relay question

[rogertj]

I'm doing the harness for my 85 Vanagon, 1995 Jetta is going in there, I want to plug in the ECU with the battery just to know if it's reading correctly all the codes, in other words, want to know if the ECU is ok because I bought it in wrecking yard, 2 persons already told me to go ahead (protecting all wires from a short that is)

My question is if 30 plug is B+ supply from the battery in to relay what do I connect to 86 plug on the relay if it's a switched positive? Should I plug another battery positive just to do the test?

here's a drawing and it seems that it does go from the battery but with a fuse and then a switch to 86

https://www.hagerty.com/media/maintenance-and-tech/understanding-relays-part-2/

I know that my thread is very self-explanatory but just want to make sure.

And the other question is if I don't have the 3 pin relay for the power supply can it be done with a 4 pin relay for testing purposes?

Thanks all!
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Roger
Had a Carbureted ABA after engoing the heck out of it now going for ABA 2.0 Jetta EFI ill put a garrett in to the tin can later or maybe go electric?
https://www.thesamba.com/vw/forum/viewtopic.php?t=...mp;start=0

[MarkWard]

A standard 4 prong relay has a terminal 30 or bat + its a constant hot. 87 would be your consumer, bulb, motor, ecu etc.

The remaining terminals 85 and 86 are the "holding coil" of the relay. For consistency, the 85 terminal would be a ground and the 86 terminal would be on power. You can switch either the ground or the on power circuit. Also with a simple relay it does not matter if you ground 85 or 86 or power 85 or 86. More sophisticated relays it may matter. Most relays have a diagram of what I just described. I have no idea if I answered your question either.
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[Vanagon Nut]

Hi Roger.

edit: this is for Motronic 2.9 OBD1.

If you open up the ECU and don't see any obvious heat damage, it's probably ok. My original OBD1 ECU had heat damage in at least two places, it still worked.

I've never done this but.....

You don't need relays to bench test the ECU. To reduce potential fault points I'd connect ECU like this. Please double check my work with this page:

http://a2resource.com/electrical/management/motronicvr6aba.html

- switched positive to ECU 38
- positive to ECU 23 and 54
- negative to ECU 1, 7, 55 and 56
- ECU 5 to 12 volt incandescent MIL light bulb (NOT LED)
- positive to that MIL light bulb

I'm nearly 100% certain that ECU supplies negative to turn on the MIL.

Once the ECU is energized, the MIL should light up.

If you wire up the K and L data line connections and use a jumper wire (switch) to activate the DTC blink codes at minimum, you should see 2111: 'RPM sensor' code. 2111 is always displayed when ignition is on but engine is off. I really really doubt you'd see this code but if you get 1111, four blinks, this indicates a fault in ECU.

I wonder if a 9 volt battery would suffice as power supply for testing ECU on the bench?

You can use a 4 pin relay in place of the VW 3 pin power supply relay. This is what I've done on both my OBD1 ABA conversion. Connect B+ to 30, 87 to ECU and main positive junction in harness. Connect positive from ignition switch to 86 and 85 to ECU 9

The power supply relay is switched on negative side. ECU "supplies" (sends) negative to power supply relay once the ECU is turned on via positive from ignition switch.

VW wired that 3 pin relay so that positive flowed inside relay from 30 to 85. Once the ignition is turned on, the ECU sends a ground to 86 of power supply relay which causes the switch in relay to close so it can carry positive to the ECU and main positive junction in wiring harness. (blue/red wires).

I realize my 85/86 wiring scheme to adapt a 4 pin relay for power supply relay is reverse of what the wiring diagram shows but IIRC, VW normally connects ground to relay 85 and positive to 86. I've opened up several Bosch "VW" and generic relays. In each, there is a resistor across 85/86. That part is not voltage polarity sensitive AFAIK.

[rogertj]

Thanks guys Ill check that out and come back to you for the results.

I apreciatte the support!

Roger
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Roger
Had a Carbureted ABA after engoing the heck out of it now going for ABA 2.0 Jetta EFI ill put a garrett in to the tin can later or maybe go electric?
https://www.thesamba.com/vw/forum/viewtopic.php?t=...mp;start=0

[rogertj]

The power supply relay connected and the OBD2 port scanner (cheapo) turned on! (somehow My Engine is OBD1)

Will down load cheapo program to see what happens this big kids game im starting to like it!
_________________
Roger
Had a Carbureted ABA after engoing the heck out of it now going for ABA 2.0 Jetta EFI ill put a garrett in to the tin can later or maybe go electric?
https://www.thesamba.com/vw/forum/viewtopic.php?t=...mp;start=0