Hello friends, first thread for me here, but I've been lurking for a couple months. I purchased an 89 a couple months ago that has been switched from TBI to Carb and was working on cleaning up the underhood wiring. I have seen where some people use the Bussmann RTMR boxes for relays and fuses and wanted to do the same because of it's modularity. Of course right now I just need fan and fuel pump relays (and maybe high speed HVAC fan, but a/c is deleted). There are two of these boxes that I have seen used, one with 2 internal busses and the other with only one buss on the fuse side. I currently have the 2 buss version and am struggling to understand how I can wire up the fan relay since it is negative trigger from the temp sensor, but then the fuel pump is a positive trigger from ignition. Is this possible with the box that I have since one buss is power and the other is ground? I messaged @vorteciroc about it, but I know we all have busy lives and I may have been a bit confused when I tried to convey what I was trying to accomplish. Thanks in advance for any help you guys can provide.

Bussmann / Eaton 15305-2-2-4 Front

Bussmann / Eaton 15305-2-2-4 Rear

 

I think the B+ busbar is used for the high current switched power and not the relay control. You would still wire individual wires for relay field coils to control the relay on/off. The relay coils will not share wiring so you can wire one relay coil with high side switching, and the other relay coil with low side switching.

Each busbar has a max rated continuous current. Make sure the total current of all components together on that busbar do not exceed that rating.

 

Thanks Qwk, but I have seen these boxes sold as pre-wired kits like this: LINK and they always say "relays can be positive or negative triggered, but not a mixture of both." I think that's where my confusion lies. I'm a decent parts-changer (I swear,) but I tend to overthink this wiring stuff.
P.S., your build thread was hours of enjoyment... The highs... the lows, it had it all.

 

My guess is that's just a result of their design choices. They probably spliced all the relay coils to a common wire on one side. Since you're wiring yours from scratch then you can wire up your coils any which way you want.

That's real life right there! I had almost zero experience when I started that thread. I'll be honest, it was difficult for me at times.

 

Wait a minute, I think I steered you wrong. Double busbar will have a common rail to all fuses and a common rail to all relays on terminal 86. All the switching will have to be on the ground side. You can't reverse polarity relays with flyback diode (and I would choose relays with flyback diode).

If you want to wire relay coils all individually then you'll not want a busbar on that side of power center. I think what you want is the style shown in Figure 4 of this document, https://www.waytekwire.com/datasheet/46343.pdf

 

Thanks again @QwkTrip I've got the single buss RTMR on the way and might, just might be able to get this turd back on the road in the next couple weeks.

 

I am just catching up on PMs...
Thanks for Tagging me @RJDin10isee .


I see that QwkTrip has got you squared-away.

You are in good hands!