade connectors.  '78 the plugs vary in design but mostly use round connectors. There are a few exceptions.

 

It can be done, but essentially you'd need an entire '78 donor truck because you would need to replace just about everything electrical, including every single switch (headlight, turn signals, wipers, etc).  The headlight circuit is completely different.  The relays are all different.  The relays are in different places.  The '78 was wired for a remote ignitor EI ignition, not points.  It's not just a matter of the connectors being different, the wires are different and do different things due to the added complexity of some of the systems.   In fact I think the only things in the cab that will "plug in" without changing connectors are the dash cluster itself, the cigarette lighter, and the ignition switch.  Under the hood, a few single-wire things would plug in (temp sender, starter, oil pressure sensor), but the relay set is totally different.

 

'73 harnesses are "close" to a 74 but aren't exactly the same and have the same shortcomings.  '75 was a transition year and the harness is pretty unique.  '76-77 are close enough to each other.  '78-79 are similar but have changes in the ignition system and other small changes.